Nucleobase editors having reduced off-target deamination and methods of using same to modify a nucleobase target sequence

Abstract

The invention features nucleobase editors and multi-effector nucleobase editors having an improved editing profile with minimal off-target deamination, compositions comprising such editors, and methods of using the same to generate modifications in target nucleobase sequences.

Description

CROSS REFERENCE TO RELATED APPLICATIONS This application is an International PCT Application which claims the benefit of U.S. Provisional Application Nos. 62 / 799,702, filed January 31, 2019; 62 / 835,456, filed April 17, 2019; and 62 / 941,569, filed November 27, 2019, the contents of each of which are incorporated by reference herein in its entirety. BACKGROUND Targeted editing of nucleic acid sequences, for example, the targeted cleavage or the targeted modification of genomic DNA is a highly promising approach for the study of gene function and also has the potential to provide new therapies for human genetic diseases. Currently available base editors include cytidine base editors (e.g., BE4) that convert target C^G base pairs to T*A and adenine base editors (e.g., ABE7.10) that convert A*T to G<‘. There is a need in the art for improved base editors capable of inducing modifications within a target sequence with greater specificity and efficiency. SUMMARY In one particular aspect, the invention encompasses a cytidine base editor fusion protein comprising (i) a polynucleotide programmable DNA binding domain and (ii) a cytidine deaminase comprising an amino acid sequence with at least 90% sequence identity to the amino acid sequence MTSEKGPSTGDPTLRRRIESWEFDVFYDPRELRKETCLLYEIKWGMSRKIWRSSGKNTTNHV EVNFIKKFTSERRFHSSISCSITWFLSWSPCWECSQAIREFLSQHPGVTLVIYVARLFWHMD QRNRQGLRDLVNSGVTIQIMRASEYYHCWRNFVNYPPGDEAHWPQYPPLWMMLYALELHCII LSLPPCLKISRRWQNHLAFFRLHLQNCHYQTIPPHILLATGLIHPSVTWR and further comprising an alteration selected from the group consisting of R33A, K34A, R52A, and H122A, 2020216484   21 Jul 2026 wherein the cytidine base editor fusion protein has an increased ratio of in cis to in trans activity (in cis:in trans) as compared to a standard cytidine base editor fusion protein comprising a rat APOBEC-1 cytidine deaminase (rAPOBEC-1) and a Cas9 nickase. In one other aspect, the invention encompasses a cell comprising the cytidine base editor fusion protein of a preceding aspect, with the proviso that the cell is not a human ovum, a human totipotent cell, a human zygote, or a human embryonic cell. In one other aspect, the invention encompasses a molecular complex comprising the cytidine base editor fusion protein of a preceding aspect and one or more of a guide RNA, a tracrRNA, or a target DNA molecule. In one other aspect, the invention encompasses a method of editing a nucleobase of a DNA molecule, the method comprising contacting the DNA molecule with the cytidine base editor fusion protein of a preceding aspect and converting a first nucleobase of the DNA molecule to a second nucleobase, with the proviso that, if the method is performed in vivo, the contacting is not made in a human ovum, a human totipotent cell, a human zygote, or a human embryo. In one other aspect, the invention encompasses a polynucleotide molecule encoding the cytidine base editor fusion protein of a preceding aspect. In one other aspect, the invention encompasses an expression vector comprising a polynucleotide molecule of a preceding aspect. In one other aspect, the invention encompasses a kit comprising the cytidine base editor fusion protein of a preceding aspect, the molecular complex of a preceding aspect, the polynucleotide of a preceding aspect, or the expression vector of a preceding aspect. In one other aspect, the invention encompasses a method of editing a nucleobase of a DNA molecule, the method comprising contacting a DNA molecule with the cytidine base editor fusion protein of a preceding aspect and converting a first nucleobase of the DNA molecule to a second nucleobase, with the proviso that, if the method is performed in vivo, 2020216484   21 Jul 2026 the contacting is not made in a human ovum, a human totipotent cell, a human zygote, or a human embryo. In one other aspect, the invention encompasses a cytidine deaminase comprising an amino acid sequence that has at least 90% identity to the amino acid sequence MTSEKGPSTGDPTLRRRIESWEFDVFYDPRELRKETCLLYEIKWGMSRKIWRSSGKNTTNHV EVNFIKKFTSERRFHSSISCSITWFLSWSPCWECSQAIREFLSQHPGVTLVIYVARLFWHMD QRNRQGLRDLVNSGVTIQIMRASEYYHCWRNFVNYPPGDEAHWPQYPPLWMMLYALELHCII LSLPPCLKISRRWQNHLAFFRLHLQNCHYQTIPPHILLATGLIHPSVTWR and further comprises an alteration selected from the group consisting of R33A, K34A, R52A, and H122A, wherein a cytidine base editor fusion protein comprising the cytidine deaminase and a polynucleotide programmable DNA binding domain has an increased ratio of in cis to in trans activity (in cis:in trans) as compared to a standard cytidine base editor fusion protein comprising a rat APOBEC-1 cytidine deaminase (rAPOBEC-1) and a Cas9 nickase. General aspects of the present disclosure are also provided herein. These are set out below and in the description that follows. As indicated below, the present disclosure features nucleobase editors and multieffector nucleobase editors having an improved editing profile with minimal off-target deamination, compositions comprising such editors, and methods of using the same to generate modifications in target nucleobase sequences. In one aspect provided herein is a cytidine base editor comprising (i) a polynucleotide programmable DNA binding domain and (ii) a cytidine deaminase, wherein the cytidine base editor has an increased ratio of in cis to in trans activity (in cis:in trans) as compared to a standard cytidine base editor. In some embodiments, the standard cytidine base editor comprises (i) a polynucleotide programmable DNA binding domain and (ii) an APOBEC cytidine deaminase. In some embodiments, the APOBEC cytidine deaminase of the standard cytidine base editor is a rat APOBEC-1 cytidine deaminase (rAPOBEC-1). In some embodiments, the 2020216484   21 Jul 2026 polynucleotide programmable DNA binding domain of the standard cytidine base editor is a Cas9 nickase. In some embodiments, the standard cytidine base editor comprises a uracil glycosylase inhibitor (UGI) domain. In some embodiments, the standard cytidine base editor is a BE3 or BE4. In some embodiments, the increased ratio of in cis to in trans activity is increased by at least 2, 2.5, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60 fold or more. In some embodiments, the cytidine base editor has at least 50%, 60%, 70%, 80%, 90%, 95%, 100%, 105%, 110%,115%, 120%, or more in cis activity as compared to the standard cytidine base editor. In some embodiments, the cytidine base editor has at least 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, or more fold less in trans activity as compared to the standard cytidine base editor. In some embodiments, the cytidine deaminase is selected from the group consisting of APOBEC1, APOBEC2, APOBEC3A, APOBEC3B, APOBEC3C, APOBEC3D, APOBEC3E, APOBEC3F, APOBEC3G, APOBEC3H, APOBEC4, Activation-induced (cytidine) deaminase (AID), hAPOBEC1, rAPOBEC1, ppAPOBEC1, AmAPOBEC1 (BEM3.31), ocAPOBEC1, SsAPOBEC2 (BEM3.39), hAPOBEC3A, maAPOBEC1, mdAPOBEC1, cytidine deaminase 1 (CDA1), hA3A, RrA3F (BEM3.14), PmCDA1, AID (Activation-induced cytidine deaminase; AICDA), hAID, and FENRY. In some embodiments, the cytidine deaminase is APOBEC1. In some embodiments, the cytidine deaminase is (a) an APOBEC-1 from Mesocricetus auratus (MaAPOBEC-1), Pongo pygmaeus (PpAPOBEC-1), Oryctolagus cuniculus (OcAPOBEC-1), Monodelphis domestica (MdAPOBEC-1), or Alligator mississippiensis (AmAPOBEC-1), (b) an APOBEC-2 from Pongo pygmaeus (PpAPOBEC-2), Bos taurus (BtAPOBEC-2), or Sus scrofa (SsAPOBEC-2), (c) an APOBEC-4 from Macaca fascicularis (MfAPOBEC-4), (d) an AID from Canis lupus familaris (ClAID) or Bos Taurus (BtAID), (e) a yeast cytosine deaminase (yCD) from Saccharomyces cerevisiae, (f) an APOBEC-3F from Rhinopithecus roxellana (RrA3F), or (g) a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to any one of (a)-(f). In some embodiments, the cytidine deaminase is an APOBEC-1 from Mesocricetus auratus (MaAPOBEC-1), Pongo pygmaeus (PpAPOBEC-1), Oryctolagus cuniculus 2020216484   21 Jul 2026 (OcAPOBEC-1), Monodelphis domestica (MdAPOBEC-1), or a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. In some embodiments, the cytidine deaminase is rAPOBEC1. In some embodiments, the cytidine deaminase is hAPOBEC3A. In some embodiments, the cytidine deaminase is ppAPOBEC1. In some embodiments, the cytidine deaminase is an APOBEC-2 derived from Pongo pygmaeus (PpAPOBEC-2), Bos taurus (BtAPOBEC-2), or Sus scrofa (SsAPOBEC-2), or a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. In some embodiments, the cytidine deaminase is an APOBEC-4 derived from Macaca fascicularis (MfAPOBEC-4), or a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. In some embodiments, the cytidine deaminase is an AID from Canis lupus familaris (ClAID), Bos Taurus (BtAID), or a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. In some embodiments, the cytidine deaminase is a yeast cytosine deaminase (yCD) from Saccharomyces cerevisiae, or a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. In some embodiments, the cytidine deaminase is an APOBEC-3F from Rhinopithecus roxellana (RrA3F), or a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. In some embodiments, the cytidine deaminase is any one of the cytidine deaminases provided in Table 13, or a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. In some embodiments, the cytidine deaminase is APOBEC-3F from Rhinopithecus roxellana (RrA3F), APOBEC-1 from Alligator mississippiensis (AmAPOBEC-1), APOBEC-2 from Sus scrofa (SsAPOBEC-2), APOBEC-1 from Pongo pygmaeus (PpAPOBEC-1), or a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. In some embodiments, the cytidine deaminase comprises one or more alterations at positions R15X, R16X, H21X, R30X, R33X, K34X, R52X, K60X, R118X, H121X, H122X, R126X, R128X, R169X, R198X, T36X, H53X, V62X, L88X, W90X, Y120X or R132X as 2020216484   21 Jul 2026 numbered in SEQ ID NO: 1 or one or more corresponding alterations thereof, wherein X is any amino acid. In some embodiments, the cytidine deaminase comprises one or more alterations selected from the group consisting of R15A, R16A, H21A, R30A, R33A, K34A, R52A, K60A, R118A, H121A, H122A, H122L, R126A, R128A, R169A, R198A, T36A, H53A, V62A, L88A, W90F, W90A, Y120F, Y120A, H121R, H122R, R126E, W90Y, and R132E as numbered in SEQ ID NO: 1 or one or more corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises a combination of alterations selected from the group consisting of: K34A+R33A, K34A+H122A, K34A+Y120F, K34A+R52A, K34A+H122A, K34A+H121A, W90A+ R126E, W90Y+R126E, H121R+H122R, R126+R132E, W90Y+R132E, and W90Y+R126E+R132E as numbered in SEQ ID NO: 1 or corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises an alteration at position Y120F and one or more alterations selected from the group consisting of R33A, W90F, K34A, R52A, H122A, and H121A as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises an alterations at position Y130X or R28X as numbered in SEQ ID NO: 1 or a corresponding alteration thereof, wherein X is any amino acid. In some embodiments, the cytidine deaminase comprises an alterations at position Y130A or R28A as numbered in SEQ ID NO: 1 or a corresponding alteration thereof. In some embodiments, the cytidine deaminase comprises alterations at positions Y130A and R28A as numbered in SEQ ID NO: 1 or corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises one or more alterations at positions H122X, K34X, R33X, W90X, or R128X as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof, wherein X is any amino acid. In some embodiments, the cytidine deaminase comprises one or more alterations selected from the group consisting of H122A, K34A, R33A, W90F, W90A, and R128A as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises a combination of alterations selected from the group consisting of: R33A+K34A, W90F+K34A, R33A+K34A+W90F, and R33A+K34A+H122A+W90F as numbered in SEQ ID NO: 1 or corresponding alterations thereof. 2020216484   21 Jul 2026 In some embodiments, the cytidine deaminase comprises an amino acid sequence that has at least 80% identity to amino acid sequence: MTSEKGPSTGDPTLRRRIESWEFDVFYDPRELRKETCLLYEIKWGMSRKIWRSSGKNTTNHVEVNFIKKFT SERRFHSSISCSITWFLSWSPCWECSQAIREFLSQHPGVTLVIYVARLFWHMDQRNRQGLRDLVNSGVTIQ IMRASEYYHCWRNFVNYPPGDEAHWPQYPPLWMMLYALELHCIILSLPPCLKISRRWQNHLAFFRLHLQNC HYQTIPPHILLATGLIHPSVTWR. In some embodiments, the cytidine deaminase comprises an amino acid sequence that has at least 80% identity to amino acid sequence: MKPQIRDHRPNPMEAMYPHIFYFHFENLEKAYGRNETWLCFTVEIIKQYLPVPWKKGVFRNQVDPETHCHA EKCFLSWFCNNTLSPKKNYQVTWYTSWSPCPECAGEVAEFLAEHSNVKLTIYTARLYYFWDTDYQEGLRSL SEEGASVEIMDYEDFQYCWENFVYDDGEPFKRWKGLKYNFQSLTRRLREILQ. In some embodiments, the cytidine deaminase comprises an amino acid sequence that has at least 80% identity to amino acid sequence: MADSSEKMRGQYISRDTFEKNYKPIDGTKEAHLLCEIKWGKYGKPWLHWCQNQRMNIHAEDYFMNNIFKAK KHPVHCYVTWYLSWSPCADCASKIVKFLEERPYLKLTIYVAQLYYHTEEENRKGLRLLRSKKVIIRVMDIS DYNYCWKVFVSNQNGNEDYWPLQFDPWVKENYSRLLDIFWESKCRSPNPW. In some embodiments, the cytidine deaminase comprises an amino acid sequence that has at least 80% identity to amino acid sequence: MDPQRLRQWPGPGPASRGGYGQRPRIRNPEEWFHELSPRTFSFHFRNLRFASGRNRSYICCQVEGKNCFFQ GIFQNQVPPDPPCHAELCFLSWFQSWGLSPDEHYYVTWFISWSPCCECAAKVAQFLEENRNVSLSLSAARL YYFWKSESREGLRRLSDLGAQVGIMSFQDFQHCWNNFVHNLGMPFQPWKKLHKNYQRLVTELKQILREEPA TYGSPQAQGKVRIGSTAAGLRHSHSHTRSEAHLRPNHSSRQHRILNPPREARARTCVLVDASWICYR. In some embodiments, the cytidine deaminase comprises a H122A alteration. In some embodiments, the cytidine base editor of any one of aspects above, further comprises at least one adenosine deaminase or catalytically active fragments thereof. In some embodiments, the adenosine deaminase is a TadA deaminase. In some embodiments, the TadA deaminase is a modified adenosine deaminase that does not occur in nature. In some embodiments, the cytidine base editor comprises two adenosine deaminases that are the same or different. In some embodiments, the two adenosine deaminases are capable of forming heterodimers or 2020216484   21 Jul 2026 homodimers. In some embodiments, the adenosine deaminase domains are a wild-type TadA and TadA7.10. In some embodiments, the adenosine deaminase comprises a deletion of the C terminus beginning at a residue selected from the group consisting of 149, 150, 151, 152, 153, 154, 155, 156, and 157. In some embodiments, the adenosine deaminase is missing 1, 2, 3, 4, 5 ,6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 6, 17, 18, 19, or 20 N-terminal amino acid residues relative to a full-length adenosine deaminase. In some embodiments, the adenosine deaminase is missing 1, 2, 3, 4, 5 ,6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 6, 17, 18, 19, or 20 C-terminal amino acid residues relative to a full-length adenosine deaminase. In some embodiments, the at least one nucleobase editor domain further comprises an abasic nucleobase editor. In some embodiments, the cytidine base editor of any one of aspects above, further comprises one or more Nuclear Localization Signals (NLS). In some embodiments, the cytidine base editor comprises an N-terminal NLS and / or a C-terminal NLS. In some embodiments, the NLS is a bipartite NLS. In some embodiments, the polynucleotide programmable DNA binding domain is a Cas9. In some embodiments, the polynucleotide programmable DNA binding domain is a Staphylococcus aureus Cas9 (SaCas9), a Streptococcus pyogenes Cas9 (SpCas9), or variants thereof. In some embodiments, the polynucleotide programmable DNA binding domain comprises a nuclease dead Cas9 (dCas9), a Cas9 nickase (nCas9), or a nuclease active Cas9. In some embodiments, the polynucleotide programmable DNA binding domain comprises a catalytic domain capable of cleaving the reverse complement strand of the nucleic acid sequence. In some embodiments, the polynucleotide programmable DNA binding domain does not comprise a catalytic domain capable of cleaving the nucleic acid sequence. In some embodiments, the Cas9 is a dCas9. In some embodiments, the Cas9 is a Cas9 nickase (nCas9). In some embodiments, the nCas9 comprises amino acid substitution D10A or a corresponding amino acid substitution thereof. In some embodiments, the cytidine base editor of any one of aspects above, further comprises one or more Uracil DNA glycosylase inhibitors (UGI). In some embodiments, the one or more UGI is derived from Bacillus subtilis bacteriophage PBS1 and inhibits human UDG activity. In some embodiments, the cytidine base editor comprises two Uracil DNA 2020216484   21 Jul 2026 glycosylase inhibitors (UGI). In some embodiments, the cytidine base editor of any one of aspects above, further comprises one or more linkers. Provided herein is a cell comprising the cytidine base editor of any one of aspects above. In some embodiments, the cell is a bacterial cell, plant cell, insect cell, or mammalian cell. Provided herein is a molecular complex comprising the cytidine base editor of any one of aspects above and one or more of a guide RNA sequence, a tracrRNA sequence, or a target DNA sequence. Provided herein is a method of editing a nucleobase of a nucleic acid sequence, the method comprising contacting the nucleic acid sequence with the cytidine base editor of any one of aspects above and converting a first nucleobase of the DNA sequence to a second nucleobase. In some embodiments, the method further comprises contacting the nucleic acid sequence with a guide polynucleotide to effect the conversion. In some embodiments, the first nucleobase is cytosine and the second nucleobase is thymidine. In one aspect, provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and at least one nucleobase editor domain comprising a cytidine deaminase, wherein the cytidine deaminase is (i) an APOBEC-1 from Mesocricetus auratus (MaAPOBEC-1), Pongo pygmaeus (PpAPOBEC-1), Oryctolagus cuniculus (OcAPOBEC-1), Monodelphis domestica (MdAPOBEC-1), or Alligator mississippiensis (AmAPOBEC-1), (ii) an APOBEC-2 from Pongo pygmaeus (PpAPOBEC-2), Bos taurus (BtAPOBEC-2), or Sus scrofa (SsAPOBEC-2), (iii) an APOBEC-4 from Macaca fascicularis 2020216484   17 Mar 2026 (MfAPOBEC-4), (iv) an AID from Canis lupus familaris (ClAID) or Bos Taurus (BtAID), (v) a yeast cytosine deaminase (yCD) from Saccharomyces cerevisiae, (vi) an APOBEC-3F from Rhinopithecus roxellana (RrA3F), or (vii) a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to any one 5 of (i)-(viii). In one aspect provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and at least one nucleobase editor domain comprising a cytidine deaminase, wherein the cytidine deaminase is an APOBEC-1 from Mesocricetus auratus (MaAPOBEC-1), Pongo pygmaeus (PpAPOBEC-1), Oryctolagus cuniculus 10 (OcAPOBEC-1), Monodelphis domestica (MdAPOBEC-1), or a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. In one aspect provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and at least one nucleobase editor domain comprising a 15 cytidine deaminase, wherein the cytidine deaminase is an APOBEC-2 from Pongo pygmaeus (PpAPOBEC-2), Bos taurus (BtAPOBEC-2), or Sus scrofa (SsAPOBEC-2), or a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. In one aspect provided herein is a fusion protein comprising a polynucleotide 20 programmable DNA binding domain and at least one nucleobase editor domain comprising a cytidine deaminase, wherein the cytidine deaminase is an APOBEC-4 from Macaca fascicularis (MfAPOBEC-4), or a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. In one aspect provided herein is a fusion protein comprising a polynucleotide 25 programmable DNA binding domain and at least one nucleobase editor domain comprising a cytidine deaminase, wherein the cytidine deaminase is an AID from Canis lupus familaris (ClAID), Bos Taurus (BtAID), or a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto In one aspect provided herein is a fusion protein comprising a polynucleotide 30 programmable DNA binding domain and at least one nucleobase editor domain comprising a cytidine deaminase, wherein the cytidine deaminase is a yeast cytosine deaminase (yCD) from Saccharomyces cerevisiae, or a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. 2020216484   17 Mar 2026 In one aspect provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and at least one nucleobase editor domain comprising a cytidine deaminase, wherein the cytidine deaminase is an APOBEC-3F from Rhinopithecus roxellana (RrA3F), or a cytidine deaminase having an amino acid sequence that is at least 5   80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. In one aspect provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and at least one nucleobase editor domain comprising a cytidine deaminase, wherein the cytidine deaminase is any one of the cytidine deaminases provided in Table 13, or a cytidine deaminase having an amino acid sequence that is at least 10   80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. In one aspect provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and at least one nucleobase editor domain comprising a cytidine deaminase, wherein the cytidine deaminase is APOBEC-3F from Rhinopithecus roxellana (RrA3F), APOBEC-1 from Alligator mississippiensis (AmAPOBEC-1), APOBEC- 15   2 from Sus scrofa (SsAPOBEC-2), APOBEC-1 from Pongo pygmaeus (PpAPOBEC-1), or a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. In some embodiments, the cytidine deaminase comprises one or more alterations at positions R15X, R16X, H21X, R30X, R33X, K34X, R52X, K60X, R118X, H121X, H122X, 20  R126X, R128X, R169X, R198X, T36X, H53X, V62X, L88X, W90X, Y120X or R132X as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof, wherein X is any amino acid. In some embodiments, the cytidine deaminase comprises one or more alterations selected from the group consisting of R15A, R16A, H21A, R30A, R33A, K34A, R52A, K60A, R118A, H121A, H122A, H122L, R126A, R128A, R169A, R198A, T36A, 25  H53A, V62A, L88A, W90F, W90A, Y120F, Y120A, H121R, H122R, R126E, W90Y, and R132E as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises a combination of alterations selected from the group consisting of: K34A+R33A, K34A+H122A, K34A+Y120F, K34A+R52A, K34A+H122A, K34A+H121A, W90A+ R126E, W90Y+R126E, H121R+H122R, 30  R126+R132E, W90Y+R132E, and W90Y+R126E+R132E as numbered in SEQ ID NO: 1 or corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises a combination of alterations selected from the group consisting of Y120F and one or more 2020216484   17 Mar 2026 alterations selected from the group consisting of R33A, W90F, K34A, R52A, H122A, and H121A as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises one or more alterations at positions Y130X or R28X as numbered in SEQ ID NO: 1, or one or more corresponding 5 alterations thereof, wherein X is any amino acid. In some embodiments, the cytidine deaminase comprises one or more alterations selected from the group consisting of Y130A and R28A as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises alterations Y130A and R28A as numbered in SEQ ID NO: 1 or corresponding alterations thereof. In some embodiments, the 10 cytidine deaminase comprises one or more alterations at positions H122X, K34X, R33X, W90X, or R128X as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof, wherein X is any amino acid. In some embodiments, the cytidine deaminase comprises one or more alterations selected from the group consisting of H122A, K34A, R33A, W90F, W90A, and R128A as numbered in SEQ ID NO: 1, or one or more 15 corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises a combination of alterations selected from the group consisting of: R33A+K34A, W90F+K34A, R33A+K34A+W90F, and R33A+K34A+H122A+W90F as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises a 20   H122A alteration as numbered in SEQ ID NO: 1, or a corresponding alteration thereof. In some embodiments, the cytidine deaminase is rAPOBEC1 and comprises one or more alterations selected from the group consisting of R15A, R16A, H21A, R30A, R33A, K34A, R52A, K60A, R118A, H121A, H122A, H122L, R126A, R128A, R169A, R198A, T36A, H53A, V62A, L88A, W90F, W90A, Y120F, Y120A, H121R, H122R, R126E, W90Y, and 25   R132E as numbered in SEQ ID NO: 1 or one or more corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises a combination of alterations selected from the group consisting of: K34A+R33A, K34A+H122A, K34A+Y120F, K34A+R52A, K34A+H122A, K34A+H121A, W90A+ R126E, W90Y+R126E, H121R+H122R, R126+R132E, W90Y+R132E, and W90Y+R126E+R132E as numbered in SEQ ID NO: 1 or 30 one or more corresponding alterations thereof. In one aspect provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and at least one nucleobase editor domain comprising a cytidine deaminase selected from the group consisting of APOBEC2 family members, 2020216484   17 Mar 2026 APOBEC3 family members, APOBEC4 family members, cytidine deaminase 1 family members (CDA1), A3A family members, RrA3F family members, PmCDA1 family members, and FENRY family members. In some embodiments, the APOBEC3 family member is selected from the group 5 consisting of APOBEC3A, APOBEC3B, APOBEC3C, APOBEC3D, APOBEC3E, APOBEC3F, APOBEC3G, and APOBEC3H. In some embodiments, the APOBEC2 family member is SsAPOBEC2. Provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and at least one nucleobase editor domain comprising an APOBEC1 selected 10 from the group consisting of ppAPOBEC1, AmAPOBEC1 (BEM3.31), ocAPOBEC1, SsAPOBEC2 (BEM3.39), hAPOBEC3A, maAPOBEC1, and mdAPOBEC1. In some embodiments, the cytidine deaminase comprises one or more alterations at positions R15X, R16X, H21X, R30X, R33X, K34X, R52X, K60X, R118X, H121X, H122X, R126X, R128X, R169X, R198X, T36X, H53X, V62X, L88X, W90X, Y120X or R132X as 15 numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof, wherein X is any amino acid. In some embodiments, the one or more alterations are selected from the group consisting of R15A, R16A, H21A, R30A, R33A, K34A, R52A, K60A, R118A, H121A, H122A, H122L, R126A, R128A, R169A, R198A, T36A, H53A, V62A, L88A, W90F, W90A, Y120F, Y120A, H121R, H122R, R126E, W90Y, and R132E as numbered in 20 SEQ ID NO: 1, or one or more corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises a combination of alterations selected from the group consisting of: K34A+R33A, K34A+H122A, K34A+Y120F, K34A+R52A, K34A+H122A, K34A+H121A, W90A+ R126E, W90Y+R126E, H121R+H122R, R126+R132E, W90Y+R132E, and W90Y+R126E+R132E as numbered in SEQ ID NO: 1, or one or more 25 corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises a combination of alterations selected from the group consisting of Y120F and one or more alterations selected from the group consisting of R33A, W90F, K34A, R52A, H122A, and H121A, as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof. In one aspect provided herein is a fusion protein comprising a polynucleotide 30 programmable DNA binding domain and at least one nucleobase editor domain comprising a cytidine deaminase, wherein the cytidine deaminase comprises one or more alterations at positions R15X, R16X, H21X, R30X, R33X, K34X, R52X, K60X, R118X, H121X, H122X, R126X, R128X, R169X, R198X, T36X, H53X, V62X, L88X, W90X, Y120X or R132X as 2020216484   17 Mar 2026 numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof, wherein X is any amino acid. In some embodiments, the cytidine deaminase comprises one or more alterations selected from the group consisting of R15A, R16A, H21A, R30A, R33A, K34A, R52A, 5  K60A, R118A, H121A, H122A, H122L, R126A, R128A, R169A, R198A, T36A, H53A, V62A, L88A, W90F, W90A, Y120F, Y120A, H121R, H122R, R126E, W90Y, and R132E as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises a combination of alterations selected from the group consisting of: K34A+R33A, K34A+H122A, K34A+Y120F, K34A+R52A, 10  K34A+H122A, K34A+H121A, W90A+ R126E, W90Y+R126E, H121R+H122R, R126+R132E, W90Y+R132E, and W90Y+R126E+R132E as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises an alteration at position Y120F and one or more alterations selected from the group consisting of R33A, W90F, K34A, R52A, H122A, and H121A as numbered in SEQ ID 15 NO: 1, or one or more corresponding alterations thereof. In one aspect provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and at least one nucleobase editor domain comprising a cytidine deaminase, wherein the cytidine deaminase comprises one or more alterations at positions Y130X and R28X as numbered in SEQ ID NO: 1, or one or more corresponding 20 alterations thereof, wherein X is any amino acid. In some embodiments, the cytidine deaminase comprises one or more alterations selected from the group consisting of Y130A and R28A, as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises alterations Y130A and R28A. 25          In one aspect provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and at least one nucleobase editor domain comprising a cytidine deaminase, wherein the cytidine deaminase comprises one or more alterations at positions H122X, K34X, R33X, W90X, or R128X as numbered in SEQ ID NO: 1 or one or more corresponding alterations thereof, wherein X is any amino acid. 30          In some embodiments, the cytidine deaminase comprises one or more alterations selected from the group consisting of H122A, K34A, R33A, W90F, W90A, and R128A as numbered in SEQ ID NO: 1 or one or more corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises a combination of alterations selected from 2020216484   17 Mar 2026 the group consisting of: R33A+K34A, W90F+K34A, R33A+K34A+W90F, and R33A+K34A+H122A+W90F as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof. In some embodiments, the cytidine deaminase is selected from the group consisting of APOBEC1, APOBEC2, APOBEC3A, APOBEC3B, APOBEC3C, APOBEC3D, 5 APOBEC3E, APOBEC3F, APOBEC3G, APOBEC3H, APOBEC4, Activation-induced (cytidine) deaminase (AID), hAPOBEC1, rAPOBEC1, ppAPOBEC1, AmAPOBEC1 (BEM3.31), ocAPOBEC1, SsAPOBEC2 (BEM3.39), hAPOBEC3A, maAPOBEC1, mdAPOBEC1, cytidine deaminase 1 (CDA1), hA3A, RrA3F (BEM3.14), PmCDA1, AID (Activation-induced cytidine deaminase; AICDA), hAID, and FENRY. In some 10 embodiments, the cytidine deaminase is APOBEC1. In some embodiments, the cytidine deaminase is rAPOBEC1. In some embodiments, the cytidine deaminase is hAPOBEC3A. In some embodiments, the cytidine deaminase is ppAPOBEC1. In one aspect provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and a cytidine deaminase, wherein the cytidine 15 deaminase comprises an amino acid sequence that has at least 80% identity to amino acid sequence: MTSEKGPSTGDPTLRRRIESWEFDVFYDPRELRKETCLLYEIKWGMSRKIWRSSGKNTTNHVEVNFIKKFT SERRFHSSISCSITWFLSWSPCWECSQAIREFLSQHPGVTLVIYVARLFWHMDQRNRQGLRDLVNSGVTIQ IMRASEYYHCWRNFVNYPPGDEAHWPQYPPLWMMLYALELHCIILSLPPCLKISRRWQNHLAFFRLHLQNC 20   HYQTIPPHILLATGLIHPSVTWR. In one aspect provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and a cytidine deaminase, wherein the cytidine deaminase comprises an amino acid sequence that has at least 80% identity to amino acid sequence: 25 MKPQIRDHRPNPMEAMYPHIFYFHFENLEKAYGRNETWLCFTVEIIKQYLPVPWKKGVFRNQVDPETHCHA EKCFLSWFCNNTLSPKKNYQVTWYTSWSPCPECAGEVAEFLAEHSNVKLTIYTARLYYFWDTDYQEGLRSL SEEGASVEIMDYEDFQYCWENFVYDDGEPFKRWKGLKYNFQSLTRRLREILQ. In one aspect provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and a cytidine deaminase, wherein the cytidine 30 deaminase comprises an amino acid sequence that has at least 80% identity to amino acid sequence: MADSSEKMRGQYISRDTFEKNYKPIDGTKEAHLLCEIKWGKYGKPWLHWCQNQRMNIHAEDYFMNNIFKAK KHPVHCYVTWYLSWSPCADCASKIVKFLEERPYLKLTIYVAQLYYHTEEENRKGLRLLRSKKVIIRVMDIS DYNYCWKVFVSNQNGNEDYWPLQFDPWVKENYSRLLDIFWESKCRSPNPW. 2020216484   17 Mar 2026 In one aspect provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and a cytidine deaminase, wherein the cytidine deaminase comprises an amino acid sequence that has at least 80% identity to amino acid sequence: 5 MDPQRLRQWPGPGPASRGGYGQRPRIRNPEEWFHELSPRTFSFHFRNLRFASGRNRSYICCQVEGKNCFFQ GIFQNQVPPDPPCHAELCFLSWFQSWGLSPDEHYYVTWFISWSPCCECAAKVAQFLEENRNVSLSLSAARL YYFWKSESREGLRRLSDLGAQVGIMSFQDFQHCWNNFVHNLGMPFQPWKKLHKNYQRLVTELKQILREEPA TYGSPQAQGKVRIGSTAAGLRHSHSHTRSEAHLRPNHSSRQHRILNPPREARARTCVLVDASWICYR. In some embodiments, the cytidine deaminase comprises a H122A alteration. 10          In one aspect provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and a cytidine deaminase, wherein the cytidine deaminase is an APOBEC1 deaminase and comprises a H122A alteration. In one aspect provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and a cytidine deaminase, wherein the cytidine 15 deaminase is rAPOBEC1 and comprises one or more alterations selected from the group consisting of R15A, R16A, H21A, R30A, R33A, K34A, R52A, K60A, R118A, H121A, H122A, H122L, R126A, R128A, R169A, R198A, T36A, H53A, V62A, L88A, W90F, W90A, Y120F, Y120A, H121R, H122R, R126E, W90Y, and R132E. In some embodiments, the cytidine deaminase comprises a combination of alterations selected from the group 20 consisting of: K34A+R33A, K34A+H122A, K34A+Y120F, K34A+R52A, K34A+H122A, K34A+H121A, W90A+ R126E, W90Y+R126E, H121R+H122R, R126+R132E, W90Y+R132E, and W90Y+R126E+R132E. In one aspect provided herein is a fusion protein comprising a polynucleotide programmable DNA binding domain and at least one nucleobase editor domain comprising 25 an APOBEC1 selected from the group consisting of ppAPOBEC1, AmAPOBEC1 (BEM3.31), ocAPOBEC1, SsAPOBEC2 (BEM3.39), hAPOBEC3A, maAPOBEC1, and mdAPOBEC1. In some embodiments, the APOBEC1 comprises one or more alterations at positions R15X, R16X, H21X, R30X, R33X, K34X, R52X, K60X, R118X, H121X, H122X, R126X, 30  R128X, R169X, R198X, T36X, H53X, V62X, L88X, W90X, Y120X or R132X as numbered in SEQ ID NO: 1 or one or more corresponding alterations thereof, wherein X is any amino acid. In some embodiments, the one or more alterations are selected from the group consisting of R15A, R16A, H21A, R30A, R33A, K34A, R52A, K60A, R118A, H121A, 2020216484   17 Mar 2026 H122A, H122L, R126A, R128A, R169A, R198A, T36A, H53A, V62A, L88A, W90F, W90A, Y120F, Y120A, H121R, H122R, R126E, W90Y, and R132E as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof. In some embodiments, the APOBEC1 comprises a combination of alterations selected from the group consisting of: 5  K34A+R33A, K34A+H122A, K34A+Y120F, K34A+R52A, K34A+H122A, K34A+H121A, W90A+ R126E, W90Y+R126E, H121R+H122R, R126+R132E, W90Y+R132E, and W90Y+R126E+R132E as numbered in SEQ ID NO: 1 or one or more corresponding alterations thereof. In some embodiments, the APOBEC1 comprises an alteration at Y120F and one or more alterations selected from the group consisting of R33A, W90F, K34A, 10   R52A, H122A, and H121A as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof. In some embodiments, the fusion protein of any one of aspects above, further comprises at least one adenosine deaminase or catalytically active fragments thereof. In some embodiments, the adenosine deaminase is a TadA deaminase. In some embodiments, the 15 TadA deaminase is a modified adenosine deaminase that does not occur in nature. In some embodiments, the fusion protein comprises two adenosine deaminases that are the same or different. In some embodiments, the two adenosine deaminases are capable of forming heterodimers or homodimers. In some embodiments, the two adenosine deaminase domains are a wild-type TadA and TadA7.10. 20          In some embodiments, the adenosine deaminase comprises a deletion of the C terminus beginning at a residue selected from the group consisting of 149, 150, 151, 152, 153, 154, 155, 156, and 157. In some embodiments, the adenosine deaminase is missing 1, 2, 3, 4, 5 ,6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 6, 17, 18, 19, or 20 N-terminal amino acid residues relative to a full-length adenosine deaminase. In some embodiments, the adenosine 25 deaminase is missing 1, 2, 3, 4, 5 ,6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 6, 17, 18, 19, or 20 C-terminal amino acid residues relative to a full-length adenosine deaminase. In some embodiments, the at least one nucleobase editor domain further comprises an abasic nucleobase editor. In some embodiments, the fusion protein of any one of aspects above, further 30 comprises one or more Nuclear Localization Signals (NLS). In some embodiments, the fusion protein comprises an N-terminal NLS and / or a C-terminal NLS. In some embodiments, the NLS is a bipartite NLS. 2020216484   17 Mar 2026 In some embodiments, the polynucleotide programmable DNA binding domain is Cas9. In some embodiments, the polynucleotide programmable DNA binding domain is a Staphylococcus aureus Cas9 (SaCas9), a Streptococcus pyogenes Cas9 (SpCas9), or variants thereof. In some embodiments, the polynucleotide programmable DNA binding domain 5 comprises a nuclease dead Cas9 (dCas9), a Cas9 nickase (nCas9), or a nuclease active Cas9. In some embodiments, the polynucleotide programmable DNA binding domain comprises a catalytic domain capable of cleaving the reverse complement strand of the nucleic acid sequence. In some embodiments, the polynucleotide programmable DNA binding domain does not comprise a catalytic domain capable of cleaving the nucleic acid sequence. 10          In some embodiments, the Cas9 is dCas9. In some embodiments, the Cas9 is a Cas9 nickase (nCas9). In some embodiments, the nCas9 comprises amino acid substitution D10A or a corresponding amino acid substitution thereof. In some embodiments, the fusion protein of any one of aspects above, further comprises one or more Uracil DNA glycosylase inhibitors (UGI). In some embodiments, the one or more UGI is derived from Bacillus 15 subtilis bacteriophage PBS1 and inhibits human UDG activity. In some embodiments, the fusion protein comprises two Uracil DNA glycosylase inhibitors (UGI). In some embodiments, the fusion protein of any one of aspects above, further comprises one or more linkers. In some embodiments, the fusion protein deaminates a nucleobase in a target nucleotide sequence, and wherein the deamination has an increased ratio of in cis to in trans 20 activity (in cis:in trans) as compared to a standard cytidine base editor. In some embodiments, the standard cytidine base editor comprises (i) a polynucleotide programmable DNA binding domain and (ii) an APOBEC cytidine deaminase. In some embodiments, the APOBEC cytidine deaminase of the standard cytidine base 25 editor is a rat APOBEC-1 cytidine deaminase (rAPOBEC-1). In some embodiments, the polynucleotide programmable DNA binding domain of the standard cytidine base editor is a Cas9 nickase. In some embodiments, the standard cytidine base editor comprises a uracil glycosylase inhibitor (UGI) domain. In some embodiments, the standard cytidine base editor is a BE3 or BE4. In some embodiments, the increased ratio of in cis to in trans activity is 30 increased by at least 2, 2.5, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60 fold or more. In some embodiments, the cytidine base editor has at least 50%, 60%, 70%, 80%, 90%, 95%, 100%, 105%, 110%,115%, 120%, or more in cis activity as compared to the standard cytidine base editor. In some embodiments, the cytidine base editor has at least 2, 5, 10, 15, 20, 25, 30, 35, 2020216484   17 Mar 2026 40, 45, 50, 60, or more fold less in trans activity as compared to the standard cytidine base editor. In one aspect provided herein is a polynucleotide molecule encoding the fusion protein of any one of aspects above. In some embodiments, the polynucleotide is codon 5 optimized. Provided herein is an expression vector comprising a polynucleotide molecule described above. In some embodiments, the expression vector is a mammalian expression vector. In some embodiments, the vector is a viral vector selected from the group consisting of adeno-associated virus (AAV), retroviral vector, adenoviral vector, lentiviral vector, 10 Sendai virus vector, and herpesvirus vector. In some embodiments, the vector comprises a promoter. Provided herein is a cell comprising the polynucleotide described above or the vector described above. In some embodiments, the cell is a bacterial cell, plant cell, insect cell, a human cell, or mammalian cell. 15          Provided herein is a molecular complex comprising the fusion protein of any one of aspects above and one or more of a guide RNA sequence, a tracrRNA sequence, or a target DNA sequence. Provided herein a kit comprising the fusion protein of any one of aspects above, the polynucleotide described above, the vector described above, or the molecular complex 20 described above. Provided herein is a method of editing a nucleobase of a nucleic acid sequence, the method comprising contacting a nucleic acid sequence with a base editor comprising: the fusion protein of any one of aspects above and converting a first nucleobase of the DNA sequence to a second nucleobase. In some embodiments, the first nucleobase is cytosine and 25 the second nucleobase is thymidine. Provided herein is a method of editing a nucleobase of a nucleic acid sequence, the method comprising contacting a nucleic acid sequence with a base editor comprising: the fusion protein of any one of aspects above and converting a first nucleobase of the DNA sequence to a second nucleobase. In some embodiments, the first nucleobase is cytosine and 30 the second nucleobase is thymidine or the first nucleobase is adenine and the second nucleobase is guanine. In some embodiments, the method further comprises converting a third to a fourth nucleobase. In some embodiments, the third nucleobase is guanine and the 2020216484   17 Mar 2026 fourth nucleobase is adenine or the third nucleobase is thymine and the fourth nucleobase is cytosine. Provided herein is a method for optimized base editing, the method comprising: contacting a target nucleobase in a target nucleotide sequence with a cytidine base editor 5 comprising (i) a polynucleotide programmable DNA binding domain and (ii) a cytidine deaminase, wherein the cytidine base editor deaminates the target nucleobase with lower spurious deamination in the target nucleotide sequence as compared to a canonical cytidine base editor comprising a rAPOBEC1. In some embodiments, the cytidine base editor deaminates the target nucleobase at higher efficiency as compared to the canonical cytidine 10 base editor. In some embodiments, the canonical cytidine base editor further comprises a uracil glycosylase inhibitor (UGI) domain. In some embodiments, the canonical cytidine base editor is a BE3 or BE4. In some embodiments, the cytidine base editor generates at least 20%, 30%, 50%, 70%, or 90% lower spurious deamination as compared to the canonical cytidine base editor as measured by an in cis / in trans deamination assay. In some 15 embodiments, the cytidine base editor has at least 50%, 60%, 70%, 80%, 90%, 95%, 100%, 105%, 110%,115%, 120%, or more in cis activity as compared to the canonical cytidine base editor. In some embodiments, the cytidine base editor has at least 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, or more fold less in trans activity as compared to the canonical cytidine base editor. In some embodiments, the cytidine deaminase is (a) an APOBEC-1 from Mesocricetus 20 auratus (MaAPOBEC-1), Pongo pygmaeus (PpAPOBEC-1), Oryctolagus cuniculus (OcAPOBEC-1), Monodelphis domestica (MdAPOBEC-1), or Alligator mississippiensis (AmAPOBEC-1), (b) an APOBEC-2 from Pongo pygmaeus (PpAPOBEC-2), Bos taurus (BtAPOBEC-2), or Sus scrofa (SsAPOBEC-2), (c) an APOBEC-4 from Macaca fascicularis (MfAPOBEC-4), (d) an AID from Canis lupus familaris (ClAID) or Bos Taurus (BtAID), (e) 25 a yeast cytosine deaminase (yCD) from Saccharomyces cerevisiae, (f) an APOBEC-3F from Rhinopithecus roxellana (RrA3F), or (g) a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical to any one of (a)-(f). In some embodiments, the cytidine deaminase is an AID from Canis lupus familaris (ClAID), Bos Taurus (BtAID), or a cytidine deaminase having an amino acid sequence that is 30 at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. In some embodiments, the cytidine deaminase is an APOBEC-3F from Rhinopithecus roxellana (RrA3F), or a cytidine deaminase having an amino acid sequence that is at least 80%, 85%, 90%, 95%, 96%, 97%, 98%, or 99% identical thereto. 2020216484   17 Mar 2026 In some embodiments, the cytidine deaminase comprises an alteration selected from the group consisting of R15X, R16X, H21X, R30X, R33X, K34X, R52X, K60X, R118X, H121X, H122X, R126X, R128X, R169X, R198X, T36X, H53X, V62X, L88X, W90X, Y120X, and R132X as numbered in SEQ ID NO: 1 or a corresponding alteration thereof, 5 wherein X is any amino acid. In some embodiments, the cytidine deaminase comprises an alteration selected from the group consisting of R15A, R16A, H21A, R30A, R33A, K34A, R52A, K60A, R118A, H121A, H122A, H122L, R126A, R128A, R169A, R198A, T36A, H53A, V62A, L88A, W90F, W90A, Y120F, Y120A, H121R, H122R, R126E, W90Y, and R132E as numbered in SEQ ID NO: 1 or a corresponding alteration thereof. 10 In some embodiments, the cytidine deaminase comprises a combination of alterations selected from the group consisting of: K34A+R33A, K34A+H122A, K34A+Y120F, K34A+R52A, K34A+H122A, K34A+H121A, W90A+ R126E, W90Y+R126E, H121R+H122R, R126+R132E, W90Y+R132E, and W90Y+R126E+R132E as numbered in SEQ ID NO: 1 or a corresponding combination of alterations thereof. 15          In some embodiments, the cytidine deaminase comprises an alteration at position Y120F and one or more alterations selected from the group consisting of R33A, W90F, K34A, R52A, H122A, and H121A as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof. In some embodiments, the cytidine deaminase comprises an alterations at position Y130X or R28X as numbered in SEQ ID NO: 1 or a corresponding 20 alteration thereof, wherein X is any amino acid. In some embodiments, the cytidine deaminase comprises an Y130A alteration or a R28A alteration as numbered in SEQ ID NO: 1 or a corresponding alteration thereof. In some embodiments, the cytidine deaminase comprises alterations Y130A and R28A as numbered in SEQ ID NO: 1 or corresponding alterations thereof. 25          In some embodiments, the cytidine deaminase comprises an alteration at positions H122X, K34X, R33X, W90X, and R128X as numbered in SEQ ID NO: 1 or a corresponding alterations thereof, wherein X is any amino acid. In some embodiments, the cytidine deaminase comprises an alteration selected from the group consisting of H122A, K34A, R33A, W90F, W90A, and R128A as numbered in SEQ ID NO: 1, or a corresponding 30 alteration thereof. In some embodiments, the cytidine deaminase comprises a combination of alterations selected from the group consisting of: R33A+K34A, W90F+K34A, R33A+K34A+W90F, and R33A+K34A+H122A+W90F as numbered in SEQ ID NO: 1 or a corresponding combination of alterations thereof. 2020216484   17 Mar 2026 In some embodiments, the cytidine deaminase comprises an amino acid sequence that has at least 80% identity to amino acid sequence: MTSEKGPSTGDPTLRRRIESWEFDVFYDPRELRKETCLLYEIKWGMSRKIWRSSGKNTTNHVEVNFIKKFT SERRFHSSISCSITWFLSWSPCWECSQAIREFLSQHPGVTLVIYVARLFWHMDQRNRQGLRDLVNSGVTIQ 5 IMRASEYYHCWRNFVNYPPGDEAHWPQYPPLWMMLYALELHCIILSLPPCLKISRRWQNHLAFFRLHLQNC HYQTIPPHILLATGLIHPSVTWR. In some embodiments, the cytidine deaminase comprises an amino acid sequence that has at least 80% identity to amino acid sequence: 10 MKPQIRDHRPNPMEAMYPHIFYFHFENLEKAYGRNETWLCFTVEIIKQYLPVPWKKGVFRNQVDPETHCHA EKCFLSWFCNNTLSPKKNYQVTWYTSWSPCPECAGEVAEFLAEHSNVKLTIYTARLYYFWDTDYQEGLRSL SEEGASVEIMDYEDFQYCWENFVYDDGEPFKRWKGLKYNFQSLTRRLREILQ. In some embodiments, the cytidine deaminase comprises an amino acid sequence that has at least 80% identity to amino acid sequence: 15 MADSSEKMRGQYISRDTFEKNYKPIDGTKEAHLLCEIKWGKYGKPWLHWCQNQRMNIHAEDYFMNNIFKAK KHPVHCYVTWYLSWSPCADCASKIVKFLEERPYLKLTIYVAQLYYHTEEENRKGLRLLRSKKVIIRVMDIS DYNYCWKVFVSNQNGNEDYWPLQFDPWVKENYSRLLDIFWESKCRSPNPW. In some embodiments, the cytidine deaminase comprises an amino acid sequence that has at least 80% identity to amino acid sequence: 20 MDPQRLRQWPGPGPASRGGYGQRPRIRNPEEWFHELSPRTFSFHFRNLRFASGRNRSYICCQVEGKNCFFQ GIFQNQVPPDPPCHAELCFLSWFQSWGLSPDEHYYVTWFISWSPCCECAAKVAQFLEENRNVSLSLSAARL YYFWKSESREGLRRLSDLGAQVGIMSFQDFQHCWNNFVHNLGMPFQPWKKLHKNYQRLVTELKQILREEPA TYGSPQAQGKVRIGSTAAGLRHSHSHTRSEAHLRPNHSSRQHRILNPPREARARTCVLVDASWICYR. In some embodiments, the cytidine deaminase comprises a H122A alteration. In some 25 embodiments, the contacting is performed in a cell. In some embodiments, the cell is a human cell or a mammalian cell. In some embodiments, the contacting is in vivo or ex vivo. In one aspect provided herein is a cytidine deaminase comprising an amino acid sequence that has at least 80% identity to an amino acid sequence selected from MTSEKGPSTGDPTLRRRIESWEFDVFYDPRELRKETCLLYEIKWGMSRKIWRSSGKNTTNHVEVNFIKKFT 30 SERRFHSSISCSITWFLSWSPCWECSQAIREFLSQHPGVTLVIYVARLFWHMDQRNRQGLRDLVNSGVTIQ IMRASEYYHCWRNFVNYPPGDEAHWPQYPPLWMMLYALELHCIILSLPPCLKISRRWQNHLAFFRLHLQNC HYQTIPPHILLATGLIHPSVTWR; MKPQIRDHRPNPMEAMYPHIFYFHFENLEKAYGRNETWLCFTVEIIKQYLPVPWKKGVFRNQVDPETHCHA EKCFLSWFCNNTLSPKKNYQVTWYTSWSPCPECAGEVAEFLAEHSNVKLTIYTARLYYFWDTDYQEGLRSL 35 SEEGASVEIMDYEDFQYCWENFVYDDGEPFKRWKGLKYNFQSLTRRLREILQ; 2020216484   17 Mar 2026 MADSSEKMRGQYISRDTFEKNYKPIDGTKEAHLLCEIKWGKYGKPWLHWCQNQRMNIHAEDYFMNNIFKAK KHPVHCYVTWYLSWSPCADCASKIVKFLEERPYLKLTIYVAQLYYHTEEENRKGLRLLRSKKVIIRVMDIS DYNYCWKVFVSNQNGNEDYWPLQFDPWVKENYSRLLDIFWESKCRSPNPW; and MDPQRLRQWPGPGPASRGGYGQRPRIRNPEEWFHELSPRTFSFHFRNLRFASGRNRSYICCQVEGKNCFFQ 5 GIFQNQVPPDPPCHAELCFLSWFQSWGLSPDEHYYVTWFISWSPCCECAAKVAQFLEENRNVSLSLSAARL YYFWKSESREGLRRLSDLGAQVGIMSFQDFQHCWNNFVHNLGMPFQPWKKLHKNYQRLVTELKQILREEPA TYGSPQAQGKVRIGSTAAGLRHSHSHTRSEAHLRPNHSSRQHRILNPPREARARTCVLVDASWICYR. The description and examples herein illustrate embodiments of the present disclosure 10 in detail. It is to be understood that this disclosure is not limited to the particular embodiments described herein and as such can vary. Those of skill in the art will recognize that there are numerous variations and modifications of this disclosure, which are encompassed within its scope. The practice of some embodiments disclosed herein employ, unless otherwise 15 indicated, conventional techniques of immunology, biochemistry, chemistry, molecular biology, microbiology, cell biology, genomics and recombinant DNA, which are within the skill of the art. See for example Sambrook and Green, Molecular Cloning: A Laboratory Manual, 4th Edition (2012); the series Current Protocols in Molecular Biology (F. M. Ausubel, et al. eds.); the series Methods In Enzymology (Academic Press, Inc.), PCR 2: A 20 Practical Approach (M.J. MacPherson, B.D. Hames and G.R. Taylor eds. (1995)), Harlow and Lane, eds. (1988) Antibodies, A Laboratory Manual, and Culture of Animal Cells: A Manual of Basic Technique and Specialized Applications, 6th Edition (R.I. Freshney, ed. (2010)). The section headings used herein are for organizational purposes only and are not to 25 be construed as limiting the subject matter described. Although various features of the present disclosure can be described in the context of a single embodiment, the features can also be provided separately or in any suitable combination. Conversely, although the present disclosure can be described herein in the context of separate embodiments for clarity, the present disclosure can also be implemented 30 in a single embodiment. The section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described. The features of the present disclosure are set forth with particularity herein. A better understanding of the features and advantages of the present disclosure will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in 2020216484   17 Mar 2026 which the principles of the disclosure are utilized, and in view of the accompanying drawings as described hereinbelow. Definitions 5            The following definitions supplement those in the art and are directed to the current application and are not to be imputed to any related or unrelated case, e.g., to any commonly owned patent or application. Although any methods and materials similar or equivalent to those described herein can be used in the practice for testing of the present disclosure, the preferred materials and methods are described herein. Accordingly, the terminology used 10 herein is for the purpose of describing particular embodiments only, and is not intended to be limiting. Unless defined otherwise, all technical and scientific terms used herein have the meaning commonly understood by a person skilled in the art to which this disclosure belongs. The following references provide one of skill with a general definition of many of the terms 15 used in this disclosure: Singleton et al., Dictionary of Microbiology and Molecular Biology (2nd ed. 1994); The Cambridge Dictionary of Science and Technology (Walker ed., 1988); The Glossary of Genetics, 5th Ed., R. Rieger et al. (eds.), Springer Verlag (1991); and Hale & Marham, The Harper Collins Dictionary of Biology (1991). In this application, the use of the singular includes the plural unless specifically 20 stated otherwise. It must be noted that, as used in the specification, the singular forms “a,” “an,” and “the” include plural references unless the context clearly dictates otherwise. In this application, the use of “or” means “and / or,” unless stated otherwise, and is understood to be inclusive. Furthermore, use of the term “including” as well as other forms, such as “include,” “includes,” and “included,” is not limiting. 25          As used herein the terms “comprises” and “comprising” are to be construed as being inclusive and open ended rather than exclusive. Specifically, when used in this specification, including the claims, the terms “comprises” and “comprising” and variations thereof mean that the specified features, steps, or components are included. The terms are not to be interpreted to exclude the presence of other features, steps, or components. 30            As used in this specification and claim(s), the words “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements 2020216484   17 Mar 2026 or method steps. It is contemplated that any embodiment discussed in this specification can be implemented with respect to any method or composition of the present disclosure, and vice versa. Furthermore, compositions of the present disclosure can be used to achieve methods of the present disclosure. 5           The term “about” or “approximately” means within an acceptable error range for the particular value as determined by one of ordinary skill in the art, which will depend in part on how the value is measured or determined, i.e., the limitations of the measurement system. For example, “about” can mean within 1 or more than 1 standard deviation, per the practice in the art. Alternatively, “about” can mean a range of up to 20%, up to 10%, up to 5%, or up 10 to 1% of a given value. Alternatively, particularly with respect to biological systems or processes, the term can mean within an order of magnitude, such as within 5-fold or within 2fold, of a value. Where particular values are described in the application and claims, unless otherwise stated the term “about” meaning within an acceptable error range for the particular value should be assumed. 15            Ranges provided herein are understood to be shorthand for all of the values within the range. For example, a range of 1 to 50 is understood to include any number, combination of numbers, or sub-range from the group consisting 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50. 20           Reference in the specification to “some embodiments,” “an embodiment,” “one embodiment” or “other embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least some embodiments, but not necessarily all embodiments, of the present disclosures. By “abasic base editor” is meant an agent capable of excising a nucleobase and 25 inserting a DNA nucleobase (A, T, C, or G). Abasic base editors comprise a nucleic acid glycosylase polypeptide or fragment thereof. In one embodiment, the nucleic acid glycosylase is a mutant human uracil DNA glycosylase comprising an Asp at amino acid 204 (e.g., replacing an Asn at amino acid 204) in the following sequence, or corresponding position in a uracil DNA glycosylase, and having cytosine-DNA glycosylase activity, or 30 active fragment thereof. In one embodiment, the nucleic acid glycosylase is a mutant human uracil DNA glycosylase comprising an Ala, Gly, Cys, or Ser at amino acid 147 (e.g., replacing a Tyr at amino acid 147) in the following sequence, or corresponding position in a uracil DNA glycosylase, and having thymine-DNA glycosylase activity, or an active 2020216484   17 Mar 2026 10 15 fragment thereof. The sequence of exemplary human uracil-DNA glycosylase, isoform 1, follows: 1 mgvfclgpwg Igrklrtpgk gplqllsrlc gdhlqaipak kapagqeepg tppssplsae 61 qldriqrnka aallrlaarn vpvgfgeswk khlsgefgkp yfiklmgfva eerkhytvyp 121 pphqvftwtq mcdikdvkvv ilgqdpyhgp nqahglcfsv qrpvppppsl eniykelstd 181 iedfvhpghg dlsgwakqgv lllnavltvr ahqanshker gweqftdavv swlnqnsngl 241 vfllwgsyaq kkgsaidrkr hhvlqtahps plsvyrgffg crhfsktnel lqksgkkpid 301 wkel The sequence of human uracil-DNA glycosylase, isoform 2, follows: 1 migqktlysf fspsparkrh apspepavqg tgvagvpees gdaaaipakk apagqeepgt 61 ppssplsaeq ldriqrnkaa allrlaarnv pvgfgeswkk hlsgefgkpy fiklmgfvae 121 erkhytvypp phqvftwtqm cdikdvkvvi lgqdpyhgpn qahglcfsvq rpvppppsle 181 niykelstdi edfvhpghgd lsgwakqgvl llnavltvra hqanshkerg weqftdavvs 241 wlnqnsnglv fllwgsyaqk kgsaidrkrh hvlqtahpsp Isvyrgffgc rhfsktnell 301 qksgkkpidw kel In other embodiments, the abasic editor is any one of the abasic editors described in 20   PCT / JP2015 / 080958 and US20170321210, which are incorporated herein by reference. In particular embodiments, the abasic editor comprises a mutation at a position shown in the sequence above in bold with underlining or at a corresponding amino acid in any other abasic editor or uracil deglycosylase known in the art. In one embodiment, the abasic editor comprises a mutation at Y147, N204, L272, and / or R276, or corresponding position. In 25 another embodiment, the abasic editor comprises a Y147A or Y147G mutation, or corresponding mutation. In another embodiment, the abasic editor comprises a N204D mutation, or corresponding mutation. In another embodiment, the abasic editor comprises a L272A mutation, or corresponding mutation. In another embodiment, the abasic editor comprises a R276E or R276C mutation, or corresponding mutation. 30           By “adenosine deaminase” is meant a polypeptide or fragment thereof capable of catalyzing the hydrolytic deamination of adenine or adenosine. In some embodiments, the deaminase or deaminase domain is an adenosine deaminase catalyzing the hydrolytic deamination of adenosine to inosine or deoxy adenosine to deoxyinosine. In some embodiments, the adenosine deaminase catalyzes the hydrolytic deamination of adenine or 35 adenosine in deoxyribonucleic acid (DNA). The adenosine deaminases (e.g., engineered adenosine deaminases, evolved adenosine deaminases) provided herein may be from any organism, such as a bacterium. 2020216484   17 Mar 2026 In some embodiments, the adenosine deaminase is a TadA deaminase. In some embodiments, the TadA deaminase is TadA variant. In some embodiments, the TadA variant is a TadA*7.10. In some embodiments, the deaminase or deaminase domain is a variant of a naturally occurring deaminase from an organism, such as a human, chimpanzee, gorilla, 5 monkey, cow, dog, rat, or mouse. In some embodiments, the deaminase or deaminase domain does not occur in nature. For example, in some embodiments, the deaminase or deaminase domain is at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75% at least 80%, at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.1%, 10 at least 99.2%, at least 99.3%, at least 99.4%, at least 99.5%, at least 99.6%, at least 99.7%, at least 99.8%, or at least 99.9% identical to a naturally occurring deaminase. For example, deaminase domains are described in International PCT Application Nos. PCT / 2017 / 045381 (WO 2018 / 027078) and PCT / US2016 / 058344 (WO 2017 / 070632), each of which is incorporated herein by reference for its entirety. Also, see Komor, A.C., et al., 15 “Programmable editing of a target base in genomic DNA without double-stranded DNA cleavage” Nature 533, 420-424 (2016); Gaudelli, N.M., et al., “Programmable base editing of A»T to G*C in genomic DNA without DNA cleavage” Nature 551, 464-471 (2017); Komor, A.C., et al., “Improved base excision repair inhibition and bacteriophage Mu Gam protein yields C:G-to-T:A base editors with higher efficiency and product purity” Science Advances 20   3:eaao4774 (2017) ), and Rees, H.A., et al., “Base editing: precision chemistry on the genome and transcriptome of living cells.” Nat Rev Genet. 2018 Dec;19(12):770-788. doi: 10.1038 / s41576-018-0059-1, the entire contents of which are hereby incorporated by reference. In some embodiments, the adenosine deaminase comprises an alteration in the 25 following sequence: MSEVEFSHEY WMRHALTLAK RARDEREVPV GAVLVLNNRV IGEGWNRAIG LHDPTAHAEI MALRQGGLVM QNYRLIDATL YVTFEPCVMC AGAMIHSRIG RVVFGVRNAK TGAAGSLMDV LHYPGMNHRV EITEGILADE CAALLCYFFR MPRQVFNAQK KAQSSTD 30 (also termed TadA*7.10). In particular embodiments, an adenosine deaminase heterodimer comprises an TadA*7.10 domain and an adenosine deaminase domain selected from one of the following: Staphylococcus aureus (S. aureus) TadA: 2020216484   17 Mar 2026 MGSHMTNDIYFMTLAIEEAKKAAQLGEVPIGAIITKDDEVIARAHNLRETLQQPTAHAEHIA IERAAKVLGSWRLEGCTLYVTLEPCVMCAGTIVMSRIPRVVYGADDPKGGCSGSLMNLLQQS NFNHRAIVDKGVLKEACSTLLTTFFKNLRANKKSTN Bacillus subtilis (B. subtilis) TadA: 5 MTQDELYMKEAIKEAKKAEEKGEVPIGAVLVINGEIIARAHNLRETEQRSIAHAEMLVIDEA CKALGTWRLEGATLYVTLEPCPMCAGAVVLSRVEKVVFGAFDPKGGCSGTLMNLLQEERFNH QAEVVSGVLEEECGGMLSAFFRELRKKKKAARKNLSE Salmonella typhimurium (S. typhimurium) TadA: MPPAFITGVTSLSDVELDHEYWMRHALTLAKRAWDEREVPVGAVLVHNHRVIGEGWNRPIGR 10 HDPTAHAEIMALRQGGLVLQNYRLLDTTLYVTLEPCVMCAGAMVHSRIGRVVFGARDAKTGA AGSLIDVLHHPGMNHRVEIIEGVLRDECATLLSDFFRMRRQEIKALKKADRAEGAGPAV Shewanella putrefaciens (S. putrefaciens) TadA: MDEYWMQVAMQMAEKAEAAGEVPVGAVLVKDGQQIATGYNLSISQHDPTAHAEILCLRSAGK KLENYRLLDATLYITLEPCAMCAGAMVHSRIARVVYGARDEKTGAAGTVVNLLQHPAFNHQV 15 EVTSGVLAEACSAQLSRFFKRRRDEKKALKLAQRAQQGIE Haemophilus influenzae F3031 (H. influenzae) TadA: MDAAKVRSEFDEKMMRYALELADKAEALGEIPVGAVLVDDARNIIGEGWNLSIVQSDPTAHA EIIALRNGAKNIQNYRLLNSTLYVTLEPCTMCAGAILHSRIKRLVFGASDYKTGAIGSRFHF FDDYKMNHTLEITSGVLAEECSQKLSTFFQKRREEKKIEKALLKSLSDK 20   Caulobacter crescentus (C. crescentus) TadA: MRTDESEDQDHRMMRLALDAARAAAEAGETPVGAVILDPSTGEVIATAGNGPIAAHDPTAHA EIAAMRAAAAKLGNYRLTDLTLVVTLEPCAMCAGAISHARIGRVVFGADDPKGGAVVHGPKF FAQPTCHWRPEVTGGVLADESADLLRGFFRARRKAKI Geobacter sulfurreducens (G. sulfurreducens) TadA: 25 MSSLKKTPIRDDAYWMGKAIREAAKAAARDEVPIGAVIVRDGAVIGRGHNLREGSNDPSAHA EMIAIRQAARRSANWRLTGATLYVTLEPCLMCMGAIILARLERVVFGCYDPKGGAAGSLYDL SADPRLNHQVRLSPGVCQEECGTMLSDFFRDLRRRKKAKATPALFIDERKVPPEP TadA*7.10 MSEVEFSHEYWMRHALTLAKRARDEREVPVGAVLVLNNRVIGEGWNRAIGLHDPTAHAEIMA 30 LRQGGLVMQNYRLIDATLYVTFEPCVMCAGAMIHSRIGRVVFGVRNAKTGAAGSLMDVLHYP GMNHRVEITEGILADECAALLCYFFRMPRQVFNAQKKAQSSTD “Administering” is referred to herein as providing one or more compositions described herein to a patient or a subject. By way of example and without limitation, composition administration, e.g., injection, can be performed by intravenous (i.v.) injection, 2020216484   17 Mar 2026 sub-cutaneous (s.c.) injection, intradermal (i.d.) injection, intraperitoneal (i.p.) injection, or intramuscular (i.m.) injection. One or more such routes can be employed. Parenteral administration can be, for example, by bolus injection or by gradual perfusion over time. In some embodiments, parenteral administration includes infusing or injecting intravascularly, 5 intravenously, intramuscularly, intraarterially, intrathecally, intratumorally, intradermally, intraperitoneally, transtracheally, subcutaneously, subcuticularly, intraarticularly, subcapsularly, subarachnoidly and intrasternally. Alternatively, or concurrently, administration can be by an oral route. By “agent” is meant any small molecule chemical compound, antibody, nucleic acid 10 molecule, or polypeptide, or fragments thereof. By “alteration” is meant a change (e.g. increase or decrease) in the structure, expression levels or activity of a gene or polypeptide as detected by standard art known methods such as those described herein. As used herein, an alteration includes a change in a polynucleotide or polypeptide sequence or a change in expression levels, such as a 10% 15 change, a 25% change, a 40% change, a 50% change, or greater. By “ameliorate” is meant decrease, suppress, attenuate, diminish, arrest, or stabilize the development or progression of a disease. By “analog” is meant a molecule that is not identical, but has analogous functional or structural features. For example, a polynucleotide or polypeptide analog retains the 20 biological activity of a corresponding naturally-occurring polynucleotide or polypeptide, while having certain modifications that enhance the analog's function relative to a naturally occurring polynucleotide or polypeptide. Such modifications could increase the analog's affinity for DNA, efficiency, specificity, protease or nuclease resistance, membrane permeability, and / or half-life, without altering, for example, ligand binding. An analog may 25 include an unnatural nucleotide or amino acid. By "base editor (BE)" or "nucleobase editor (NBE)" is meant an agent that binds a polynucleotide and has nucleobase modifying activity. In various embodiments, the base editor comprises a nucleobase modifying polypeptide (e.g., a deaminase) and a nucleic acid programmable nucleotide binding domain in conjunction with a guide polynucleotide (e.g., 30 guide RNA). In various embodiments, the agent is a biomolecular complex comprising a protein domain having base editing activity, i.e., a domain capable of modifying a base (e.g., A, T, C, G, or U) within a nucleic acid molecule (e.g., DNA). In some embodiments, the polynucleotide programmable DNA binding domain is fused or linked to one or more 2020216484   17 Mar 2026 deaminase domains. In one embodiment, the agent is a fusion protein comprising one or more domains having base editing activity. In another embodiment, the protein domains having base editing activity are linked to the guide RNA (e.g., via an RNA binding motif on the guide RNA and an RNA binding domain fused to the deaminase). In some embodiments, 5 the domains having base editing activity are capable of deaminating a base within a nucleic acid molecule. In some embodiments, the base editor is capable of deaminating one or more bases within a DNA molecule. In some embodiments, the base editor is capable of deaminating a cytosine (C) or an adenosine (A) within DNA. In some embodiments, the base editor is capable of deaminating a cytosine (C) and an adenosine (A) within DNA. In some 10 embodiments, the base editor is capable of deaminating a cytosine (C) within DNA. In some embodiments, the base editor is a cytidine base editor (CBE) (e.g., BE4). In some embodiments, the base editor is capable of deaminating an adenosine (A) within DNA. In some embodiments, the base editor is a standard base editor that comprises naturally occurring protein domains that have base editing activity and / or programmable DNA binding 15 activity. For example, a standard cytidine base editor may contain a cytidine deaminase, e.g. an APOBEC cytidine deaminase or an AID deaminase. In some embodiments, the standard cytidine deaminase contains an APOBEC1 cytidine deaminase, e.g. a rAPOBEC1. In some embodiments, the standard cytidine base editor further comprises additional domains associated or linked to the cytidine deaminase, for example, one or more UGI domains may 20 be linked or to the cytidine deaminase. In some embodiments, the base editor is an adenosine base editor (ABE) and a cytidine base editor (CBE). In some embodiments, the base editor is a nuclease-inactive Cas9 (dCas9) fused to an adenosine deaminase and / or cytidine deaminase. In some embodiments, the Cas9 is a circular permutant Cas9 (e.g., spCas9 or saCas9). Circular permutant Cas9s are known in the 25 art and described, for example, in Oakes et al., Cell 176, 254-267, 2019. In some embodiments, the base editor is fused to an inhibitor of base excision repair, for example, a UGI domain, or a dISN domain. In some embodiments, the fusion protein comprises a Cas9 nickase fused to one or more deaminases and an inhibitor of base excision repair, such as a UGI or dISN domain. In other embodiments the base editor is an abasic base editor. 30          In some embodiments, adenosine base editors are generated by cloning an adenosine deaminase variant into a scaffold that includes a circular permutant Cas9 (e.g., spCAS9 or saCAS9) and a bipartite nuclear localization sequence. Circular permutant Cas9s are known in the art and described, for example, in Oakes et al., Cell 176, 254-267, 2019. Exemplary 2020216484   17 Mar 2026 circular permutants follow where the bold sequence indicates sequence derived from Cas9, the italics sequence denotes a linker sequence, and the underlined sequence denotes a bipartite nuclear localization sequence. CP5 (with MSP “NGC=Pam Variant with mutations Regular Cas9 likes NGG” PID=Protein 5 Interacting Domain and “D10A” nickase): EIGKATAKYFFYSNIMNFFKTEITLANGEIRKRPLIETNGETGEIVWDKGRDFATVRKVLSM PQVNIVKKTEVQTGGFSKESILPKRNSDKLIARKKDWDPKKYGGFMQPTVAYSVLVVAKVEK GKSKKLKSVKELLGITIMERSSFEKNPIDFLEAKGYKEVKKDLIIKLPKYSLFELENGRKRM LASAKFLQKGNELALPSKYVNFLYLASHYEKLKGSPEDNEQKQLFVEQHKHYLDEIIEQISE 10 FSKRVILADANLDKVLSAYNKHRDKPIREQAENIIHLFTLTNLGAPRAFKYFDTTIARKEYR STKEVLDATLIHQSITGLYETRIDLSQLGGDGGSGGSGGSGGSGGSGGSGGMDKKYSIGLAI GTNSVGWAVITDEYKVPSKKFKVLGNTDRHSIKKNLIGALLFDSGETAEATRLKRTARRRYT RRKNRICYLQEIFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFGNIVDEVAYHEKYPTI YHLRKKLVDSTDKADLRLIYLALAHMIKFRGHFLIEGDLNPDNSDVDKLFIQLVQTYNQLFE 15 ENPINASGVDAKAILSARLSKSRRLENLIAQLPGEKKNGLFGNLIALSLGLTPNFKSNFDLA EDAKLQLSKDTYDDDLDNLLAQIGDQYADLFLAAKNLSDAILLSDILRVNTEITKAPLSASM IKRYDEHHQDLTLLKALVRQQLPEKYKEIFFDQSKNGYAGYIDGGASQEEFYKFIKPILEKM DGTEELLVKLNREDLLRKQRTFDNGSIPHQIHLGELHAILRRQEDFYPFLKDNREKIEKILT FRIPYYVGPLARGNSRFAWMTRKSEETITPWNFEEVVDKGASAQSFIERMTNFDKNLPNEKV 20 LPKHSLLYEYFTVYNELTKVKYVTEGMRKPAFLSGEQKKAIVDLLFKTNRKVTVKQLKEDYF KKIECFDSVEISGVEDRFNASLGTYHDLLKIIKDKDFLDNEENEDILEDIVLTLTLFEDREM IEERLKTYAHLFDDKVMKQLKRRRYTGWGRLSRKLINGIRDKQSGKTILDFLKSDGFANRNF MQLIHDDSLTFKEDIQKAQVSGQGDSLHEHIANLAGSPAIKKGILQTVKVVDELVKVMGRHK PENIVIEMARENQTTQKGQKNSRERMKRIEEGIKELGSQILKEHPVENTQLQNEKLYLYYLQ 25 NGRDMYVDQELDINRLSDYDVDHIVPQSFLKDDSIDNKVLTRSDKNRGKSDNVPSEEVVKKM KNYWRQLLNAKLITQRKFDNLTKAERGGLSELDKAGFIKRQLVETRQITKHVAQILDSRMNT KYDENDKLIREVKVITLKSKLVSDFRKDFQFYKVREINNYHHAHDAYLNAVVGTALIKKYPK LESEFVYGDYKVYDVRKMIAKSEQEGADKRTADGSEFESPKKKRKV* . 30         In some embodiments, the polynucleotide programmable DNA binding domain is a CRISPR associated (e.g., Cas or Cpf1) enzyme. In some embodiments, the base editor is a catalytically dead Cas9 (dCas9) fused to one or more deaminase domains. In some embodiments, the base editor is a Cas9 nickase (nCas9) fused to one or more deaminase 2020216484   17 Mar 2026 domains. In some embodiments, the base editor is fused to an inhibitor of base excision repair (BER). In some embodiments, the inhibitor of base excision repair is a uracil DNA glycosylase inhibitor (UGI). In some embodiments, the inhibitor of base excision repair is an inosine base excision repair inhibitor. 5          Details of base editors are described in International PCT Application Nos. PCT / 2017 / 045381 (WO 2018 / 027078) and PCT / US2016 / 058344 (WO 2017 / 070632), each of which is incorporated herein by reference for its entirety. Also see Komor, A.C., et al., “Programmable editing of a target base in genomic DNA without double-stranded DNA cleavage” Nature 533, 420-424 (2016); Gaudelli, N.M., et al., “Programmable base editing of 10 A»T to G»C in genomic DNA without DNA cleavage” Nature 551, 464-471 (2017); Komor, A.C., et al., “Improved base excision repair inhibition and bacteriophage Mu Gam protein yields C:G-to-T:A base editors with higher efficiency and product purity” Science Advances 3:eaao4774 (2017), and Rees, H.A., et al., “Base editing: precision chemistry on the genome and transcriptome of living cells.” Nat Rev Genet. 2018 Dec;19(12):770-788. doi: 15    10.1038 / s41576-018-0059-1, the entire contents of which are hereby incorporated by reference. By way of example, the adenine base editor (ABE) as used in the base editing compositions, systems and methods described herein has the nucleic acid sequence (8877 base pairs), (Addgene, Watertown, MA.; Gaudelli NM, et al., Nature. 2017 Nov 20   23;551(7681):464-471. doi: 10.1038 / nature24644; Koblan LW, et al., Nat Biotechnol. 2018 Oct;36(9):843-846. doi: 10.1038 / nbt.4172.) as provided below. Polynucleotide sequences having at least 95% or greater identity to the ABE nucleic acid sequence are also encompassed. ATATGCCAAGTACGCCCCCTATTGACGTCAATGACGGTAAATGGCCCGCCTGGCATTATGCCCAGTACAT 25 GACCTTATGGGACTTTCCTACTTGGCAGTACATCTACGTATTAGTCATCGCTATTACCATGGTGATGCGG TTTTGGCAGTACATCAATGGGCGTGGATAGCGGTTTGACTCACGGGGATTTCCAAGTCTCCACCCCATTG ACGTCAATGGGAGTTTGTTTTGGCACCAAAATCAACGGGACTTTCCAAAATGTCGTAACAACTCCGCCCC ATTGACGCAAATGGGCGGTAGGCGTGTACGGTGGGAGGTCTATATAAGCAGAGCTGGTTTAGTGAACCGT CAGATCCGCTAGAGATCCGCGGCCGCTAATACGACTCACTATAGGGAGAGCCGCCACCATGAAACGGACA 30 GCCGACGGAAGCGAGTTCGAGTCACCAAAGAAGAAGCGGAAAGTCTCTGAAGTCGAGTTTAGCCACGAGT ATTGGATGAGGCACGCACTGACCCTGGCAAAGCGAGCATGGGATGAAAGAGAAGTCCCCGTGGGCGCCGT GCTGGTGCACAACAATAGAGTGATCGGAGAGGGATGGAACAGGCCAATCGGCCGCCACGACCCTACCGCA CACGCAGAGATCATGGCACTGAGGCAGGGAGGCCTGGTCATGCAGAATTACCGCCTGATCGATGCCACCC TGTATGTGACACTGGAGCCATGCGTGATGTGCGCAGGAGCAATGATCCACAGCAGGATCGGAAGAGTGGT 35 GTTCGGAGCACGGGACGCCAAGACCGGCGCAGCAGGCTCCCTGATGGATGTGCTGCACCACCCCGGCATG 2020216484   17 Mar 2026 AACCACCGGGTGGAGATCACAGAGGGAATCCTGGCAGACGAGTGCGCCGCCCTGCTGAGCGATTTCTTTA GAATGCGGAGACAGGAGATCAAGGCCCAGAAGAAGGCACAGAGCTCCACCGACTCTGGAGGATCTAGCGG AGGATCCTCTGGAAGCGAGACACCAGGCACAAGCGAGTCCGCCACACCAGAGAGCTCCGGCGGCTCCTCC GGAGGATCCTCTGAGGTGGAGTTTTCCCACGAGTACTGGATGAGACATGCCCTGACCCTGGCCAAGAGGG 5 CACGCGATGAGAGGGAGGTGCCTGTGGGAGCCGTGCTGGTGCTGAACAATAGAGTGATCGGCGAGGGCTG GAACAGAGCCATCGGCCTGCACGACCCAACAGCCCATGCCGAAATTATGGCCCTGAGACAGGGCGGCCTG GTCATGCAGAACTACAGACTGATTGACGCCACCCTGTACGTGACATTCGAGCCTTGCGTGATGTGCGCCG GCGCCATGATCCACTCTAGGATCGGCCGCGTGGTGTTTGGCGTGAGGAACGCAAAAACCGGCGCCGCAGG CTCCCTGATGGACGTGCTGCACTACCCCGGCATGAATCACCGCGTCGAAATTACCGAGGGAATCCTGGCA 10 GATGAATGTGCCGCCCTGCTGTGCTATTTCTTTCGGATGCCTAGACAGGTGTTCAATGCTCAGAAGAAGG CCCAGAGCTCCACCGACTCCGGAGGATCTAGCGGAGGCTCCTCTGGCTCTGAGACACCTGGCACAAGCGA GAGCGCAACACCTGAAAGCAGCGGGGGCAGCAGCGGGGGGTCAGACAAGAAGTACAGCATCGGCCTGGCC ATCGGCACCAACTCTGTGGGCTGGGCCGTGATCACCGACGAGTACAAGGTGCCCAGCAAGAAATTCAAGG TGCTGGGCAACACCGACCGGCACAGCATCAAGAAGAACCTGATCGGAGCCCTGCTGTTCGACAGCGGCGA 15 AACAGCCGAGGCCACCCGGCTGAAGAGAACCGCCAGAAGAAGATACACCAGACGGAAGAACCGGATCTGC TATCTGCAAGAGATCTTCAGCAACGAGATGGCCAAGGTGGACGACAGCTTCTTCCACAGACTGGAAGAGT CCTTCCTGGTGGAAGAGGATAAGAAGCACGAGCGGCACCCCATCTTCGGCAACATCGTGGACGAGGTGGC CTACCACGAGAAGTACCCCACCATCTACCACCTGAGAAAGAAACTGGTGGACAGCACCGACAAGGCCGAC CTGCGGCTGATCTATCTGGCCCTGGCCCACATGATCAAGTTCCGGGGCCACTTCCTGATCGAGGGCGACC 20 TGAACCCCGACAACAGCGACGTGGACAAGCTGTTCATCCAGCTGGTGCAGACCTACAACCAGCTGTTCGA GGAAAACCCCATCAACGCCAGCGGCGTGGACGCCAAGGCCATCCTGTCTGCCAGACTGAGCAAGAGCAGA CGGCTGGAAAATCTGATCGCCCAGCTGCCCGGCGAGAAGAAGAATGGCCTGTTCGGAAACCTGATTGCCC TGAGCCTGGGCCTGACCCCCAACTTCAAGAGCAACTTCGACCTGGCCGAGGATGCCAAACTGCAGCTGAG CAAGGACACCTACGACGACGACCTGGACAACCTGCTGGCCCAGATCGGCGACCAGTACGCCGACCTGTTT 25 CTGGCCGCCAAGAACCTGTCCGACGCCATCCTGCTGAGCGACATCCTGAGAGTGAACACCGAGATCACCA AGGCCCCCCTGAGCGCCTCTATGATCAAGAGATACGACGAGCACCACCAGGACCTGACCCTGCTGAAAGC TCTCGTGCGGCAGCAGCTGCCTGAGAAGTACAAAGAGATTTTCTTCGACCAGAGCAAGAACGGCTACGCC GGCTACATTGACGGCGGAGCCAGCCAGGAAGAGTTCTACAAGTTCATCAAGCCCATCCTGGAAAAGATGG ACGGCACCGAGGAACTGCTCGTGAAGCTGAACAGAGAGGACCTGCTGCGGAAGCAGCGGACCTTCGACAA 30 CGGCAGCATCCCCCACCAGATCCACCTGGGAGAGCTGCACGCCATTCTGCGGCGGCAGGAAGATTTTTAC CCATTCCTGAAGGACAACCGGGAAAAGATCGAGAAGATCCTGACCTTCCGCATCCCCTACTACGTGGGCC CTCTGGCCAGGGGAAACAGCAGATTCGCCTGGATGACCAGAAAGAGCGAGGAAACCATCACCCCCTGGAA CTTCGAGGAAGTGGTGGACAAGGGCGCTTCCGCCCAGAGCTTCATCGAGCGGATGACCAACTTCGATAAG AACCTGCCCAACGAGAAGGTGCTGCCCAAGCACAGCCTGCTGTACGAGTACTTCACCGTGTATAACGAGC 35 TGACCAAAGTGAAATACGTGACCGAGGGAATGAGAAAGCCCGCCTTCCTGAGCGGCGAGCAGAAAAAGGC CATCGTGGACCTGCTGTTCAAGACCAACCGGAAAGTGACCGTGAAGCAGCTGAAAGAGGACTACTTCAAG AAAATCGAGTGCTTCGACTCCGTGGAAATCTCCGGCGTGGAAGATCGGTTCAACGCCTCCCTGGGCACAT ACCACGATCTGCTGAAAATTATCAAGGACAAGGACTTCCTGGACAATGAGGAAAACGAGGACATTCTGGA AGATATCGTGCTGACCCTGACACTGTTTGAGGACAGAGAGATGATCGAGGAACGGCTGAAAACCTATGCC 40 CACCTGTTCGACGACAAAGTGATGAAGCAGCTGAAGCGGCGGAGATACACCGGCTGGGGCAGGCTGAGCC GGAAGCTGATCAACGGCATCCGGGACAAGCAGTCCGGCAAGACAATCCTGGATTTCCTGAAGTCCGACGG 2020216484   17 Mar 2026 CTTCGCCAACAGAAACTTCATGCAGCTGATCCACGACGACAGCCTGACCTTTAAAGAGGACATCCAGAAA GCCCAGGTGTCCGGCCAGGGCGATAGCCTGCACGAGCACATTGCCAATCTGGCCGGCAGCCCCGCCATTA AGAAGGGCATCCTGCAGACAGTGAAGGTGGTGGACGAGCTCGTGAAAGTGATGGGCCGGCACAAGCCCGA GAACATCGTGATCGAAATGGCCAGAGAGAACCAGACCACCCAGAAGGGACAGAAGAACAGCCGCGAGAGA 5 ATGAAGCGGATCGAAGAGGGCATCAAAGAGCTGGGCAGCCAGATCCTGAAAGAACACCCCGTGGAAAACA CCCAGCTGCAGAACGAGAAGCTGTACCTGTACTACCTGCAGAATGGGCGGGATATGTACGTGGACCAGGA ACTGGACATCAACCGGCTGTCCGACTACGATGTGGACCATATCGTGCCTCAGAGCTTTCTGAAGGACGAC TCCATCGACAACAAGGTGCTGACCAGAAGCGACAAGAACCGGGGCAAGAGCGACAACGTGCCCTCCGAAG AGGTCGTGAAGAAGATGAAGAACTACTGGCGGCAGCTGCTGAACGCCAAGCTGATTACCCAGAGAAAGTT 10 CGACAATCTGACCAAGGCCGAGAGAGGCGGCCTGAGCGAACTGGATAAGGCCGGCTTCATCAAGAGACAG CTGGTGGAAACCCGGCAGATCACAAAGCACGTGGCACAGATCCTGGACTCCCGGATGAACACTAAGTACG ACGAGAATGACAAGCTGATCCGGGAAGTGAAAGTGATCACCCTGAAGTCCAAGCTGGTGTCCGATTTCCG GAAGGATTTCCAGTTTTACAAAGTGCGCGAGATCAACAACTACCACCACGCCCACGACGCCTACCTGAAC GCCGTCGTGGGAACCGCCCTGATCAAAAAGTACCCTAAGCTGGAAAGCGAGTTCGTGTACGGCGACTACA 15 AGGTGTACGACGTGCGGAAGATGATCGCCAAGAGCGAGCAGGAAATCGGCAAGGCTACCGCCAAGTACTT CTTCTACAGCAACATCATGAACTTTTTCAAGACCGAGATTACCCTGGCCAACGGCGAGATCCGGAAGCGG CCTCTGATCGAGACAAACGGCGAAACCGGGGAGATCGTGTGGGATAAGGGCCGGGATTTTGCCACCGTGC GGAAAGTGCTGAGCATGCCCCAAGTGAATATCGTGAAAAAGACCGAGGTGCAGACAGGCGGCTTCAGCAA AGAGTCTATCCTGCCCAAGAGGAACAGCGATAAGCTGATCGCCAGAAAGAAGGACTGGGACCCTAAGAAG 20 TACGGCGGCTTCGACAGCCCCACCGTGGCCTATTCTGTGCTGGTGGTGGCCAAAGTGGAAAAGGGCAAGT CCAAGAAACTGAAGAGTGTGAAAGAGCTGCTGGGGATCACCATCATGGAAAGAAGCAGCTTCGAGAAGAA TCCCATCGACTTTCTGGAAGCCAAGGGCTACAAAGAAGTGAAAAAGGACCTGATCATCAAGCTGCCTAAG TACTCCCTGTTCGAGCTGGAAAACGGCCGGAAGAGAATGCTGGCCTCTGCCGGCGAACTGCAGAAGGGAA ACGAACTGGCCCTGCCCTCCAAATATGTGAACTTCCTGTACCTGGCCAGCCACTATGAGAAGCTGAAGGG 25 CTCCCCCGAGGATAATGAGCAGAAACAGCTGTTTGTGGAACAGCACAAGCACTACCTGGACGAGATCATC GAGCAGATCAGCGAGTTCTCCAAGAGAGTGATCCTGGCCGACGCTAATCTGGACAAAGTGCTGTCCGCCT ACAACAAGCACCGGGATAAGCCCATCAGAGAGCAGGCCGAGAATATCATCCACCTGTTTACCCTGACCAA TCTGGGAGCCCCTGCCGCCTTCAAGTACTTTGACACCACCATCGACCGGAAGAGGTACACCAGCACCAAA GAGGTGCTGGACGCCACCCTGATCCACCAGAGCATCACCGGCCTGTACGAGACACGGATCGACCTGTCTC 30 AGCTGGGAGGTGACTCTGGCGGCTCAAAAAGAACCGCCGACGGCAGCGAATTCGAGCCCAAGAAGAAGAG GAAAGTCTAACCGGTCATCATCACCATCACCATTGAGTTTAAACCCGCTGATCAGCCTCGACTGTGCCTT CTAGTTGCCAGCCATCTGTTGTTTGCCCCTCCCCCGTGCCTTCCTTGACCCTGGAAGGTGCCACTCCCAC TGTCCTTTCCTAATAAAATGAGGAAATTGCATCGCATTGTCTGAGTAGGTGTCATTCTATTCTGGGGGGT GGGGTGGGGCAGGACAGCAAGGGGGAGGATTGGGAAGACAATAGCAGGCATGCTGGGGATGCGGTGGGCT 35 CTATGGCTTCTGAGGCGGAAAGAACCAGCTGGGGCTCGATACCGTCGACCTCTAGCTAGAGCTTGGCGTA ATCATGGTCATAGCTGTTTCCTGTGTGAAATTGTTATCCGCTCACAATTCCACACAACATACGAGCCGGA AGCATAAAGTGTAAAGCCTAGGGTGCCTAATGAGTGAGCTAACTCACATTAATTGCGTTGCGCTCACTGC CCGCTTTCCAGTCGGGAAACCTGTCGTGCCAGCTGCATTAATGAATCGGCCAACGCGCGGGGAGAGGCGG TTTGCGTATTGGGCGCTCTTCCGCTTCCTCGCTCACTGACTCGCTGCGCTCGGTCGTTCGGCTGCGGCGA 40 GCGGTATCAGCTCACTCAAAGGCGGTAATACGGTTATCCACAGAATCAGGGGATAACGCAGGAAAGAACA TGTGAGCAAAAGGCCAGCAAAAGGCCAGGAACCGTAAAAAGGCCGCGTTGCTGGCGTTTTTCCATAGGCT 2020216484   17 Mar 2026 CCGCCCCCCTGACGAGCATCACAAAAATCGACGCTCAAGTCAGAGGTGGCGAAACCCGACAGGACTATAA AGATACCAGGCGTTTCCCCCTGGAAGCTCCCTCGTGCGCTCTCCTGTTCCGACCCTGCCGCTTACCGGAT ACCTGTCCGCCTTTCTCCCTTCGGGAAGCGTGGCGCTTTCTCATAGCTCACGCTGTAGGTATCTCAGTTC GGTGTAGGTCGTTCGCTCCAAGCTGGGCTGTGTGCACGAACCCCCCGTTCAGCCCGACCGCTGCGCCTTA 5 TCCGGTAACTATCGTCTTGAGTCCAACCCGGTAAGACACGACTTATCGCCACTGGCAGCAGCCACTGGTA ACAGGATTAGCAGAGCGAGGTATGTAGGCGGTGCTACAGAGTTCTTGAAGTGGTGGCCTAACTACGGCTA CACTAGAAGAACAGTATTTGGTATCTGCGCTCTGCTGAAGCCAGTTACCTTCGGAAAAAGAGTTGGTAGC TCTTGATCCGGCAAACAAACCACCGCTGGTAGCGGTGGTTTTTTTGTTTGCAAGCAGCAGATTACGCGCA GAAAAAAAGGATCTCAAGAAGATCCTTTGATCTTTTCTACGGGGTCTGACACTCAGTGGAACGAAAACTC 10 ACGTTAAGGGATTTTGGTCATGAGATTATCAAAAAGGATCTTCACCTAGATCCTTTTAAATTAAAAATGA AGTTTTAAATCAATCTAAAGTATATATGAGTAAACTTGGTCTGACAGTTACCAATGCTTAATCAGTGAGG CACCTATCTCAGCGATCTGTCTATTTCGTTCATCCATAGTTGCCTGACTCCCCGTCGTGTAGATAACTAC GATACGGGAGGGCTTACCATCTGGCCCCAGTGCTGCAATGATACCGCGAGACCCACGCTCACCGGCTCCA GATTTATCAGCAATAAACCAGCCAGCCGGAAGGGCCGAGCGCAGAAGTGGTCCTGCAACTTTATCCGCCT 15 CCATCCAGTCTATTAATTGTTGCCGGGAAGCTAGAGTAAGTAGTTCGCCAGTTAATAGTTTGCGCAACGT TGTTGCCATTGCTACAGGCATCGTGGTGTCACGCTCGTCGTTTGGTATGGCTTCATTCAGCTCCGGTTCC CAACGATCAAGGCGAGTTACATGATCCCCCATGTTGTGCAAAAAAGCGGTTAGCTCCTTCGGTCCTCCGA TCGTTGTCAGAAGTAAGTTGGCCGCAGTGTTATCACTCATGGTTATGGCAGCACTGCATAATTCTCTTAC TGTCATGCCATCCGTAAGATGCTTTTCTGTGACTGGTGAGTACTCAACCAAGTCATTCTGAGAATAGTGT 20 ATGCGGCGACCGAGTTGCTCTTGCCCGGCGTCAATACGGGATAATACCGCGCCACATAGCAGAACTTTAA AAGTGCTCATCATTGGAAAACGTTCTTCGGGGCGAAAACTCTCAAGGATCTTACCGCTGTTGAGATCCAG TTCGATGTAACCCACTCGTGCACCCAACTGATCTTCAGCATCTTTTACTTTCACCAGCGTTTCTGGGTGA GCAAAAACAGGAAGGCAAAATGCCGCAAAAAAGGGAATAAGGGCGACACGGAAATGTTGAATACTCATAC TCTTCCTTTTTCAATATTATTGAAGCATTTATCAGGGTTATTGTCTCATGAGCGGATACATATTTGAATG 25 TATTTAGAAAAATAAACAAATAGGGGTTCCGCGCACATTTCCCCGAAAAGTGCCACCTGACGTCGACGGA TCGGGAGATCGATCTCCCGATCCCCTAGGGTCGACTCTCAGTACAATCTGCTCTGATGCCGCATAGTTAA GCCAGTATCTGCTCCCTGCTTGTGTGTTGGAGGTCGCTGAGTAGTGCGCGAGCAAAATTTAAGCTACAAC AAGGCAAGGCTTGACCGACAATTGCATGAAGAATCTGCTTAGGGTTAGGCGTTTTGCGCTGCTTCGCGAT GTACGGGCCAGATATACGCGTTGACATTGATTATTGACTAGTTATTAATAGTAATCAATTACGGGGTCAT 30 TAGTTCATAGCCCATATATGGAGTTCCGCGTTACATAACTTACGGTAAATGGCCCGCCTGGCTGACCGCC CAACGACCCCCGCCCATTGACGTCAATAATGACGTATGTTCCCATAGTAACGCCAATAGGGACTTTCCAT TGACGTCAATGGGTGGAGTATTTACGGTAAACTGCCCACTTGGCAGTACATCAAGTGTATC By way of example, a cytidine base editor (CBE) as used in the base editing compositions, systems and methods described herein has the following nucleic acid sequence 35   (8877 base pairs), (Addgene, Watertown, MA.; Komor AC, et al., 2017, Sci Adv., 30;3(8):eaao4774. doi: 10.1126 / sciadv.aao4774) as provided below. Polynucleotide sequences having at least 95% or greater identity to the BE4 nucleic acid sequence are also encompassed. 1 ATATGCCAAG TACGCCCCCT ATTGACGTCA ATGACGGTAA ATGGCCCGCC TGGCATTATG 2020216484   17 Mar 2026 61 CCCAGTACAT GACCTTATGG GACTTTCCTA CTTGGCAGTA CATCTACGTA TTAGTCATCG 121 CTATTACCAT GGTGATGCGG TTTTGGCAGT ACATCAATGG GCGTGGATAG CGGTTTGACT 181 CACGGGGATT TCCAAGTCTC CACCCCATTG ACGTCAATGG GAGTTTGTTT TGGCACCAAA 241 ATCAACGGGA CTTTCCAAAA TGTCGTAACA ACTCCGCCCC ATTGACGCAA ATGGGCGGTA 5   301 GGCGTGTACG GTGGGAGGTC TATATAAGCA GAGCTGGTTT AGTGAACCGT CAGATCCGCT 361 AGAGATCCGC GGCCGCTAAT ACGACTCACT ATAGGGAGAG CCGCCACCAT GAGCTCAGAG 421 ACTGGCCCAG TGGCTGTGGA CCCCACATTG AGACGGCGGA TCGAGCCCCA TGAGTTTGAG 481 GTATTCTTCG ATCCGAGAGA GCTCCGCAAG GAGACCTGCC TGCTTTACGA AATTAATTGG 541 GGGGGCCGGC ACTCCATTTG GCGACATACA TCACAGAACA CTAACAAGCA CGTCGAAGTC 10   601 AACTTCATCG AGAAGTTCAC GACAGAAAGA TATTTCTGTC CGAACACAAG GTGCAGCATT 661 ACCTGGTTTC TCAGCTGGAG CCCATGCGGC GAATGTAGTA GGGCCATCAC TGAATTCCTG 721 TCAAGGTATC CCCACGTCAC TCTGTTTATT TACATCGCAA GGCTGTACCA CCACGCTGAC 781 CCCCGCAATC GACAAGGCCT GCGGGATTTG ATCTCTTCAG GTGTGACTAT CCAAATTATG 841 ACTGAGCAGG AGTCAGGATA CTGCTGGAGA AACTTTGTGA ATTATAGCCC GAGTAATGAA 15   901 GCCCACTGGC CTAGGTATCC CCATCTGTGG GTACGACTGT ACGTTCTTGA ACTGTACTGC 961 ATCATACTGG GCCTGCCTCC TTGTCTCAAC ATTCTGAGAA GGAAGCAGCC ACAGCTGACA 1021 TTCTTTACCA TCGCTCTTCA GTCTTGTCAT TACCAGCGAC TGCCCCCACA CATTCTCTGG 1081 GCCACCGGGT TGAAATCTGG TGGTTCTTCT GGTGGTTCTA GCGGCAGCGA GACTCCCGGG 1141 ACCTCAGAGT CCGCCACACC CGAAAGTTCT GGTGGTTCTT CTGGTGGTTC TGATAAAAAG 20   1201 TATTCTATTG GTTTAGCCAT CGGCACTAAT TCCGTTGGAT GGGCTGTCAT AACCGATGAA 1261 TACAAAGTAC CTTCAAAGAA ATTTAAGGTG TTGGGGAACA CAGACCGTCA TTCGATTAAA 1321 AAGAATCTTA TCGGTGCCCT CCTATTCGAT AGTGGCGAAA CGGCAGAGGC GACTCGCCTG 1381 AAACGAACCG CTCGGAGAAG GTATACACGT CGCAAGAACC GAATATGTTA CTTACAAGAA 1441 ATTTTTAGCA ATGAGATGGC CAAAGTTGAC GATTCTTTCT TTCACCGTTT GGAAGAGTCC 25   1501 TTCCTTGTCG AAGAGGACAA GAAACATGAA CGGCACCCCA TCTTTGGAAA CATAGTAGAT 1561 GAGGTGGCAT ATCATGAAAA GTACCCAACG ATTTATCACC TCAGAAAAAA GCTAGTTGAC 1621 TCAACTGATA AAGCGGACCT GAGGTTAATC TACTTGGCTC TTGCCCATAT GATAAAGTTC 1681 CGTGGGCACT TTCTCATTGA GGGTGATCTA AATCCGGACA ACTCGGATGT CGACAAACTG 1741 TTCATCCAGT TAGTACAAAC CTATAATCAG TTGTTTGAAG AGAACCCTAT AAATGCAAGT 30   1801 GGCGTGGATG CGAAGGCTAT TCTTAGCGCC CGCCTCTCTA AATCCCGACG GCTAGAAAAC 1861 CTGATCGCAC AATTACCCGG AGAGAAGAAA AATGGGTTGT TCGGTAACCT TATAGCGCTC 1921 TCACTAGGCC TGACACCAAA TTTTAAGTCG AACTTCGACT TAGCTGAAGA TGCCAAATTG 1981 CAGCTTAGTA AGGACACGTA CGATGACGAT CTCGACAATC TACTGGCACA AATTGGAGAT 2041 CAGTATGCGG ACTTATTTTT GGCTGCCAAA AACCTTAGCG ATGCAATCCT CCTATCTGAC 35   2101 ATACTGAGAG TTAATACTGA GATTACCAAG GCGCCGTTAT CCGCTTCAAT GATCAAAAGG 2161 TACGATGAAC ATCACCAAGA CTTGACACTT CTCAAGGCCC TAGTCCGTCA GCAACTGCCT 2221 GAGAAATATA AGGAAATATT CTTTGATCAG TCGAAAAACG GGTACGCAGG TTATATTGAC 2281 GGCGGAGCGA GTCAAGAGGA ATTCTACAAG TTTATCAAAC CCATATTAGA GAAGATGGAT 2341 GGGACGGAAG AGTTGCTTGT AAAACTCAAT CGCGAAGATC TACTGCGAAA GCAGCGGACT 40   2401 TTCGACAACG GTAGCATTCC ACATCAAATC CACTTAGGCG AATTGCATGC TATACTTAGA 2461 AGGCAGGAGG ATTTTTATCC GTTCCTCAAA GACAATCGTG AAAAGATTGA GAAAATCCTA 2020216484   17 Mar 2026 2521 ACCTTTCGCA TACCTTACTA TGTGGGACCC CTGGCCCGAG GGAACTCTCG GTTCGCATGG 2581 ATGACAAGAA AGTCCGAAGA AACGATTACT CCATGGAATT TTGAGGAAGT TGTCGATAAA 2641 GGTGCGTCAG CTCAATCGTT CATCGAGAGG ATGACCAACT TTGACAAGAA TTTACCGAAC 2701 GAAAAAGTAT TGCCTAAGCA CAGTTTACTT TACGAGTATT TCACAGTGTA CAATGAACTC 5   2761 ACGAAAGTTA AGTATGTCAC TGAGGGCATG CGTAAACCCG CCTTTCTAAG CGGAGAACAG 2821 AAGAAAGCAA TAGTAGATCT GTTATTCAAG ACCAACCGCA AAGTGACAGT TAAGCAATTG 2881 AAAGAGGACT ACTTTAAGAA AATTGAATGC TTCGATTCTG TCGAGATCTC CGGGGTAGAA 2941 GATCGATTTA ATGCGTCACT TGGTACGTAT CATGACCTCC TAAAGATAAT TAAAGATAAG 3001 GACTTCCTGG ATAACGAAGA GAATGAAGAT ATCTTAGAAG ATATAGTGTT GACTCTTACC 10   3061 CTCTTTGAAG ATCGGGAAAT GATTGAGGAA AGACTAAAAA CATACGCTCA CCTGTTCGAC 3121 GATAAGGTTA TGAAACAGTT AAAGAGGCGT CGCTATACGG GCTGGGGACG ATTGTCGCGG 3181 AAACTTATCA ACGGGATAAG AGACAAGCAA AGTGGTAAAA CTATTCTCGA TTTTCTAAAG 3241 AGCGACGGCT TCGCCAATAG GAACTTTATG CAGCTGATCC ATGATGACTC TTTAACCTTC 3301 AAAGAGGATA TACAAAAGGC ACAGGTTTCC GGACAAGGGG ACTCATTGCA CGAACATATT 15   3361 GCGAATCTTG CTGGTTCGCC AGCCATCAAA AAGGGCATAC TCCAGACAGT CAAAGTAGTG 3421 GATGAGCTAG TTAAGGTCAT GGGACGTCAC AAACCGGAAA ACATTGTAAT CGAGATGGCA 3481 CGCGAAAATC AAACGACTCA GAAGGGGCAA AAAAACAGTC GAGAGCGGAT GAAGAGAATA 3541 GAAGAGGGTA TTAAAGAACT GGGCAGCCAG ATCTTAAAGG AGCATCCTGT GGAAAATACC 3601 CAATTGCAGA ACGAGAAACT TTACCTCTAT TACCTACAAA ATGGAAGGGA CATGTATGTT 20   3661 GATCAGGAAC TGGACATAAA CCGTTTATCT GATTACGACG TCGATCACAT TGTACCCCAA 3721 TCCTTTTTGA AGGACGATTC AATCGACAAT AAAGTGCTTA CACGCTCGGA TAAGAACCGA 3781 GGGAAAAGTG ACAATGTTCC AAGCGAGGAA GTCGTAAAGA AAATGAAGAA CTATTGGCGG 3841 CAGCTCCTAA ATGCGAAACT GATAACGCAA AGAAAGTTCG ATAACTTAAC TAAAGCTGAG 3901 AGGGGTGGCT TGTCTGAACT TGACAAGGCC GGATTTATTA AACGTCAGCT CGTGGAAACC 25   3961 CGCCAAATCA CAAAGCATGT TGCACAGATA CTAGATTCCC GAATGAATAC GAAATACGAC 4021 GAGAACGATA AGCTGATTCG GGAAGTCAAA GTAATCACTT TAAAGTCAAA ATTGGTGTCG 4081 GACTTCAGAA AGGATTTTCA ATTCTATAAA GTTAGGGAGA TAAATAACTA CCACCATGCG 4141 CACGACGCTT ATCTTAATGC CGTCGTAGGG ACCGCACTCA TTAAGAAATA CCCGAAGCTA 4201 GAAAGTGAGT TTGTGTATGG TGATTACAAA GTTTATGACG TCCGTAAGAT GATCGCGAAA 30   4261 AGCGAACAGG AGATAGGCAA GGCTACAGCC AAATACTTCT TTTATTCTAA CATTATGAAT 4321 TTCTTTAAGA CGGAAATCAC TCTGGCAAAC GGAGAGATAC GCAAACGACC TTTAATTGAA 4381 ACCAATGGGG AGACAGGTGA AATCGTATGG GATAAGGGCC GGGACTTCGC GACGGTGAGA 4441 AAAGTTTTGT CCATGCCCCA AGTCAACATA GTAAAGAAAA CTGAGGTGCA GACCGGAGGG 4501 TTTTCAAAGG AATCGATTCT TCCAAAAAGG AATAGTGATA AGCTCATCGC TCGTAAAAAG 35   4561 GACTGGGACC CGAAAAAGTA CGGTGGCTTC GATAGCCCTA CAGTTGCCTA TTCTGTCCTA 4621 GTAGTGGCAA AAGTTGAGAA GGGAAAATCC AAGAAACTGA AGTCAGTCAA AGAATTATTG 4681 GGGATAACGA TTATGGAGCG CTCGTCTTTT GAAAAGAACC CCATCGACTT CCTTGAGGCG 4741 AAAGGTTACA AGGAAGTAAA AAAGGATCTC ATAATTAAAC TACCAAAGTA TAGTCTGTTT 4801 GAGTTAGAAA ATGGCCGAAA ACGGATGTTG GCTAGCGCCG GAGAGCTTCA AAAGGGGAAC 40   4861 GAACTCGCAC TACCGTCTAA ATACGTGAAT TTCCTGTATT TAGCGTCCCA TTACGAGAAG 4921 TTGAAAGGTT CACCTGAAGA TAACGAACAG AAGCAACTTT TTGTTGAGCA GCACAAACAT 2020216484   17 Mar 2026 4981 TATCTCGACG AAATCATAGA GCAAATTTCG GAATTCAGTA AGAGAGTCAT 5041 GCCAATCTGG ACAAAGTATT AAGCGCATAC AACAAGCACA GGGATAAACC 5101 CAGGCGGAAA ATATTATCCA TTTGTTTACT CTTACCAACC TCGGCGCTCC 5161 AAGTATTTTG ACACAACGAT AGATCGCAAA CGATACACTT CTACCAAGGA 5   5221 GCGACACTGA TTCACCAATC CATCACGGGA TTATATGAAA CTCGGATAGA 5281 CTTGGGGGTG ACTCTGGTGG TTCTGGAGGA TCTGGTGGTT CTACTAATCT 5341 ATTGAAAAGG AGACCGGTAA GCAACTGGTT ATCCAGGAAT CCATCCTCAT 5401 GAGGTGGAAG AAGTCATTGG GAACAAGCCG GAAAGCGATA TACTCGTGCA 5461 GACGAGAGCA CCGACGAGAA TGTCATGCTT CTGACTAGCG ACGCCCCTGA 10   5521 TGGGCTCTGG TCATACAGGA TAGCAACGGT GAGAACAAGA TTAAGATGCT 5581 TCTGGAGGAT CTGGTGGTTC TACTAATCTG TCAGATATTA TTGAAAAGGA 5641 CAACTGGTTA TCCAGGAATC CATCCTCATG CTCCCAGAGG AGGTGGAAGA 5701 AACAAGCCGG AAAGCGATAT ACTCGTGCAC ACCGCCTACG ACGAGAGCAC 5761 GTCATGCTTC TGACTAGCGA CGCCCCTGAA TACAAGCCTT GGGCTCTGGT 15   5821 AGCAACGGTG AGAACAAGAT TAAGATGCTC TCTGGTGGTT CTCCCAAGAA 5881 GTCTAACCGG TCATCATCAC CATCACCATT GAGTTTAAAC CCGCTGATCA 5941 TGCCTTCTAG TTGCCAGCCA TCTGTTGTTT GCCCCTCCCC CGTGCCTTCC 6001 AAGGTGCCAC TCCCACTGTC CTTTCCTAAT AAAATGAGGA AATTGCATCG 6061 GTAGGTGTCA TTCTATTCTG GGGGGTGGGG TGGGGCAGGA CAGCAAGGGG 20   6121 AAGACAATAG CAGGCATGCT GGGGATGCGG TGGGCTCTAT GGCTTCTGAG 6181 CCAGCTGGGG CTCGATACCG TCGACCTCTA GCTAGAGCTT GGCGTAATCA 6241 TGTTTCCTGT GTGAAATTGT TATCCGCTCA CAATTCCACA CAACATACGA 6301 TAAAGTGTAA AGCCTAGGGT GCCTAATGAG TGAGCTAACT CACATTAATT 6361 CACTGCCCGC TTTCCAGTCG GGAAACCTGT CGTGCCAGCT GCATTAATGA 25   6421 GCGCGGGGAG AGGCGGTTTG CGTATTGGGC GCTCTTCCGC TTCCTCGCTC 6481 TGCGCTCGGT CGTTCGGCTG CGGCGAGCGG TATCAGCTCA CTCAAAGGCG 6541 TATCCACAGA ATCAGGGGAT AACGCAGGAA AGAACATGTG AGCAAAAGGC 6601 CCAGGAACCG TAAAAAGGCC GCGTTGCTGG CGTTTTTCCA TAGGCTCCGC 6661 AGCATCACAA AAATCGACGC TCAAGTCAGA GGTGGCGAAA CCCGACAGGA 30   6721 ACCAGGCGTT TCCCCCTGGA AGCTCCCTCG TGCGCTCTCC TGTTCCGACC 6781 CCGGATACCT GTCCGCCTTT CTCCCTTCGG GAAGCGTGGC GCTTTCTCAT 6841 GTAGGTATCT CAGTTCGGTG TAGGTCGTTC GCTCCAAGCT GGGCTGTGTG 6901 CCGTTCAGCC CGACCGCTGC GCCTTATCCG GTAACTATCG TCTTGAGTCC 6961 GACACGACTT ATCGCCACTG GCAGCAGCCA CTGGTAACAG GATTAGCAGA 35   7021 TAGGCGGTGC TACAGAGTTC TTGAAGTGGT GGCCTAACTA CGGCTACACT 7081 TATTTGGTAT CTGCGCTCTG CTGAAGCCAG TTACCTTCGG AAAAAGAGTT 7141 GATCCGGCAA ACAAACCACC GCTGGTAGCG GTGGTTTTTT TGTTTGCAAG 7201 CGCGCAGAAA AAAAGGATCT CAAGAAGATC CTTTGATCTT TTCTACGGGG 7261 AGTGGAACGA AAACTCACGT TAAGGGATTT TGGTCATGAG ATTATCAAAA 40   7321 CCTAGATCCT TTTAAATTAA AAATGAAGTT TTAAATCAAT CTAAAGTATA 7381 CTTGGTCTGA CAGTTACCAA TGCTTAATCA GTGAGGCACC TATCTCAGCG CCTAGCTGAT CATACGTGAG AGCCGCATTC GGTGCTAGAC TTTGTCACAG GTCAGATATT GCTCCCAGAG CACCGCCTAC ATACAAGCCT CTCTGGTGGT GACCGGTAAG AGTCATTGGG CGACGAGAAT CATACAGGAT GAAGAGGAAA GCCTCGACTG TTGACCCTGG CATTGTCTGA GAGGATTGGG GCGGAAAGAA TGGTCATAGC GCCGGAAGCA GCGTTGCGCT ATCGGCCAAC ACTGACTCGC GTAATACGGT CAGCAAAAGG CCCCCTGACG CTATAAAGAT CTGCCGCTTA AGCTCACGCT CACGAACCCC AACCCGGTAA GCGAGGTATG AGAAGAACAG GGTAGCTCTT CAGCAGATTA TCTGACGCTC AGGATCTTCA TATGAGTAAA ATCTGTCTAT 2020216484   17 Mar 2026 7441 TTCGTTCATC CATAGTTGCC TGACTCCCCG TCGTGTAGAT AACTACGATA CGGGAGGGCT 7501 TACCATCTGG CCCCAGTGCT GCAATGATAC CGCGAGACCC ACGCTCACCG GCTCCAGATT 7561 TATCAGCAAT AAACCAGCCA GCCGGAAGGG CCGAGCGCAG AAGTGGTCCT GCAACTTTAT 7621 CCGCCTCCAT CCAGTCTATT AATTGTTGCC GGGAAGCTAG AGTAAGTAGT TCGCCAGTTA 5   7681 ATAGTTTGCG CAACGTTGTT GCCATTGCTA CAGGCATCGT GGTGTCACGC TCGTCGTTTG 7741 GTATGGCTTC ATTCAGCTCC GGTTCCCAAC GATCAAGGCG AGTTACATGA TCCCCCATGT 7801 TGTGCAAAAA AGCGGTTAGC TCCTTCGGTC CTCCGATCGT TGTCAGAAGT AAGTTGGCCG 7861 CAGTGTTATC ACTCATGGTT ATGGCAGCAC TGCATAATTC TCTTACTGTC ATGCCATCCG 7921 TAAGATGCTT TTCTGTGACT GGTGAGTACT CAACCAAGTC ATTCTGAGAA TAGTGTATGC 10   7981 GGCGACCGAG TTGCTCTTGC CCGGCGTCAA TACGGGATAA TACCGCGCCA CATAGCAGAA 8041 CTTTAAAAGT GCTCATCATT GGAAAACGTT CTTCGGGGCG AAAACTCTCA AGGATCTTAC 8101 CGCTGTTGAG ATCCAGTTCG ATGTAACCCA CTCGTGCACC CAACTGATCT TCAGCATCTT 8161 TTACTTTCAC CAGCGTTTCT GGGTGAGCAA AAACAGGAAG GCAAAATGCC GCAAAAAAGG 8221 GAATAAGGGC GACACGGAAA TGTTGAATAC TCATACTCTT CCTTTTTCAA TATTATTGAA 15   8281 GCATTTATCA GGGTTATTGT CTCATGAGCG GATACATATT TGAATGTATT TAGAAAAATA 8341 AACAAATAGG GGTTCCGCGC ACATTTCCCC GAAAAGTGCC ACCTGACGTC GACGGATCGG 8401 GAGATCGATC TCCCGATCCC CTAGGGTCGA CTCTCAGTAC AATCTGCTCT GATGCCGCAT 8461 AGTTAAGCCA GTATCTGCTC CCTGCTTGTG TGTTGGAGGT CGCTGAGTAG TGCGCGAGCA 8521 AAATTTAAGC TACAACAAGG CAAGGCTTGA CCGACAATTG CATGAAGAAT CTGCTTAGGG 20   8581 TTAGGCGTTT TGCGCTGCTT CGCGATGTAC GGGCCAGATA TACGCGTTGA CATTGATTAT 8641 TGACTAGTTA TTAATAGTAA TCAATTACGG GGTCATTAGT TCATAGCCCA TATATGGAGT 8701 TCCGCGTTAC ATAACTTACG GTAAATGGCC CGCCTGGCTG ACCGCCCAAC GACCCCCGCC 8761 CATTGACGTC AATAATGACG TATGTTCCCA TAGTAACGCC AATAGGGACT TTCCATTGAC 8821 GTCAATGGGT GGAGTATTTA CGGTAAACTG CCCACTTGGC AGTACATCAA GTGTATC 25          In some embodiments, the cytidine base editor is BE4 having a nucleic acid sequence selected from one of the following: Original BE4 nucleic acid sequence: ATGagctcagagactggcccagtggctgtggaccccacattgagacggcggatcgagccccatgagtt tgaggtattcttcgatccgagagagctccgcaaggagacctgcctgctttacgaaattaattgggggg 30 gccggcactccatttggcgacatacatcacagaacactaacaagcacgtcgaagtcaacttcatcgag aagttcacgacagaaagatatttctgtccgaacacaaggtgcagcattacctggtttctcagctggag ccgcgaatgtagtagggccatcactgaattcctgtcaaggtatccccacgtcactctgtttatttaca tcgcaaggctgtaccaccacgctgacccccgcaatcgacaaggcctgcgggatttgatctcttcaggt gtgactatccaaattatgactgagcaggagtcaggatactgctggagaaactttgtgaattatagccc 35 gagtaatgaagcccactggcctaggtatccccatctgtgggtacgactgtacgttcttgaactgtact gcatcatactgggcctgcctccttgtctcaacattctgagaaggaagcagccacagctgacattcttt accatcgctcttcagtcttgtcattaccagcgactgcccccacacattctctgggccaccgggttgaa atctggtggttcttctggtggttctagcggcagcgagactcccgggacctcagagtccgccacacccg aaagttctggtggttcttctggtggttctgataaaaagtattctattggtttagccatcggcactaat 2020216484   17 Mar 2026 tccgttggatgggctgtcataaccgatgaatacaaagtaccttcaaagaaatttaaggtgttggggaa cacagaccgtcattcgattaaaaagaatcttatcggtgccctcctattcgatagtggcgaaacggcag aggcgactcgcctgaaacgaaccgctcggagaaggtatacacgtcgcaagaaccgaatatgttactta caagaaatttttagcaatgagatggccaaagttgacgattctttctttcaccgtttggaagagtcctt 5 ccttgtcgaagaggacaagaaacatgaacggcaccccatctttggaaacatagtagatgaggtggcat atcatgaaaagtacccaacgatttatcacctcagaaaaaagctagttgactcaactgataaagcggac ctgaggttaatctacttggctcttgcccatatgataaagttccgtgggcactttctcattgagggtga tctaaatccggacaactcggatgtcgacaaactgttcatccagttagtacaaacctataatcagttgt ttgaagagaaccctataaatgcaagtggcgtggatgcgaaggctattcttagcgcccgcctctctaaa 10 tcccgacggctagaaaacctgatcgcacaattacccggagagaagaaaaatgggttgttcggtaacct tatagcgctctcactaggcctgacaccaaattttaagtcgaacttcgacttagctgaagatgccaaat tgcagcttagtaaggacacgtacgatgacgatctcgacaatctactggcacaaattggagatcagtat gcggacttatttttggctgccaaaaaccttagcgatgcaatcctcctatctgacatactgagagttaa tactgagattaccaaggcgccgttatccgcttcaatgatcaaaaggtacgatgaacatcaccaagact 15 tgacacttctcaaggccctagtccgtcagcaactgcctgagaaatataaggaaatattctttgatcag tcgaaaaacgggtacgcaggttatattgacggcggagcgagtcaagaggaattctacaagtttatcaa acccatattagagaagatggatgggacggaagagttgcttgtaaaactcaatcgcgaagatctactgc gaaagcagcggactttcgacaacggtagcattccacatcaaatccacttaggcgaattgcatgctata cttagaaggcaggaggatttttatccgttcctcaaagacaatcgtgaaaagattgagaaaatcctaac 20 ctttcgcataccttactatgtgggacccctggcccgagggaactctcggttcgcatggatgacaagaa agtccgaagaaacgattactccatggaattttgaggaagttgtcgataaaggtgcgtcagctcaatcg ttcatcgagaggatgaccaactttgacaagaatttaccgaacgaaaaagtattgcctaagcacagttt actttacgagtatttcacagtgtacaatgaactcacgaaagttaagtatgtcactgagggcatgcgta aacccgcctttctaagcggagaacagaagaaagcaatagtagatctgttattcaagaccaaccgcaaa 25 gtgacagttaagcaattgaaagaggactactttaagaaaattgaatgcttcgattctgtcgagatctc cggggtagaagatcgatttaatgcgtcacttggtacgtatcatgacctcctaaagataattaaagata aggacttcctggataacgaagagaatgaagatatcttagaagatatagtgttgactcttaccctcttt gaagatcgggaaatgattgaggaaagactaaaaacatacgctcacctgttcgacgataaggttatgaa acagttaaagaggcgtcgctatacgggctggggacgattgtcgcggaaacttatcaacgggataagag 30 acaagcaaagtggtaaaactattctcgattttctaaagagcgacggcttcgccaataggaactttatg cagctgatccatgatgactctttaaccttcaaagaggatatacaaaaggcacaggtttccggacaagg ggactcattgcacgaacatattgcgaatcttgctggttcgccagccatcaaaaagggcatactccaga cagtcaaagtagtggatgagctagttaaggtcatgggacgtcacaaaccggaaaacattgtaatcgag atggcacgcgaaaatcaaacgactcagaaggggcaaaaaaacagtcgagagcggatgaagagaataga 35 agagggtattaaagaactgggcagccagatcttaaaggagcatcctgtggaaaatacccaattgcaga acgagaaactttacctctattacctacaaaatggaagggacatgtatgttgatcaggaactggacata aaccgtttatctgattacgacgtcgatcacattgtaccccaatcctttttgaaggacgattcaatcga 2020216484   17 Mar 2026 caataaagtgcttacacgctcggataagaaccgagggaaaagtgacaatgttccaagcgaggaagtcg taaagaaaatgaagaactattggcggcagctcctaaatgcgaaactgataacgcaaagaaagttcgat aacttaactaaagctgagaggggtggcttgtctgaacttgacaaggccggatttattaaacgtcagct cgtggaaacccgccaaatcacaaagcatgttgcacagatactagattcccgaatgaatacgaaatacg 5 acgagaacgataagctgattcgggaagtcaaagtaatcactttaaagtcaaaattggtgtcggacttc agaaaggattttcaattctataaagttagggagataaataactaccaccatgcgcacgacgcttatct taatgccgtcgtagggaccgcactcattaagaaatacccgaagctagaaagtgagtttgtgtatggtg attacaaagtttatgacgtccgtaagatgatcgcgaaaagcgaacaggagataggcaaggctacagcc aaatacttcttttattctaacattatgaatttctttaagacggaaatcactctggcaaacggagagat 10 acgcaaacgacctttaattgaaaccaatggggagacaggtgaaatcgtatgggataagggccgggact tcgcgacggtgagaaaagttttgtccatgccccaagtcaacatagtaaagaaaactgaggtgcagacc ggagggttttcaaaggaatcgattcttccaaaaaggaatagtgataagctcatcgctcgtaaaaagga ctgggacccgaaaaagtacggtggcttcgatagccctacagttgcctattctgtcctagtagtggcaa aagttgagaagggaaaatccaagaaactgaagtcagtcaaagaattattggggataacgattatggag 15 cgctcgtcttttgaaaagaaccccatcgacttccttgaggcgaaaggttacaaggaagtaaaaaagga tctcataattaaactaccaaagtatagtctgtttgagttagaaaatggccgaaaacggatgttggcta gcgccggagagcttcaaaaggggaacgaactcgcactaccgtctaaatacgtgaatttcctgtattta gcgtcccattacgagaagttgaaaggttcacctgaagataacgaacagaagcaactttttgttgagca gcacaaacattatctcgacgaaatcatagagcaaatttcggaattcagtaagagagtcatcctagctg 20 atgccaatctggacaaagtattaagcgcatacaacaagcacagggataaacccatacgtgagcaggcg gaaaatattatccatttgtttactcttaccaacctcggcgctccagccgcattcaagtattttgacac aacgatagatcgcaaacgatacacttctaccaaggaggtgctagacgcgacactgattcaccaatcca tcacgggattatatgaaactcggatagatttgtcacagcttgggggtgactctggtggttctggagga tctggtggttctactaatctgtcagatattattgaaaaggagaccggtaagcaactggttatccagga 25 atccatcctcatgctcccagaggaggtggaagaagtcattgggaacaagccggaaagcgatatactcg tgcacaccgcctacgacgagagcaccgacgagaatgtcatgcttctgactagcgacgcccctgaatac aagccttgggctctggtcatacaggatagcaacggtgagaacaagattaagatgctctctggtggttc tggaggatctggtggttctactaatctgtcagatattattgaaaaggagaccggtaagcaactggtta tccaggaatccatcctcatgctcccagaggaggtggaagaagtcattgggaacaagccggaaagcgat 30 atactcgtgcacaccgcctacgacgagagcaccgacgagaatgtcatgcttctgactagcgacgcccc tgaatacaagccttgggctctggtcatacaggatagcaacggtgagaacaagattaagatgctctctg gtggttctAAAAGGACGGCGGACGGATCAGAGTTCGAGAGTCCGAAAAAAAAACGAAAGGTCGAAtaa BE4 Codon Optimization 1 nucleic acid sequence: ATGTCATCCGAAACCGGGCCAGTGGCCGTAGACCCAACACTCAGGAGGCGGATAGAACCCCATGAGTT 35 TGAAGTGTTCTTCGACCCCAGAGAGCTGCGCAAAGAGACTTGCCTCCTGTATGAAATAAATTGGGGGG GTCGCCATTCAATTTGGAGGCACACTAGCCAGAATACTAACAAACACGTGGAGGTAAATTTTATCGAG AAGTTTACCACCGAAAGATACTTTTGCCCCAATACACGGTGTTCAATTACCTGGTTTCTGTCATGGAG 2020216484   17 Mar 2026 TCCATGTGGAGAATGTAGTAGAGCGATAACTGAGTTCCTGTCTCGATATCCTCACGTCACGTTGTTTA TATACATCGCTCGGCTTTATCACCATGCGGACCCGCGGAACAGGCAAGGTCTTCGGGACCTCATATCC TCTGGGGTGACCATCCAGATAATGACGGAGCAAGAGAGCGGATACTGCTGGCGAAACTTTGTTAACTA CAGCCCAAGCAATGAGGCACACTGGCCTAGATATCCGCATCTCTGGGTTCGACTGTATGTCCTTGAAC 5 TGTACTGCATAATTCTGGGACTTCCGCCATGCTTGAACATTCTGCGGCGGAAACAACCACAGCTGACC TTTTTCACGATTGCTCTCCAAAGTTGTCACTACCAGCGATTGCCACCCCACATCTTGTGGGCTACTGG ACTCAAGTCTGGAGGAAGTTCAGGCGGAAGCAGCGGGTCTGAAACGCCCGGAACCTCAGAGAGCGCAA CGCCCGAAAGCTCTGGAGGGTCAAGTGGTGGTAGTGATAAGAAATACTCCATCGGCCTCGCCATCGGT ACGAATTCTGTCGGTTGGGCCGTTATCACCGATGAGTACAAGGTCCCTTCTAAGAAATTCAAGGTTTT 10 GGGCAATACAGACCGCCATTCTATAAAAAAAAACCTGATCGGCGCCCTTTTGTTTGACAGTGGTGAGA CTGCTGAAGCGACTCGCCTGAAGCGAACTGCCAGGAGGCGGTATACGAGGCGAAAAAACCGAATTTGT TACCTCCAGGAGATTTTCTCAAATGAAATGGCCAAGGTAGATGATAGTTTTTTTCACCGCTTGGAAGA AAGTTTTCTCGTTGAGGAGGACAAAAAGCACGAGAGGCACCCAATCTTTGGCAACATAGTCGATGAGG TCGCATACCATGAGAAATATCCTACGATCTATCATCTCCGCAAGAAGCTGGTCGATAGCACGGATAAA 15 GCTGACCTCCGGCTGATCTACCTTGCTCTTGCTCACATGATTAAATTCAGGGGCCATTTCCTGATAGA AGGAGACCTCAATCCCGACAATTCTGATGTCGACAAACTGTTTATTCAGCTCGTTCAGACCTATAATC AACTCTTTGAGGAGAACCCCATCAATGCTTCAGGGGTGGACGCAAAGGCCATTTTGTCCGCGCGCTTG AGTAAATCACGACGCCTCGAGAATTTGATAGCTCAACTGCCGGGTGAGAAGAAAAACGGGTTGTTTGG GAATCTCATAGCGTTGAGTTTGGGACTTACGCCAAACTTTAAGTCTAACTTTGATTTGGCCGAAGATG 20 CCAAATTGCAGCTGTCCAAAGATACCTATGATGACGACTTGGATAACCTTCTTGCGCAGATTGGTGAC CAATACGCGGATCTGTTTCTTGCCGCAAAAAATCTGTCCGACGCCATACTCTTGTCCGATATACTGCG CGTCAATACTGAGATAACTAAGGCTCCCCTCAGCGCGTCCATGATTAAAAGATACGATGAGCACCACC AAGATCTCACTCTGTTGAAAGCCCTGGTTCGCCAGCAGCTTCCAGAGAAGTATAAGGAGATATTTTTC GACCAATCTAAAAACGGCTATGCGGGTTACATTGACGGTGGCGCCTCTCAAGAAGAATTCTACAAGTT 25 TATAAAGCCGATACTTGAGAAAATGGACGGTACAGAGGAATTGTTGGTTAAGCTCAATCGCGAGGACT TGTTGAGAAAGCAGCGCACATTTGACAATGGTAGTATTCCACACCAGATTCATCTGGGCGAGTTGCAT GCCATTCTTAGAAGACAAGAAGATTTTTATCCGTTTCTGAAAGATAACAGAGAAAAGATTGAAAAGAT ACTTACCTTTCGCATACCGTATTATGTAGGTCCCCTGGCTAGAGGGAACAGTCGCTTCGCTTGGATGA CTCGAAAATCAGAAGAAACAATAACCCCCTGGAATTTTGAAGAAGTGGTAGATAAAGGTGCGAGTGCC 30 CAATCTTTTATTGAGCGGATGACAAATTTTGACAAGAATCTGCCTAACGAAAAGGTGCTTCCCAAGCA TTCCCTTTTGTATGAATACTTTACAGTATATAATGAACTGACTAAAGTGAAGTACGTTACCGAGGGGA TGCGAAAGCCAGCTTTTCTCAGTGGCGAGCAGAAAAAAGCAATAGTTGACCTGCTGTTCAAGACGAAT AGGAAGGTTACCGTCAAACAGCTCAAAGAAGATTACTTTAAAAAGATCGAATGTTTTGATTCAGTTGA GATAAGCGGAGTAGAGGATAGATTTAACGCAAGTCTTGGAACTTATCATGACCTTTTGAAGATCATCA 35 AGGATAAAGATTTTTTGGACAACGAGGAGAATGAAGATATCCTGGAAGATATAGTACTTACCTTGACG CTTTTTGAAGATCGAGAGATGATCGAGGAGCGACTTAAGACGTACGCACATCTCTTTGACGATAAGGT TATGAAACAATTGAAACGCCGGCGGTATACTGGCTGGGGCAGGCTTTCTCGAAAGCTGATTAATGGTA 2020216484   17 Mar 2026 TCCGCGATAAGCAGTCTGGAAAGACAATCCTTGACTTTCTGAAAAGTGATGGATTTGCAAATAGAAAC TTTATGCAGCTTATACATGATGACTCTTTGACGTTCAAGGAAGACATCCAGAAGGCACAGGTATCCGG CCAAGGGGATAGCCTCCATGAACACATAGCCAACCTGGCCGGCTCACCAGCTATTAAAAAGGGAATAT TGCAAACCGTTAAGGTTGTTGACGAACTCGTTAAGGTTATGGGCCGACACAAACCAGAGAATATCGTG 5 ATTGAGATGGCTAGGGAGAATCAGACCACTCAAAAAGGTCAGAAAAATTCTCGCGAAAGGATGAAGCG AATTGAAGAGGGAATCAAAGAACTTGGCTCTCAAATTTTGAAAGAGCACCCGGTAGAAAACACTCAGC TGCAGAATGAAAAGCTGTATCTGTATTATCTGCAGAATGGTCGAGATATGTACGTTGATCAGGAGCTG GATATCAATAGGCTCAGTGACTACGATGTCGACCACATCGTTCCTCAATCTTTCCTGAAAGATGACTC TATCGACAACAAAGTGTTGACGCGATCAGATAAGAACCGGGGAAAATCCGACAATGTACCCTCAGAAG 10 AAGTTGTCAAGAAGATGAAAAACTATTGGAGACAATTGCTGAACGCCAAGCTCATAACACAACGCAAG TTCGATAACTTGACGAAAGCCGAAAGAGGTGGGTTGTCAGAATTGGACAAAGCTGGCTTTATTAAGCG CCAATTGGTGGAGACCCGGCAGATTACGAAACACGTAGCACAAATTTTGGATTCACGAATGAATACCA AATACGACGAAAACGACAAATTGATACGCGAGGTGAAAGTGATTACGCTTAAGAGTAAGTTGGTTTCC GATTTCAGGAAGGATTTTCAGTTTTACAAAGTAAGAGAAATAAACAACTACCACCACGCCCATGATGC 15 TTACCTCAACGCGGTAGTTGGCACAGCTCTTATCAAAAAATATCCAAAGCTGGAAAGCGAGTTCGTTT ACGGTGACTATAAAGTATACGACGTTCGGAAGATGATAGCCAAATCAGAGCAGGAAATTGGGAAGGCA ACCGCAAAATACTTCTTCTATTCAAACATCATGAACTTCTTTAAGACGGAGATTACGCTCGCGAACGG CGAAATACGCAAGAGGCCCCTCATAGAGACTAACGGCGAAACCGGGGAGATCGTATGGGACAAAGGAC GGGACTTTGCGACCGTTAGAAAAGTACTTTCAATGCCACAAGTGAATATTGTTAAAAAGACAGAAGTA 20 CAAACAGGGGGGTTCAGTAAGGAATCCATTTTGCCCAAGCGGAACAGTGATAAATTGATAGCAAGGAA AAAAGATTGGGACCCTAAGAAGTACGGTGGTTTCGACTCTCCTACCGTTGCATATTCAGTCCTTGTAG TTGCGAAAGTGGAAAAGGGGAAAAGTAAGAAGCTTAAGAGTGTTAAAGAGCTTCTGGGCATAACCATA ATGGAACGGTCTAGCTTCGAGAAAAATCCAATTGACTTTCTCGAGGCTAAAGGTTACAAGGAGGTAAA AAAGGACCTGATAATTAAACTCCCAAAGTACAGTCTCTTCGAGTTGGAGAATGGGAGGAAGAGAATGT 25 TGGCATCTGCAGGGGAGCTCCAAAAGGGGAACGAGCTGGCTCTGCCTTCAAAATACGTGAACTTTCTG TACCTGGCCAGCCACTACGAGAAACTCAAGGGTTCTCCTGAGGATAACGAGCAGAAACAGCTGTTTGT AGAGCAGCACAAGCATTACCTGGACGAGATAATTGAGCAAATTAGTGAGTTCTCAAAAAGAGTAATCC TTGCAGACGCGAATCTGGATAAAGTTCTTTCCGCCTATAATAAGCACCGGGACAAGCCTATACGAGAA CAAGCCGAGAACATCATTCACCTCTTTACCCTTACTAATCTGGGCGCGCCGGCCGCCTTCAAATACTT 30 CGACACCACGATAGACAGGAAAAGGTATACGAGTACCAAAGAAGTACTTGACGCCACTCTCATCCACC AGTCTATAACAGGGTTGTACGAAACGAGGATAGATTTGTCCCAGCTCGGCGGCGACTCAGGAGGGTCA GGCGGCTCCGGTGGATCAACGAATCTTTCCGACATAATCGAGAAAGAAACCGGCAAACAGTTGGTGAT CCAAGAATCAATCCTGATGCTGCCTGAAGAAGTAGAAGAGGTGATTGGCAACAAACCTGAGTCTGACA TTCTTGTCCACACCGCGTATGACGAGAGCACGGACGAGAACGTTATGCTTCTCACTAGCGACGCCCCT 35 GAGTATAAACCATGGGCGCTGGTCATCCAAGATTCCAATGGGGAAAACAAGATTAAGATGCTTAGTGG TGGGTCTGGAGGGAGCGGTGGGTCCACGAACCTCAGCGACATTATTGAAAAAGAGACTGGTAAACAAC TTGTAATACAAGAGTCTATTCTGATGTTGCCTGAAGAGGTGGAGGAGGTGATTGGGAACAAACCGGAG 2020216484   17 Mar 2026 TCTGATATACTTGTTCATACCGCCTATGACGAATCTACTGATGAGAATGTGATGCTTTTaACGTCAGA CGCTCCCGAGTACAAACCCTGGGCTCTGGTGATTCAGGACAGCAATGGTGAGAATAAGATTAAAATGT TGAGTGGGGGCTCAAAGCGCACGGCTGACGGTAGCGAATTTGAGAGCCCCAAAAAAAAACGAAAGGTC GAAtaa 5          BE4 Codon Optimization 2 nucleic acid sequence: ATGAGCAGCGAGACAGGCCCTGTGGCTGTGGATCCTACACTGCGGAGAAGAATCGAGCCCCA CGAGTTCGAGGTGTTCTTCGACCCCAGAGAGCTGCGGAAAGAGACATGCCTGCTGTACGAGATCAACT GGGGCGGCAGACACTCTATCTGGCGGCACACAAGCCAGAACACCAACAAGCACGTGGAAGTGAACTTT ATCGAGAAGTTTACGACCGAGCGGTACTTCTGCCCCAACACCAGATGCAGCATCACCTGGTTTCTGAG 10 CTGGTCCCCTTGCGGCGAGTGCAGCAGAGCCATCACCGAGTTTCTGTCCAGATATCCCCACGTGACCC TGTTCATCTATATCGCCCGGCTGTACCACCACGCCGATCCTAGAAATAGACAGGGACTGCGCGACCTG ATCAGCAGCGGAGTGACCATCCAGATCATGACCGAGCAAGAGAGCGGCTACTGCTGGCGGAACTTCGT GAACTACAGCCCCAGCAACGAAGCCCACTGGCCTAGATATCCTCACCTGTGGGTCCGACTGTACGTGC TGGAACTGTACTGCATCATCCTGGGCCTGCCTCCATGCCTGAACATCCTGAGAAGAAAGCAGCCTCAG 15 CTGACCTTCTTCACAATCGCCCTGCAGAGCTGCCACTACCAGAGACTGCCTCCACACATCCTGTGGGC CACCGGACTTAAGAGCGGAGGATCTAGCGGCGGCTCTAGCGGATCTGAGACACCTGGCACAAGCGAGT CTGCCACACCTGAGAGTAGCGGCGGATCTTCTGGCGGCTCCGACAAGAAGTACTCTATCGGACTGGCC ATCGGCACCAACTCTGTTGGATGGGCCGTGATCACCGACGAGTACAAGGTGCCCAGCAAGAAATTCAA GGTGCTGGGCAACACCGACCGGCACAGCATCAAGAAGAATCTGATCGGCGCCCTGCTGTTCGACTCTG 20 GCGAAACAGCCGAAGCCACCAGACTGAAGAGAACCGCCAGGCGGAGATACACCCGGCGGAAGAACCGG ATCTGCTACCTGCAAGAGATCTTCAGCAACGAGATGGCCAAGGTGGACGACAGCTTCTTCCACAGACT GGAAGAGTCCTTCCTGGTGGAAGAGGACAAGAAGCACGAGCGGCACCCCATCTTCGGCAACATCGTGG ATGAGGTGGCCTACCACGAGAAGTACCCCACCATCTACCACCTGAGAAAGAAACTGGTGGACAGCACC GACAAGGCCGACCTGAGACTGATCTACCTGGCTCTGGCCCACATGATCAAGTTCCGGGGCCACTTTCT 25 GATCGAGGGCGATCTGAACCCCGACAACAGCGACGTGGACAAGCTGTTCATCCAGCTGGTGCAGACCT ACAACCAGCTGTTCGAGGAAAACCCCATCAACGCCTCTGGCGTGGACGCCAAGGCTATCCTGTCTGCC AGACTGAGCAAGAGCAGAAGGCTGGAAAACCTGATCGCCCAGCTGCCTGGCGAGAAGAAGAATGGCCT GTTCGGCAACCTGATTGCCCTGAGCCTGGGACTGACCCCTAACTTCAAGAGCAACTTCGACCTGGCCG AGGATGCCAAACTGCAGCTGAGCAAGGACACCTACGACGACGACCTGGACAATCTGCTGGCCCAGATC 30 GGCGATCAGTACGCCGACTTGTTTCTGGCCGCCAAGAACCTGTCCGACGCCATCCTGCTGAGCGATAT CCTGAGAGTGAACACCGAGATCACAAAGGCCCCTCTGAGCGCCTCTATGATCAAGAGATACGACGAGC ACCACCAGGATCTGACCCTGCTGAAGGCCCTCGTTAGACAGCAGCTGCCAGAGAAGTACAAAGAGATT TTCTTCGATCAGTCCAAGAACGGCTACGCCGGCTACATTGATGGCGGAGCCAGCCAAGAGGAATTCTA CAAGTTCATCAAGCCCATCCTGGAAAAGATGGACGGCACCGAGGAACTGCTGGTCAAGCTGAACAGAG 35 AGGACCTGCTGCGGAAGCAGCGGACCTTCGACAATGGCTCTATCCCTCACCAGATCCACCTGGGAGAG CTGCACGCCATTCTGCGGAGACAAGAGGACTTTTACCCATTCCTGAAGGACAACCGGGAAAAGATCGA GAAGATCCTGACCTTCAGGATCCCCTACTACGTGGGACCACTGGCCAGAGGCAATAGCAGATTCGCCT 2020216484   17 Mar 2026 GGATGACCAGAAAGAGCGAGGAAACCATCACACCCTGGAACTTCGAGGAAGTGGTGGACAAGGGCGCC AGCGCTCAGTCCTTCATCGAGCGGATGACCAACTTCGATAAGAACCTGCCTAACGAGAAGGTGCTGCC CAAGCACTCCCTGCTGTATGAGTACTTCACCGTGTACAACGAGCTGACCAAAGTGAAATACGTGACCG AGGGAATGAGAAAGCCCGCCTTTCTGAGCGGCGAGCAGAAAAAGGCCATTGTGGATCTGCTGTTCAAG 5 ACCAACCGGAAAGTGACCGTGAAGCAGCTGAAAGAGGACTACTTCAAGAAAATCGAGTGCTTCGACAG CGTGGAAATCAGCGGCGTGGAAGATCGGTTCAATGCCAGCCTGGGCACATACCACGACCTGCTGAAAA TTATCAAGGACAAGGACTTCCTGGACAACGAAGAGAACGAGGACATTCTCGAGGACATCGTGCTGACC CTGACACTGTTTGAGGACAGAGAGATGATCGAGGAACGGCTGAAAACATACGCCCACCTGTTCGACGA CAAAGTGATGAAGCAACTGAAGCGGAGGCGGTACACAGGCTGGGGCAGACTGTCTCGGAAGCTGATCA 10 ACGGCATCCGGGATAAGCAGTCCGGCAAGACAATCCTGGATTTCCTGAAGTCCGACGGCTTCGCCAAC AGAAACTTCATGCAGCTGATCCACGACGACAGCCTGACCTTTAAAGAGGACATCCAGAAAGCCCAGGT GTCCGGCCAAGGCGATTCTCTGCACGAGCACATTGCCAACCTGGCCGGATCTCCCGCCATTAAGAAGG GCATCCTGCAGACAGTGAAGGTGGTGGACGAGCTTGTGAAAGTGATGGGCAGACACAAGCCCGAGAAC ATCGTGATCGAAATGGCCAGAGAGAACCAGACCACACAGAAGGGCCAGAAGAACAGCCGCGAGAGAAT 15 GAAGCGGATCGAAGAGGGCATCAAAGAGCTGGGCAGCCAGATCCTGAAAGAACACCCCGTGGAAAACA CCCAGCTGCAGAACGAGAAGCTGTACCTGTACTACCTGCAGAATGGACGGGATATGTACGTGGACCAA GAGCTGGACATCAACCGGCTGAGCGACTACGATGTGGACCATATCGTGCCCCAGAGCTTTCTGAAGGA CGACTCCATCGATAACAAGGTCCTGACCAGAAGCGACAAGAACCGGGGCAAGAGCGATAACGTGCCCT CCGAAGAGGTGGTCAAGAAGATGAAGAACTACTGGCGACAGCTGCTGAACGCCAAGCTGATTACCCAG 20 CGGAAGTTCGATAACCTGACCAAGGCCGAGAGAGGCGGCCTGAGCGAACTTGATAAGGCCGGCTTCAT TAAGCGGCAGCTGGTGGAAACCCGGCAGATCACCAAACACGTGGCACAGATTCTGGACTCCCGGATGA ACACTAAGTACGACGAGAATGACAAGCTGATCCGGGAAGTGAAAGTCATCACCCTGAAGTCTAAGCTG GTGTCCGATTTCCGGAAGGATTTCCAGTTCTACAAAGTGCGGGAAATCAACAACTACCATCACGCCCA CGACGCCTACCTGAATGCCGTTGTTGGAACAGCCCTGATCAAGAAGTATCCCAAGCTGGAAAGCGAGT 25 TCGTGTACGGCGACTACAAGGTGTACGACGTGCGGAAGATGATCGCCAAGAGCGAACAAGAGATCGGC AAGGCTACCGCCAAGTACTTTTTCTACAGCAACATCATGAACTTTTTCAAGACAGAGATCACCCTGGC CAACGGCGAGATCCGGAAAAGACCCCTGATCGAGACAAACGGCGAAACCGGGGAGATCGTGTGGGATA AGGGCAGAGATTTTGCCACAGTGCGGAAAGTGCTGAGCATGCCCCAAGTGAATATCGTGAAGAAAACC GAGGTGCAGACAGGCGGCTTCAGCAAAGAGTCTATCCTGCCTAAGCGGAACAGCGATAAGCTGATCGC 30 CAGAAAGAAGGACTGGGACCCTAAGAAGTACGGCGGCTTCGATAGCCCTACCGTGGCCTATTCTGTGC TGGTGGTGGCCAAAGTGGAAAAGGGCAAGTCCAAAAAGCTCAAGAGCGTGAAAGAGCTGCTGGGGATC ACCATCATGGAAAGAAGCAGCTTTGAGAAGAACCCGATCGACTTTCTGGAAGCCAAGGGCTACAAAGA AGTCAAGAAGGACCTCATCATCAAGCTCCCCAAGTACAGCCTGTTCGAGCTGGAAAATGGCCGGAAGC GGATGCTGGCCTCAGCAGGCGAACTGCAGAAAGGCAATGAACTGGCCCTGCCTAGCAAATACGTCAAC 35 TTCCTGTACCTGGCCAGCCACTATGAGAAGCTGAAGGGCAGCCCCGAGGACAATGAGCAAAAGCAGCT GTTTGTGGAACAGCACAAGCACTACCTGGACGAGATCATCGAGCAGATCAGCGAGTTCTCCAAGAGAG TGATCCTGGCCGACGCTAACCTGGATAAGGTGCTGTCTGCCTATAACAAGCACCGGGACAAGCCTATC 2020216484   17 Mar 2026 AGAGAGCAGGCCGAGAATATCATCCACCTGTTTACCCTGACCAACCTGGGAGCCCCTGCCGCCTTCAA GTACTTCGACACCACCATCGACCGGAAGAGGTACACCAGCACCAAAGAGGTGCTGGACGCCACACTGA TCCACCAGTCTATCACCGGCCTGTACGAAACCCGGATCGACCTGTCTCAGCTCGGCGGCGATTCTGGT GGTTCTGGCGGAAGTGGCGGATCCACCAATCTGAGCGACATCATCGAAAAAGAGACAGGCAAGCAGCT 5 CGTGATCCAAGAATCCATCCTGATGCTGCCTGAAGAGGTTGAGGAAGTGATCGGCAACAAGCCTGAGT CCGACATCCTGGTGCACACCGCCTACGATGAGAGCACCGATGAGAACGTCATGCTGCTGACAAGCGAC GCCCCTGAGTACAAGCCTTGGGCTCTCGTGATTCAGGACAGCAATGGGGAGAACAAGATCAAGATGCT GAGCGGAGGTAGCGGAGGCAGTGGCGGAAGCACAAACCTGTCTGATATCATTGAAAAAGAAACCGGGA AGCAACTGGTCATTCAAGAGTCCATTCTCATGCTCCCGGAAGAAGTCGAGGAAGTCATTGGAAACAAA 10 CCCGAGAGCGATATTCTGGTCCACACAGCCTATGACGAGTCTACAGACGAAAACGTGATGCTCCTGAC CTCTGACGCTCCCGAGTATAAGCCCTGGGCACTTGTTATCCAGGACTCTAACGGGGAAAACAAAATCA AAATGTTGTCCGGCGGCAGCAAGCGGACAGCCGATGGATCTGAGTTCGAGAGCCCCAAGAAGAAACGG AAGGTgGAGtaa By “base editing activity” is meant acting to chemically alter a base within a 15 polynucleotide. In one embodiment, a first base is converted to a second base. In one embodiment, the base editing activity is cytidine deaminase activity, e.g., converting target C•G to T*A. In another embodiment, the base editing activity is adenosine or adenine deaminase activity, e.g., converting A»T to G<". In another embodiment, the base editing activity is cytidine deaminase activity, e.g., converting target C*G to T»A, and adenosine or 20 adenine deaminase activity, e.g., converting A•T to G»C. The term “base editor system” refers to a system for editing a nucleobase of a target nucleotide sequence. In various embodiments, the base editor system comprises (1) a polynucleotide programmable nucleotide binding domain (e.g. Cas9); (2) one or more deaminase domains (e.g. an adenosine deaminase and / or a cytidine deaminase) for 25 deaminating said nucleobase; and (3) one or more guide polynucleotide (e.g., guide RNA). In some embodiments, the base editor (BE) system comprises (1) a polynucleotide programmable nucleotide binding domain (e.g. Cas9), an adenosine deaminase domain and a cytidine deaminase domain for deaminating nucleobases in the target nucleotide sequence; and (2) one or more guide polynucleotides (e.g., guide RNA) in conjunction with the 30 polynucleotide programmable nucleotide binding domain. In some embodiments, the polynucleotide programmable nucleotide binding domain is a polynucleotide programmable DNA binding domain. In some embodiments, the base editor is a cytidine base editor (CBE). In some embodiments, the base editor system is BE4. In some embodiments, the base editor is an adenine or adenosine base editor (ABE). In some embodiments, the base editor is an 2020216484   17 Mar 2026 adenine or adenosine base editor (ABE) and a cytidine base editor (CBE). In some embodiments, the base editor is an abasic editor. In some embodiments, a base editor system may comprise more than one base editing component. For example, a base editor system may include one or more deaminases (e.g., 5 adenosine deaminase, cytidine deaminase). In some embodiments, a single guide polynucleotide may be utilized to target different deaminases to a target nucleic acid sequence. In some embodiments, a single pair of guide polynucleotides may be utilized to target different deaminases to a target nucleic acid sequence. The deaminase domain and the polynucleotide programmable nucleotide binding 10 component of a base editor system may be associated with each other covalently or non-covalently, or any combination of associations and interactions thereof. For example, in some embodiments, one or more deaminase domains can be targeted to a target nucleotide sequence by a polynucleotide programmable nucleotide binding domain. In some embodiments, a polynucleotide programmable nucleotide binding domain can be fused or 15 linked to one or more deaminase domains. In some embodiments, a polynucleotide programmable nucleotide binding domain can target one or more deaminase domains to a target nucleotide sequence by non-covalently interacting with or associating with the deaminase domain. For example, in some embodiments, the deaminase domain can comprise an additional heterologous portion or domain that is capable of interacting with, associating 20 with, or capable of forming a complex with an additional heterologous portion or domain that is part of a polynucleotide programmable nucleotide binding domain. In some embodiments, the additional heterologous portion may be capable of binding to, interacting with, associating with, or forming a complex with a polypeptide. In some embodiments, the additional heterologous portion may be capable of binding to, interacting with, associating 25 with, or forming a complex with a polynucleotide. In some embodiments, the additional heterologous portion may be capable of binding to a guide polynucleotide. In some embodiments, the additional heterologous portion may be capable of binding to a polypeptide linker. In some embodiments, the additional heterologous portion may be capable of binding to a polynucleotide linker. The additional heterologous portion may be a protein domain. In 30 some embodiments, the additional heterologous portion may be a K Homology (KH) domain, a MS2 coat protein domain, a PP7 coat protein domain, a SfMu Com coat protein domain, a steril alpha motif, a telomerase Ku binding motif and Ku protein, a telomerase Sm7 binding motif and Sm7 protein, or a RNA recognition motif. 2020216484   17 Mar 2026 A base editor system may further comprise a guide polynucleotide component. It should be appreciated that components of the base editor system may be associated with each other via covalent bonds, noncovalent interactions, or any combination of associations and interactions thereof. In some embodiments, one or more deaminase domains can be targeted 5 to a target nucleotide sequence by a guide polynucleotide. For example, in some embodiments, the deaminase domain can comprise an additional heterologous portion or domain (e.g., polynucleotide binding domain such as an RNA or DNA binding protein) that is capable of interacting with, associating with, or capable of forming a complex with a portion or segment (e.g., a polynucleotide motif) of a guide polynucleotide. In some 10 embodiments, the additional heterologous portion or domain (e.g., polynucleotide binding domain such as an RNA or DNA binding protein) can be fused or linked to the deaminase domain. In some embodiments, the additional heterologous portion may be capable of binding to, interacting with, associating with, or forming a complex with a polypeptide. In some embodiments, the additional heterologous portion may be capable of binding to, 15 interacting with, associating with, or forming a complex with a polynucleotide. In some embodiments, the additional heterologous portion may be capable of binding to a guide polynucleotide. In some embodiments, the additional heterologous portion may be capable of binding to a polypeptide linker. In some embodiments, the additional heterologous portion may be capable of binding to a polynucleotide linker. The additional heterologous portion 20 may be a protein domain. In some embodiments, the additional heterologous portion may be a K Homology (KH) domain, a MS2 coat protein domain, a PP7 coat protein domain, a SfMu Com coat protein domain, a sterile alpha motif, a telomerase Ku binding motif and Ku protein, a telomerase Sm7 binding motif and Sm7 protein, or a RNA recognition motif. In some embodiments, a base editor system can further comprise an inhibitor of base 25 excision repair (BER) component. It should be appreciated that components of the base editor system may be associated with each other via covalent bonds, noncovalent interactions, or any combination of associations and interactions thereof. The inhibitor of BER component may comprise a BER inhibitor. In some embodiments, the inhibitor of BER can be a uracil DNA glycosylase inhibitor (UGI). In some embodiments, the inhibitor of BER can be an 30 inosine BER inhibitor. In some embodiments, the inhibitor of BER can be targeted to the target nucleotide sequence by the polynucleotide programmable nucleotide binding domain. In some embodiments, a polynucleotide programmable nucleotide binding domain can be fused or linked to an inhibitor of BER. In some embodiments, a polynucleotide 2020216484   17 Mar 2026 programmable nucleotide binding domain can be fused or linked to one or more deaminase domains and an inhibitor of BER. In some embodiments, a polynucleotide programmable nucleotide binding domain can target an inhibitor of BER to a target nucleotide sequence by non-covalently interacting with or associating with the inhibitor of BER. For example, in 5 some embodiments, the inhibitor of BER component can comprise an additional heterologous portion or domain that is capable of interacting with, associating with, or capable of forming a complex with an additional heterologous portion or domain that is part of a polynucleotide programmable nucleotide binding domain. In some embodiments, the inhibitor of BER can be targeted to the target nucleotide 10 sequence by the guide polynucleotide. For example, in some embodiments, the inhibitor of BER can comprise an additional heterologous portion or domain (e.g., polynucleotide binding domain such as an RNA or DNA binding protein) that is capable of interacting with, associating with, or capable of forming a complex with a portion or segment (e.g., a polynucleotide motif) of a guide polynucleotide. In some embodiments, the additional 15   heterologous portion or domain of the guide polynucleotide (e.g., polynucleotide binding domain such as an RNA or DNA binding protein) can be fused or linked to the inhibitor of BER. In some embodiments, the additional heterologous portion may be capable of binding to, interacting with, associating with, or forming a complex with a polynucleotide. In some embodiments, the additional heterologous portion may be capable of binding to a guide 20 polynucleotide. In some embodiments, the additional heterologous portion may be capable of binding to a polypeptide linker. In some embodiments, the additional heterologous portion may be capable of binding to a polynucleotide linker. The additional heterologous portion may be a protein domain. In some embodiments, the additional heterologous portion may be a K Homology (KH) domain, a MS2 coat protein domain, a PP7 coat protein domain, a SfMu 25 Com coat protein domain, a sterile alpha motif, a telomerase Ku binding motif and Ku protein, a telomerase Sm7 binding motif and Sm7 protein, or a RNA recognition motif. The term “Cas9” or “Cas9 domain” refers to an RNA guided nuclease comprising a Cas9 protein, or a fragment thereof (e.g., a protein comprising an active, inactive, or partially active DNA cleavage domain of Cas9, and / or the gRNA binding domain of Cas9). A Cas9 30 nuclease is also referred to sometimes as a Casnl nuclease or a CRISPR (clustered regularly interspaced short palindromic repeat) associated nuclease. CRISPR is an adaptive immune system that provides protection against mobile genetic elements (viruses, transposable elements and conjugative plasmids). CRISPR clusters contain spacers, sequences 2020216484   17 Mar 2026 complementary to antecedent mobile elements, and target invading nucleic acids. CRISPR clusters are transcribed and processed into CRISPR RNA (crRNA). In type II CRISPR systems correct processing of pre-crRNA requires a trans-encoded small RNA (tracrRNA), endogenous ribonuclease 3 (rnc) and a Cas9 protein. The tracrRNA serves as a guide for 5 ribonuclease 3-aided processing of pre-crRNA. Subsequently, Cas9 / crRNA / tracrRNA endonucleolytically cleaves linear or circular dsDNA target complementary to the spacer. The target strand not complementary to crRNA is first cut endonucleolytically, then trimmed 3'-5' exonucleolytically. In nature, DNA-binding and cleavage typically requires protein and both RNAs. However, single guide RNAs (“sgRNA,” or simply “gNRA”) can be engineered 10 so as to incorporate aspects of both the crRNA and tracrRNA into a single RNA species. See, e.g., Jinek M., et al., Science 337:816-821(2012), the entire contents of which is hereby incorporated by reference. Cas9 recognizes a short motif in the CRISPR repeat sequences (the PAM or protospacer adjacent motif) to help distinguish self versus non-self. Cas9 nuclease sequences and structures are well known to those of skill in the art (see, e.g., 15 “Complete genome sequence of an M1 strain of Streptococcus pyogenes.” Ferretti et al., Proc. Natl. Acad. Sci. U.S.A. 98:4658-4663(2001); “CRISPR RNA maturation by transencoded small RNA and host factor RNase III.” Deltcheva E., et al., Nature 471:602-607(2011); and “A programmable dual-RNA-guided DNA endonuclease in adaptive bacterial immunity.” Jinek M., et al., Science 337:816-821(2012), the entire contents of each of which 20 are incorporated herein by reference). Cas9 orthologs have been described in various species, including, but not limited to, S. pyogenes and S. thermophilus. Additional suitable Cas9 nucleases and sequences will be apparent to those of skill in the art based on this disclosure, and such Cas9 nucleases and sequences include Cas9 sequences from the organisms and loci disclosed in Chylinski, Rhun, and Charpentier, “The tracrRNA and Cas9 families of type II 25 CRISPR-Cas immunity systems” (2013) RNA Biology 10:5, 726-737; the entire contents of which are incorporated herein by reference. An exemplary Cas9, is Streptococcus pyogenes Cas9 (spCas9), the amino acid sequence of which is provided below: MDKKYSIGLDIGTNSVGWAVITDDYKVPSKKFKVLGNTDRHSIKKNLIGALLFGSGETAEAT 30 RLKRTARRRYTRRKNRICYLQEIFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFGNIVD EVAYHEKYPTIYHLRKKLADSTDKADLRLIYLALAHMIKFRGHFLIEGDLNPDNSDVDKLFI QLVQIYNQLFEENPINASRVDAKAILSARLSKSRRLENLIAQLPGEKRNGLFGNLIALSLGL TPNFKSNFDLAEDAKLQLSKDTYDDDLDNLLAQIGDQYADLFLAAKNLSDAILLSDILRVNS 2020216484   17 Mar 2026 EITKAPLSASMIKRYDEHHQDLTLLKALVRQQLPEKYKEIFFDQSKNGYAGYIDGGASQEEF YKFIKPILEKMDGTEELLVKLNREDLLRKQRTFDNGSIPHQIHLGELHAILRRQEDFYPFLK DNREKIEKILTFRIPYYVGPLARGNSRFAWMTRKSEETITPWNFEEVVDKGASAQSFIERMT NFDKNLPNEKVLPKHSLLYEYFTVYNELTKVKYVTEGMRKPAFLSGEQKKAIVDLLFKTNRK 5 VTVKQLKEDYFKKIECFDSVEISGVEDRFNASLGAYHDLLKIIKDKDFLDNEENEDILEDIV LTLTLFEDRGMIEERLKTYAHLFDDKVMKQLKRRRYTGWGRLSRKLINGIRDKQSGKTILDF LKSDGFANRNFMQLIHDDSLTFKE DIQKAQVSGQGHSLHEQIANLAGSPAIKKGILQTVKIV DELVKVMGHKPENIVIEMARENQTTQKGQKNSRERMKRIEEGIKELGSQILKEHPVENTQLQ NEKLYLYYLQNGRDMYVDQELDINRLSDYDVDHIVPQSFIKDDSIDNKVLTRSDKNRGKSDN 10 VPSEEVVKKMKNYWRQLLNAKLITQRKFDNLTKAE RGGLSELDKAGFXKRQLVETRQITKHV AQILDSRMNTKYDENDKLIREVKVITLKSKLVSDFRKDFQFYKVREINNYHHAHDAYLNAVV GTALIKKYPKLESEFVYGDYKVYDVRKMIAKSEQEIGKATAKYFFYSNIMNFFKTEITLANG EIRKRPLIETNGETGEIVWDKGRDFATVRKVLSMPQVNIVKKTEVQTGGFSKESIL PKRN S D KLIARKKDWDPKKYGGFDSPTVAYSVLVVAKVEKGKSKKLKSVKELLGITIMERSSFEKNPI 15 DFLEAKGYKEVKKDLIIKLPKYSLFELENGRKRMLASAGELQKGNELALPSKYVNFLYLASH YEKLKGSPEDNEQKQLFVEQHKHYLDEIIEQISEFSKRVILADANLDKVLSAYNKHRDKPIR EQAENIIHLFTLTNLGAPAAFKYFDTTIDRKRYTSTKEVLDATLIHQSITGLYETRIDLSQL GGD (single underline: HNH domain; double underline: RuvC domain) 20          A nuclease-inactivated Cas9 protein may interchangeably be referred to as a “dCas9” protein (for nuclease-“dead” Cas9) or catalytically inactive Cas9. Methods for generating a Cas9 protein (or a fragment thereof) having an inactive DNA cleavage domain are known (See, e.g., Jinek et al., Science. 337:816-821(2012); Qi et al., “Repurposing CRISPR as an RNA-Guided Platform for Sequence-Specific Control of Gene Expression” (2013) Cell. 25   28;152(5):1173-83, the entire contents of each of which are incorporated herein by reference). For example, the DNA cleavage domain of Cas9 is known to include two subdomains, the HNH nuclease subdomain and the RuvC1 subdomain. The HNH subdomain cleaves the strand complementary to the gRNA, whereas the RuvC1 subdomain cleaves the non-complementary strand. Mutations within these subdomains can silence the nuclease 30 activity of Cas9. For example, the mutations D10A and H840A completely inactivate the nuclease activity of S. pyogenes Cas9 (Jinek et al., Science. 337:816-821(2012); Qi et al., Cell. 28;152(5):1173-83 (2013)). In some embodiments, a Cas9 nuclease has an inactive (e.g., an inactivated) DNA cleavage domain, that is, the Cas9 is a nickase, referred to as an “nCas9” protein (for “nickase” Cas9). In some embodiments, proteins comprising fragments 2020216484   17 Mar 2026 of Cas9 are provided. For example, in some embodiments, a protein comprises one of two Cas9 domains: (1) the gRNA binding domain of Cas9; or (2) the DNA cleavage domain of Cas9. In some embodiments, proteins comprising Cas9 or fragments thereof are referred to as “Cas9 variants.” A Cas9 variant shares homology to Cas9, or a fragment thereof. For 5 example, a Cas9 variant is at least about 70% identical, at least about 80% identical, at least about 90% identical, at least about 95% identical, at least about 96% identical, at least about 97% identical, at least about 98% identical, at least about 99% identical, at least about 99.5% identical, or at least about 99.9% identical to wild-type Cas9. In some embodiments, the Cas9 variant may have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 10   22, 21, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 or more amino acid changes compared to wild-type Cas9. In some embodiments, the Cas9 variant comprises a fragment of Cas9 (e.g., a gRNA binding domain or a DNA-cleavage domain), such that the fragment is at least about 70% identical, at least about 80% identical, at least about 90% identical, at least about 95% identical, at least about 15   96% identical, at least about 97% identical, at least about 98% identical, at least about 99% identical, at least about 99.5% identical, or at least about 99.9% identical to the corresponding fragment of wild-type Cas9. In some embodiments, the fragment is at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95% identical, at least 20   96%, at least 97%, at least 98%, at least 99%, or at least 99.5% of the amino acid length of a corresponding wild-type Cas9. In some embodiments, the fragment is at least 100 amino acids in length. In some embodiments, the fragment is at least 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, or at least 1300 25 amino acids in length. In some embodiments, wild-type Cas9 corresponds to Cas9 from Streptococcus pyogenes (NCBI Reference Sequence: NC_017053.1, nucleotide and amino acid sequences as follows). ATGGATAAGAAATACTCAATAGGCTTAGATATCGGCACAAATAGCGTCGGATGGGCGGTGAT 30 CACTGATGATTATAAGGTTCCGTCTAAAAAGTTCAAGGTTCTGGGAAATACAGACCGCCACA GTATCAAAAAAAATCTTATAGGGGCTCTTTTATTTGGCAGTGGAGAGACAGCGGAAGCGACT CGTCTCAAACGGACAGCTCGTAGAAGGTATACACGTCGGAAGAATCGTATTTGTTATCTACA GGAGATTTTTTCAAATGAGATGGCGAAAGTAGATGATAGTTTCTTTCATCGACTTGAAGAGT 2020216484   17 Mar 2026 CTTTTTTGGTGGAAGAAGACAAGAAGCATGAACGTCATCCTATTTTTGGAAATATAGTAGAT GAAGTTGCTTATCATGAGAAATATCCAACTATCTATCATCTGCGAAAAAAATTGGCAGATTC TACTGATAAAGCGGATTTGCGCTTAATCTATTTGGCCTTAGCGCATATGATTAAGTTTCGTG GTCATTTTTTGATTGAGGGAGATTTAAATCCTGATAATAGTGATGTGGACAAACTATTTATC 5 CAGTTGGTACAAATCTACAATCAATTATTTGAAGAAAACCCTATTAACGCAAGTAGAGTAGA TGCTAAAGCGATTCTTTCTGCACGATTGAGTAAATCAAGACGATTAGAAAATCTCATTGCTC AGCTCCCCGGTGAGAAGAGAAATGGCTTGTTTGGGAATCTCATTGCTTTGTCATTGGGATTG ACCCCTAATTTTAAATCAAATTTTGATTTGGCAGAAGATGCTAAATTACAGCTTTCAAAAGA TACTTACGATGATGATTTAGATAATTTATTGGCGCAAATTGGAGATCAATATGCTGATTTGT 10 TTTTGGCAGCTAAGAATTTATCAGATGCTATTTTACTTTCAGATATCCTAAGAGTAAATAGT GAAATAACTAAGGCTCCCCTATCAGCTTCAATGATTAAGCGCTACGATGAACATCATCAAGA CTTGACTCTTTTAAAAGCTTTAGTTCGACAACAACTTCCAGAAAAGTATAAAGAAATCTTTT TTGATCAATCAAAAAACGGATATGCAGGTTATATTGATGGGGGAGCTAGCCAAGAAGAATTT TATAAATTTATCAAACCAATTTTAGAAAAAATGGATGGTACTGAGGAATTATTGGTGAAACT 15 AAATCGTGAAGATTTGCTGCGCAAGCAACGGACCTTTGACAACGGCTCTATTCCCCATCAAA TTCACTTGGGTGAGCTGCATGCTATTTTGAGAAGACAAGAAGACTTTTATCCATTTTTAAAA GACAATCGTGAGAAGATTGAAAAAATCTTGACTTTTCGAATTCCTTATTATGTTGGTCCATT GGCGCGTGGCAATAGTCGTTTTGCATGGATGACTCGGAAGTCTGAAGAAACAATTACCCCAT GGAATTTTGAAGAAGTTGTCGATAAAGGTGCTTCAGCTCAATCATTTATTGAACGCATGACA 20 AACTTTGATAAAAATCTTCCAAATGAAAAAGTACTACCAAAACATAGTTTGCTTTATGAGTA TTTTACGGTTTATAACGAATTGACAAAGGTCAAATATGTTACTGAGGGAATGCGAAAACCAG CATTTCTTTCAGGTGAACAGAAGAAAGCCATTGTTGATTTACTCTTCAAAACAAATCGAAAA GTAACCGTTAAGCAATTAAAAGAAGATTATTTCAAAAAAATAGAATGTTTTGATAGTGTTGA AATTTCAGGAGTTGAAGATAGATTTAATGCTTCATTAGGCGCCTACCATGATTTGCTAAAAA 25 TTATTAAAGATAAAGATTTTTTGGATAATGAAGAAAATGAAGATATCTTAGAGGATATTGTT TTAACATTGACCTTATTTGAAGATAGGGGGATGATTGAGGAAAGACTTAAAACATATGCTCA CCTCTTTGATGATAAGGTGATGAAACAGCTTAAACGTCGCCGTTATACTGGTTGGGGACGTT TGTCTCGAAAATTGATTAATGGTATTAGGGATAAGCAATCTGGCAAAACAATATTAGATTTT TTGAAATCAGATGGTTTTGCCAATCGCAATTTTATGCAGCTGATCCATGATGATAGTTTGAC 30 ATTTAAAGAAGATATTCAAAAAGCACAGGTGTCTGGACAAGGCCATAGTTTACATGAACAGA TTGCTAACTTAGCTGGCAGTCCTGCTATTAAAAAAGGTATTTTACAGACTGTAAAAATTGTT GATGAACTGGTCAAAGTAATGGGGCATAAGCCAGAAAATATCGTTATTGAAATGGCACGTGA AAATCAGACAACTCAAAAGGGCCAGAAAAATTCGCGAGAGCGTATGAAACGAATCGAAGAAG GTATCAAAGAATTAGGAAGTCAGATTCTTAAAGAGCATCCTGTTGAAAATACTCAATTGCAA 2020216484   17 Mar 2026 AATGAAAAGCTCTATCTCTATTATCTACAAAATGGAAGAGACATGTATGTGGACCAAGAATT AGATATTAATCGTTTAAGTGATTATGATGTCGATCACATTGTTCCACAAAGTTTCATTAAAG ACGATTCAATAGACAATAAGGTACTAACGCGTTCTGATAAAAATCGTGGTAAATCGGATAAC GTTCCAAGTGAAGAAGTAGTCAAAAAGATGAAAAACTATTGGAGACAACTTCTAAACGCCAA 5 GTTAATCACTCAACGTAAGTTTGATAATTTAACGAAAGCTGAACGTGGAGGTTTGAGTGAAC TTGATAAAGCTGGTTTTATCAAACGCCAATTGGTTGAAACTCGCCAAATCACTAAGCATGTG GCACAAATTTTGGATAGTCGCATGAATACTAAATACGATGAAAATGATAAACTTATTCGAGA GGTTAAAGTGATTACCTTAAAATCTAAATTAGTTTCTGACTTCCGAAAAGATTTCCAATTCT ATAAAGTACGTGAGATTAACAATTACCATCATGCCCATGATGCGTATCTAAATGCCGTCGTT 10 GGAACTGCTTTGATTAAGAAATATCCAAAACTTGAATCGGAGTTTGTCTATGGTGATTATAA AGTTTATGATGTTCGTAAAATGATTGCTAAGTCTGAGCAAGAAATAGGCAAAGCAACCGCAA AATATTTCTTTTACTCTAATATCATGAACTTCTTCAAAACAGAAATTACACTTGCAAATGGA GAGATTCGCAAACGCCCTCTAATCGAAACTAATGGGGAAACTGGAGAAATTGTCTGGGATAA AGGGCGAGATTTTGCCACAGTGCGCAAAGTATTGTCCATGCCCCAAGTCAATATTGTCAAGA 15 AAACAGAAGTACAGACAGGCGGATTCTCCAAGGAGTCAATTTTACCAAAAAGAAATTCGGAC AAGCTTATTGCTCGTAAAAAAGACTGGGATCCAAAAAAATATGGTGGTTTTGATAGTCCAAC GGTAGCTTATTCAGTCCTAGTGGTTGCTAAGGTGGAAAAAGGGAAATCGAAGAAGTTAAAAT CCGTTAAAGAGTTACTAGGGATCACAATTATGGAAAGAAGTTCCTTTGAAAAAAATCCGATT GACTTTTTAGAAGCTAAAGGATATAAGGAAGTTAAAAAAGACTTAATCATTAAACTACCTAA 20 ATATAGTCTTTTTGAGTTAGAAAACGGTCGTAAACGGATGCTGGCTAGTGCCGGAGAATTAC AAAAAGGAAATGAGCTGGCTCTGCCAAGCAAATATGTGAATTTTTTATATTTAGCTAGTCAT TATGAAAAGTTGAAGGGTAGTCCAGAAGATAACGAACAAAAACAATTGTTTGTGGAGCAGCA TAAGCATTATTTAGATGAGATTATTGAGCAAATCAGTGAATTTTCTAAGCGTGTTATTTTAG CAGATGCCAATTTAGATAAAGTTCTTAGTGCATATAACAAACATAGAGACAAACCAATACGT 25 GAACAAGCAGAAAATATTATTCATTTATTTACGTTGACGAATCTTGGAGCTCCCGCTGCTTT TAAATATTTTGATACAACAATTGATCGTAAACGATATACGTCTACAAAAGAAGTTTTAGATG CCACTCTTATCCATCAATCCATCACTGGTCTTTATGAAACACGCATTGATTTGAGTCAGCTA GGAGGTGACTGA 30 MDKKYSIGLDIGTNSVGWAVITDDYKVPSKKFKVLGNTDRHSIKKNLIGALLFGSGETAEAT RLKRTARRRYTRRKNRICYLQEIFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFGNIVD EVAYHEKYPTIYHLRKKLADSTDKADLRLIYLALAHMIKFRGHFLIEGDLNPDNSDVDKLFI QLVQIYNQLFEENPINASRVDAKAILSARLSKSRRLENLIAQLPGEKRNGLFGNLIALSLGL TPNFKSNFDLAEDAKLQLSKDTYDDDLDNLLAQIGDQYADLFLAAKNLSDAILLSDILRVNS 2020216484   17 Mar 2026 EITKAPLSASMIKRYDEHHQDLTLLKALVRQQLPEKYKEIFFDQSKNGYAGYIDGGASQEEF YKFIKPILEKMDGTEELLVKLNREDLLRKQRTFDNGSIPHQIHLGELHAILRRQEDFYPFLK DNREKIEKILTFRIPYYVGPLARGNSRFAWMTRKSEETITPWNFEEVVDKGASAQSFIERMT NFDKNLPNEKVLPKHSLLYEYFTVYNELTKVKYVTEGMRKPAFLSGEQKKAIVDLLFKTNRK 5 VTVKQLKEDYFKKIECFDSVEISGVEDRFNASLGAYHDLLKIIKDKDFLDNEENEDILEDIV LTLTLFEDRGMIEERLKTYAHLFDDKVMKQLKRRRYTGWGRLSRKLINGIRDKQSGKTILDF LKSDGFANRNFMQLIHDDSLTFKE DIQKAQVSGQGHSLHEQIANLAGSPAIKKGILQTVKIV DELVKVMGHKPENIVIEMARENQTTQKGQKNSRERMKRIEEGIKELGSQILKEHPVENTQLQ NEKLYLYYLQNGRDMYVDQELDINRLSDYDVDHIVPQSFIKDDSIDNKVLTRSDKNRGKSDN 10 VPSEEVVKKMKNYWRQLLNAKLITQRKFDNLTKAE RGGLSELDKAGFXKRQLVETRQITKHV AQILDSRMNTKYDENDKLIREVKVITLKSKLVSDFRKDFQFYKVREINNYHHAHDAYLNAVV GTALIKKYPKLESEFVYGDYKVYDVRKMIAKSEQEIGKATAKYFFYSNIMNFFKTEITLANG EIRKRPLIETNGETGEIVWDKGRDFATVRKVLSMPQVNIVKKTEVQTGGFSKESIL PKRN S D KLIARKKDWDPKKYGGFDSPTVAYSVLVVAKVEKGKSKKLKSVKELLGITIMERSSFEKNPI 15 DFLEAKGYKEVKKDLIIKLPKYSLFELENGRKRMLASAGELQKGNELALPSKYVNFLYLASH YEKLKGSPEDNEQKQLFVEQHKHYLDEIIEQISEFSKRVILADANLDKVLSAYNKHRDKPIR EQAENIIHLFTLTNLGAPAAFKYFDTTIDRKRYTSTKEVLDATLIHQSITGLYETRIDLSQL GGD (single underline: HNH domain; double underline: RuvC domain) 20          In some embodiments, wild-type Cas9 corresponds to, or comprises the following nucleotide and / or amino acid sequences: ATGGATAAAAAGTATTCTATTGGTTTAGACATCGGCACTAATTCCGTTGGATGGGCTGTCAT AACCGATGAATACAAAGTACCTTCAAAGAAATTTAAGGTGTTGGGGAACACAGACCGTCATT CGATTAAAAAGAATCTTATCGGTGCCCTCCTATTCGATAGTGGCGAAACGGCAGAGGCGACT 25 CGCCTGAAACGAACCGCTCGGAGAAGGTATACACGTCGCAAGAACCGAATATGTTACTTACA AGAAATTTTTAGCAATGAGATGGCCAAAGTTGACGATTCTTTCTTTCACCGTTTGGAAGAGT CCTTCCTTGTCGAAGAGGACAAGAAACATGAACGGCACCCCATCTTTGGAAACATAGTAGAT GAGGTGGCATATCATGAAAAGTACCCAACGATTTATCACCTCAGAAAAAAGCTAGTTGACTC AACTGATAAAGCGGACCTGAGGTTAATCTACTTGGCTCTTGCCCATATGATAAAGTTCCGTG 30 GGCACTTTCTCATTGAGGGTGATCTAAATCCGGACAACTCGGATGTCGACAAACTGTTCATC CAGTTAGTACAAACCTATAATCAGTTGTTTGAAGAGAACCCTATAAATGCAAGTGGCGTGGA TGCGAAGGCTATTCTTAGCGCCCGCCTCTCTAAATCCCGACGGCTAGAAAACCTGATCGCAC AATTACCCGGAGAGAAGAAAAATGGGTTGTTCGGTAACCTTATAGCGCTCTCACTAGGCCTG ACACCAAATTTTAAGTCGAACTTCGACTTAGCTGAAGATGCCAAATTGCAGCTTAGTAAGGA 2020216484   17 Mar 2026 CACGTACGATGACGATCTCGACAATCTACTGGCACAAATTGGAGATCAGTATGCGGACTTAT TTTTGGCTGCCAAAAACCTTAGCGATGCAATCCTCCTATCTGACATACTGAGAGTTAATACT GAGATTACCAAGGCGCCGTTATCCGCTTCAATGATCAAAAGGTACGATGAACATCACCAAGA CTTGACACTTCTCAAGGCCCTAGTCCGTCAGCAACTGCCTGAGAAATATAAGGAAATATTCT 5 TTGATCAGTCGAAAAACGGGTACGCAGGTTATATTGACGGCGGAGCGAGTCAAGAGGAATTC TACAAGTTTATCAAACCCATATTAGAGAAGATGGATGGGACGGAAGAGTTGCTTGTAAAACT CAATCGCGAAGATCTACTGCGAAAGCAGCGGACTTTCGACAACGGTAGCATTCCACATCAAA TCCACTTAGGCGAATTGCATGCTATACTTAGAAGGCAGGAGGATTTTTATCCGTTCCTCAAA GACAATCGTGAAAAGATTGAGAAAATCCTAACCTTTCGCATACCTTACTATGTGGGACCCCT 10 GGCCCGAGGGAACTCTCGGTTCGCATGGATGACAAGAAAGTCCGAAGAAACGATTACTCCAT GGAATTTTGAGGAAGTTGTCGATAAAGGTGCGTCAGCTCAATCGTTCATCGAGAGGATGACC AACTTTGACAAGAATTTACCGAACGAAAAAGTATTGCCTAAGCACAGTTTACTTTACGAGTA TTTCACAGTGTACAATGAACTCACGAAAGTTAAGTATGTCACTGAGGGCATGCGTAAACCCG CCTTTCTAAGCGGAGAACAGAAGAAAGCAATAGTAGATCTGTTATTCAAGACCAACCGCAAA 15 GTGACAGTTAAGCAATTGAAAGAGGACTACTTTAAGAAAATTGAATGCTTCGATTCTGTCGA GATCTCCGGGGTAGAAGATCGATTTAATGCGTCACTTGGTACGTATCATGACCTCCTAAAGA TAATTAAAGATAAGGACTTCCTGGATAACGAAGAGAATGAAGATATCTTAGAAGATATAGTG TTGACTCTTACCCTCTTTGAAGATCGGGAAATGATTGAGGAAAGACTAAAAACATACGCTCA CCTGTTCGACGATAAGGTTATGAAACAGTTAAAGAGGCGTCGCTATACGGGCTGGGGACGAT 20 TGTCGCGGAAACTTATCAACGGGATAAGAGACAAGCAAAGTGGTAAAACTATTCTCGATTTT CTAAAGAGCGACGGCTTCGCCAATAGGAACTTTATGCAGCTGATCCATGATGACTCTTTAAC CTTCAAAGAGGATATACAAAAGGCACAGGTTTCCGGACAAGGGGACTCATTGCACGAACATA TTGCGAATCTTGCTGGTTCGCCAGCCATCAAAAAGGGCATACTCCAGACAGTCAAAGTAGTG GATGAGCTAGTTAAGGTCATGGGACGTCACAAACCGGAAAACATTGTAATCGAGATGGCACG 25 CGAAAATCAAACGACTCAGAAGGGGCAAAAAAACAGTCGAGAGCGGATGAAGAGAATAGAAG AGGGTATTAAAGAACTGGGCAGCCAGATCTTAAAGGAGCATCCTGTGGAAAATACCCAATTG CAGAACGAGAAACTTTACCTCTATTACCTACAAAATGGAAGGGACATGTATGTTGATCAGGA ACTGGACATAAACCGTTTATCTGATTACGACGTCGATCACATTGTACCCCAATCCTTTTTGA AGGACGATTCAATCGACAATAAAGTGCTTACACGCTCGGATAAGAACCGAGGGAAAAGTGAC 30 AATGTTCCAAGCGAGGAAGTCGTAAAGAAAATGAAGAACTATTGGCGGCAGCTCCTAAATGC GAAACTGATAACGCAAAGAAAGTTCGATAACTTAACTAAAGCTGAGAGGGGTGGCTTGTCTG AACTTGACAAGGCCGGATTTATTAAACGTCAGCTCGTGGAAACCCGCCAAATCACAAAGCAT GTTGCACAGATACTAGATTCCCGAATGAATACGAAATACGACGAGAACGATAAGCTGATTCG GGAAGTCAAAGTAATCACTTTAAAGTCAAAATTGGTGTCGGACTTCAGAAAGGATTTTCAAT 2020216484   17 Mar 2026 TCTATAAAGTTAGGGAGATAAATAACTACCACCATGCGCACGACGCTTATCTTAATGCCGTC GTAGGGACCGCACTCATTAAGAAATACCCGAAGCTAGAAAGTGAGTTTGTGTATGGTGATTA CAAAGTTTATGACGTCCGTAAGATGATCGCGAAAAGCGAACAGGAGATAGGCAAGGCTACAG CCAAATACTTCTTTTATTCTAACATTATGAATTTCTTTAAGACGGAAATCACTCTGGCAAAC 5 GGAGAGATACGCAAACGACCTTTAATTGAAACCAATGGGGAGACAGGTGAAATCGTATGGGA TAAGGGCCGGGACTTCGCGACGGTGAGAAAAGTTTTGTCCATGCCCCAAGTCAACATAGTAA AGAAAACTGAGGTGCAGACCGGAGGGTTTTCAAAGGAATCGATTCTTCCAAAAAGGAATAGT GATAAGCTCATCGCTCGTAAAAAGGACTGGGACCCGAAAAAGTACGGTGGCTTCGATAGCCC TACAGTTGCCTATTCTGTCCTAGTAGTGGCAAAAGTTGAGAAGGGAAAATCCAAGAAACTGA 10 AGTCAGTCAAAGAATTATTGGGGATAACGATTATGGAGCGCTCGTCTTTTGAAAAGAACCCC ATCGACTTCCTTGAGGCGAAAGGTTACAAGGAAGTAAAAAAGGATCTCATAATTAAACTACC AAAGTATAGTCTGTTTGAGTTAGAAAATGGCCGAAAACGGATGTTGGCTAGCGCCGGAGAGC TTCAAAAGGGGAACGAACTCGCACTACCGTCTAAATACGTGAATTTCCTGTATTTAGCGTCC CATTACGAGAAGTTGAAAGGTTCACCTGAAGATAACGAACAGAAGCAACTTTTTGTTGAGCA 15 GCACAAACATTATCTCGACGAAATCATAGAGCAAATTTCGGAATTCAGTAAGAGAGTCATCC TAGCTGATGCCAATCTGGACAAAGTATTAAGCGCATACAACAAGCACAGGGATAAACCCATA CGTGAGCAGGCGGAAAATATTATCCATTTGTTTACTCTTACCAACCTCGGCGCTCCAGCCGC ATTCAAGTATTTTGACACAACGATAGATCGCAAACGATACACTTCTACCAAGGAGGTGCTAG ACGCGACACTGATTCACCAATCCATCACGGGATTATATGAAACTCGGATAGATTTGTCACAG 20 CTTGGGGGTGACGGATCCCCCAAGAAGAAGAGGAAAGTCTCGAGCGACTACAAAGACCATGA CGGTGATTATAAAGATCATGACATCGATTACAAGGATGACGATGACAAGGCTGCAGGA MDKKYSIGLAIGTNSVGWAVITDEYKVPSKKFKVLGNTDRHSIKKNLIGALLFDSGETAEAT RLKRTARRRYTRRKNRICYLQEIFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFGNIVD 25 EVAYHEKYPTIYHLRKKLVDSTDKADLRLIYLALAHMIKFRGHFLIEGDLNPDNSDVDKLFI QLVQTYNQLFEENPINASGVDAKAILSARLSKSRRLENLIAQLPGEKKNGLFGNLIALSLGL TPNFKSNFDLAEDAKLQLSKDTYDDDLDNLLAQIGDQYADLFLAAKNLSDAILLSDILRVNT EITKAPLSASMIKRYDEHHQDLTLLKALVRQQLPEKYKEIFFDQSKNGYAGYIDGGASQEEF YKFIKPILEKMDGTEELLVKLNREDLLRKQRTFDNGSIPHQIHLGELHAILRRQEDFYPFLK 30 DNREKIEKILTFRIPYYVGPLARGNSRFAWMTRKSEETITPWNFEEVVDKGASAQSFIERMT NFDKNLPNEKVLPKHSLLYEYFTVYNELTKVKYVTEGMRKPAFLSGEQKKAIVDLLFKTNRK VTVKQLKEDYFKKIECFDSVEISGVEDRFNASLGTYHDLLKIIKDKDFLDNEENEDILEDIV LTLTLFEDREMIEERLKTYAHLFDDKVMKQLKRRRYTGWGRLSRKLINGIRDKQSGKTILDF LKSDGFANRNFMQLIHDDSLTFKE DIQKAQVSGQGDSLHEHIANLAGSPAIKKGILQTVKVV 2020216484   17 Mar 2026 DELVKVMGRHKPENIVIEMARENQTTQKGQKNSRERMKRIEEGIKELGSQILKEHPVENTQL QNEKLYLYYLQNGRDMYVDQELDINRLSDYDVDHIVPQSFLKDDSIDNKVLTRSDKNRGKSD NVPSEEVVKKMKNYWRQLLNAKLITQRKFDNLTKAERGGLSELDKAGFIKRQLVETRQITKH VAQILDSRMNTKYDENDKLIREVKVITLKSKLVSDFRKDFQFYKVREINNYHHAHDAyLNAV 5 VGTALIKKYPKLESEFVYGDYKVYDVRKMIAKSEQEIGKATAKYFFYSNIMNFFKTEITLAN GEIRKRPLIETNGETGEIVWDKGRDFATVRKVLSMPQVNIVKKTEVQTGGFSKE SIL PKRNS DKLIARKKDWDPKKYGGFDSPTVAYSVLVVAKVEKGKSKKLKSVKELLGITIMERSSFEKNP IDFLEAKGYKEVKKDLIIKLPKYSLFELENGRKRMLASAGELQKGNELALPSKYVNFLYLAS HYEKLKGSPEDNEQKQLFVEQHKHYLDEIIEQISEFSKRVILADANLDKVLSAYNKHRDKPI 10 REQAENIIHLFTLTNLGAPAAFKYFDTTIDRKRYTSTKEVLDATLIHQSITGLYETRIDLSQ LGGD (single underline: HNH domain; double underline: RuvC domain) In some embodiments, wild-type Cas9 corresponds to Cas9 from Streptococcus pyogenes (NCBI Reference Sequence: NC_002737.2 (nucleotide sequence as follows); and 15 Uniprot Reference Sequence: Q99ZW2 (amino acid sequence as follows). ATGGATAAGAAATACTCAATAGGCTTAGATATCGGCACAAATAGCGTCGGATGGGCGGTGAT CACTGATGAATATAAGGTTCCGTCTAAAAAGTTCAAGGTTCTGGGAAATACAGACCGCCACA GTATCAAAAAAAATCTTATAGGGGCTCTTTTATTTGACAGTGGAGAGACAGCGGAAGCGACT CGTCTCAAACGGACAGCTCGTAGAAGGTATACACGTCGGAAGAATCGTATTTGTTATCTACA 20 GGAGATTTTTTCAAATGAGATGGCGAAAGTAGATGATAGTTTCTTTCATCGACTTGAAGAGT CTTTTTTGGTGGAAGAAGACAAGAAGCATGAACGTCATCCTATTTTTGGAAATATAGTAGAT GAAGTTGCTTATCATGAGAAATATCCAACTATCTATCATCTGCGAAAAAAATTGGTAGATTC TACTGATAAAGCGGATTTGCGCTTAATCTATTTGGCCTTAGCGCATATGATTAAGTTTCGTG GTCATTTTTTGATTGAGGGAGATTTAAATCCTGATAATAGTGATGTGGACAAACTATTTATC 25 CAGTTGGTACAAACCTACAATCAATTATTTGAAGAAAACCCTATTAACGCAAGTGGAGTAGA TGCTAAAGCGATTCTTTCTGCACGATTGAGTAAATCAAGACGATTAGAAAATCTCATTGCTC AGCTCCCCGGTGAGAAGAAAAATGGCTTATTTGGGAATCTCATTGCTTTGTCATTGGGTTTG ACCCCTAATTTTAAATCAAATTTTGATTTGGCAGAAGATGCTAAATTACAGCTTTCAAAAGA TACTTACGATGATGATTTAGATAATTTATTGGCGCAAATTGGAGATCAATATGCTGATTTGT 30 TTTTGGCAGCTAAGAATTTATCAGATGCTATTTTACTTTCAGATATCCTAAGAGTAAATACT GAAATAACTAAGGCTCCCCTATCAGCTTCAATGATTAAACGCTACGATGAACATCATCAAGA CTTGACTCTTTTAAAAGCTTTAGTTCGACAACAACTTCCAGAAAAGTATAAAGAAATCTTTT TTGATCAATCAAAAAACGGATATGCAGGTTATATTGATGGGGGAGCTAGCCAAGAAGAATTT TATAAATTTATCAAACCAATTTTAGAAAAAATGGATGGTACTGAGGAATTATTGGTGAAACT 2020216484   17 Mar 2026 AAATCGTGAAGATTTGCTGCGCAAGCAACGGACCTTTGACAACGGCTCTATTCCCCATCAAA TTCACTTGGGTGAGCTGCATGCTATTTTGAGAAGACAAGAAGACTTTTATCCATTTTTAAAA GACAATCGTGAGAAGATTGAAAAAATCTTGACTTTTCGAATTCCTTATTATGTTGGTCCATT GGCGCGTGGCAATAGTCGTTTTGCATGGATGACTCGGAAGTCTGAAGAAACAATTACCCCAT 5 GGAATTTTGAAGAAGTTGTCGATAAAGGTGCTTCAGCTCAATCATTTATTGAACGCATGACA AACTTTGATAAAAATCTTCCAAATGAAAAAGTACTACCAAAACATAGTTTGCTTTATGAGTA TTTTACGGTTTATAACGAATTGACAAAGGTCAAATATGTTACTGAAGGAATGCGAAAACCAG CATTTCTTTCAGGTGAACAGAAGAAAGCCATTGTTGATTTACTCTTCAAAACAAATCGAAAA GTAACCGTTAAGCAATTAAAAGAAGATTATTTCAAAAAAATAGAATGTTTTGATAGTGTTGA 10 AATTTCAGGAGTTGAAGATAGATTTAATGCTTCATTAGGTACCTACCATGATTTGCTAAAAA TTATTAAAGATAAAGATTTTTTGGATAATGAAGAAAATGAAGATATCTTAGAGGATATTGTT TTAACATTGACCTTATTTGAAGATAGGGAGATGATTGAGGAAAGACTTAAAACATATGCTCA CCTCTTTGATGATAAGGTGATGAAACAGCTTAAACGTCGCCGTTATACTGGTTGGGGACGTT TGTCTCGAAAATTGATTAATGGTATTAGGGATAAGCAATCTGGCAAAACAATATTAGATTTT 15 TTGAAATCAGATGGTTTTGCCAATCGCAATTTTATGCAGCTGATCCATGATGATAGTTTGAC ATTTAAAGAAGACATTCAAAAAGCACAAGTGTCTGGACAAGGCGATAGTTTACATGAACATA TTGCAAATTTAGCTGGTAGCCCTGCTATTAAAAAAGGTATTTTACAGACTGTAAAAGTTGTT GATGAATTGGTCAAAGTAATGGGGCGGCATAAGCCAGAAAATATCGTTATTGAAATGGCACG TGAAAATCAGACAACTCAAAAGGGCCAGAAAAATTCGCGAGAGCGTATGAAACGAATCGAAG 20 AAGGTATCAAAGAATTAGGAAGTCAGATTCTTAAAGAGCATCCTGTTGAAAATACTCAATTG CAAAATGAAAAGCTCTATCTCTATTATCTCCAAAATGGAAGAGACATGTATGTGGACCAAGA ATTAGATATTAATCGTTTAAGTGATTATGATGTCGATCACATTGTTCCACAAAGTTTCCTTA AAGACGATTCAATAGACAATAAGGTCTTAACGCGTTCTGATAAAAATCGTGGTAAATCGGAT AACGTTCCAAGTGAAGAAGTAGTCAAAAAGATGAAAAACTATTGGAGACAACTTCTAAACGC 25 CAAGTTAATCACTCAACGTAAGTTTGATAATTTAACGAAAGCTGAACGTGGAGGTTTGAGTG AACTTGATAAAGCTGGTTTTATCAAACGCCAATTGGTTGAAACTCGCCAAATCACTAAGCAT GTGGCACAAATTTTGGATAGTCGCATGAATACTAAATACGATGAAAATGATAAACTTATTCG AGAGGTTAAAGTGATTACCTTAAAATCTAAATTAGTTTCTGACTTCCGAAAAGATTTCCAAT TCTATAAAGTACGTGAGATTAACAATTACCATCATGCCCATGATGCGTATCTAAATGCCGTC 30 GTTGGAACTGCTTTGATTAAGAAATATCCAAAACTTGAATCGGAGTTTGTCTATGGTGATTA TAAAGTTTATGATGTTCGTAAAATGATTGCTAAGTCTGAGCAAGAAATAGGCAAAGCAACCG CAAAATATTTCTTTTACTCTAATATCATGAACTTCTTCAAAACAGAAATTACACTTGCAAAT GGAGAGATTCGCAAACGCCCTCTAATCGAAACTAATGGGGAAACTGGAGAAATTGTCTGGGA TAAAGGGCGAGATTTTGCCACAGTGCGCAAAGTATTGTCCATGCCCCAAGTCAATATTGTCA 2020216484   17 Mar 2026 AGAAAACAGAAGTACAGACAGGCGGATTCTCCAAGGAGTCAATTTTACCAAAAAGAAATTCG GACAAGCTTATTGCTCGTAAAAAAGACTGGGATCCAAAAAAATATGGTGGTTTTGATAGTCC AACGGTAGCTTATTCAGTCCTAGTGGTTGCTAAGGTGGAAAAAGGGAAATCGAAGAAGTTAA AATCCGTTAAAGAGTTACTAGGGATCACAATTATGGAAAGAAGTTCCTTTGAAAAAAATCCG 5 ATTGACTTTTTAGAAGCTAAAGGATATAAGGAAGTTAAAAAAGACTTAATCATTAAACTACC TAAATATAGTCTTTTTGAGTTAGAAAACGGTCGTAAACGGATGCTGGCTAGTGCCGGAGAAT TACAAAAAGGAAATGAGCTGGCTCTGCCAAGCAAATATGTGAATTTTTTATATTTAGCTAGT CATTATGAAAAGTTGAAGGGTAGTCCAGAAGATAACGAACAAAAACAATTGTTTGTGGAGCA GCATAAGCATTATTTAGATGAGATTATTGAGCAAATCAGTGAATTTTCTAAGCGTGTTATTT 10 TAGCAGATGCCAATTTAGATAAAGTTCTTAGTGCATATAACAAACATAGAGACAAACCAATA CGTGAACAAGCAGAAAATATTATTCATTTATTTACGTTGACGAATCTTGGAGCTCCCGCTGC TTTTAAATATTTTGATACAACAATTGATCGTAAACGATATACGTCTACAAAAGAAGTTTTAG ATGCCACTCTTATCCATCAATCCATCACTGGTCTTTATGAAACACGCATTGATTTGAGTCAG CTAGGAGGTGACTGA 15 MDKKYSIGLDIGTNSVGWAVITDEYKVPSKKFKVLGNTDRHSIKKNLIGALLFDSGETAEAT RLKRTARRRYTRRKNRICYLQEIFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFGNIVD EVAYHEKYPTIYHLRKKLVDSTDKADLRLIYLALAHMIKFRGHFLIEGDLNPDNSDVDKLFI QLVQTYNQLFEENPINASGVDAKAILSARLSKSRRLENLIAQLPGEKKNGLFGNLIALSLGL 20 TPNFKSNFDLAEDAKLQLSKDTYDDDLDNLLAQIGDQYADLFLAAKNLSDAILLSDILRVNT EITKAPLSASMIKRYDEHHQDLTLLKALVRQQLPEKYKEIFFDQSKNGYAGYIDGGASQEEF YKFIKPILEKMDGTEELLVKLNREDLLRKQRTFDNGSIPHQIHLGELHAILRRQEDFYPFLK DNREKIEKILTFRIPYYVGPLARGNSRFAWMTRKSEETITPWNFEEVVDKGASAQSFIERMT NFDKNLPNEKVLPKHSLLYEYFTVYNELTKVKYVTEGMRKPAFLSGEQKKAIVDLLFKTNRK 25 VTVKQLKEDYFKKIECFDSVEISGVEDRFNASLGTYHDLLKIIKDKDFLDNEENEDILEDIV LTLTLFEDREMIEERLKTYAHLFDDKVMKQLKRRRYTGWGRLSRKLINGIRDKQSGKTILDF LKSDGFANRNFMQLIHDDSLTFKE DIQKAQVSGQGDSLHEHIANLAGSPAIKKGILQTVKVV DELVKVMGRHKPENIVIEMARENQTTQKGQKNSRERMKRIEEGIKELGSQILKEHPVENTQL QNEKLYLYYLQNGRDMYVDQELDINRLSDYDVDHIVPQSFLKDDSIDNKVLTRSDKNRGKSD 30 NVPSEEVVKKMKNYWRQLLNAKLITQRKFDNLTKAERGGLSELDKAGFIKRQLVETRQITKH VAQILDSRMNTKYDENDKLIREVKVITLKSKLVSDFRKDFQFYKVKEINNyHHAHDAyLNAV VGTALIKKYPKLESEFVYGDYKVYDVRKMIAKSEQEIGKATAKYFFYSNIMNFFKTEITLAN GEIRKRPLXETNGETGEIVWDKGRDFATVRKVLSMPQVNXVKKTEVQT GGFSKESILPKRNS DKLIARKKDWDPKKYGGFDSPTVAYSVLVVAKVEKGKSKKLKSVKELLGITIMERSSFEKNP 2020216484   17 Mar 2026 IDFLEAKGYKEVKKDLIIKLPKYSLFELENGRKRMLASAGELQKGNELALPSKYVNFLYLAS HYEKLKGSPEDNEQKQLFVEQHKHYLDEIIEQISEFSKRVILADANLDKVLSAYNKHRDKPI REQAENIIHLFTLTNLGAPAAFKYFDTTIDRKRYTSTKEVLDATLIHQSITGLYETRIDLSQ LGGD (single underline: HNH domain; double underline: RuvC domain) 5         In some embodiments, Cas9 refers to Cas9 from: Corynebacterium ulcerans (NCBI Refs: NC_015683.1, NC_017317.1); Corynebacterium diphtheria (NCBI Refs: NC_016782.1, NC_016786.1); Spiroplasma syrphidicola (NCBI Ref: NC_021284.1); Prevotella intermedia (NCBI Ref: NC_017861.1); Spiroplasma taiwanense (NCBI Ref: NC_021846.1); Streptococcus iniae (NCBI Ref: NC_021314.1); Belliella baltica (NCBI Ref: 10   NC_018010.1); Psychroflexus torquisI (NCBI Ref: NC_018721.1); Streptococcus thermophilus (NCBI Ref: YP_820832.1), Listeria innocua (NCBI Ref: NP_472073.1), Campylobacter jejuni (NCBI Ref: YP_002344900.1) or Neisseria meningitidis (NCBI Ref: YP_002342100.1) or to a Cas9 from any other organism. In some embodiments, dCas9 corresponds to, or comprises in part or in whole, a Cas9 15 amino acid sequence having one or more mutations that inactivate the Cas9 nuclease activity. For example, in some embodiments, a dCas9 domain comprises D10A and an H840A mutation or corresponding mutations in another Cas9. In some embodiments, the dCas9 comprises the amino acid sequence of dCas9 (D10A and H840A): 20 MDKKYSIGLAIGTNSVGWAVITDEYKVPSKKFKVLGNTDRHSIKKNLIGALLFDSGETAEAT RLKRTARRRYTRRKNRICYLQEIFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFGNIVD EVAYHEKYPTIYHLRKKLVDSTDKADLRLIYLALAHMIKFRGHFLIEGDLNPDNSDVDKLFI QLVQTYNQLFEENPINASGVDAKAILSARLSKSRRLENLIAQLPGEKKNGLFGNLIALSLGL TPNFKSNFDLAEDAKLQLSKDTYDDDLDNLLAQIGDQYADLFLAAKNLSDAILLSDILRVNT 25 EITKAPLSASMIKRYDEHHQDLTLLKALVRQQLPEKYKEIFFDQSKNGYAGYIDGGASQEEF YKFIKPILEKMDGTEELLVKLNREDLLRKQRTFDNGSIPHQIHLGELHAILRRQEDFYPFLK DNREKIEKILTFRIPYYVGPLARGNSRFAWMTRKSEETITPWNFEEVVDKGASAQSFIERMT NFDKNLPNEKVLPKHSLLYEYFTVYNELTKVKYVTEGMRKPAFLSGEQKKAIVDLLFKTNRK VTVKQLKEDYFKKIECFDSVEISGVEDRFNASLGTYHDLLKIIKDKDFLDNEENEDILEDIV 30 LTLTLFEDREMIEERLKTYAHLFDDKVMKQLKRRRYTGWGRLSRKLINGIRDKQSGKTILDF LKSDGFANRNFMQLIHDDSLTFKE DIQKAQVSGQGDSLHEHIANLAGSPAIKKGILQTVKVV DELVKVMGRHKPENIVIEMARENQTTQKGQKNSRERMKRIEEGIKELGSQILKEHPVENTQL QNEKLYLYYLQNGRDMYVDQELDINRLSDYDVDAIVPQSFLKDDSIDNKVLTRSDKNRGKSD NVPSEEVVKKMKNYWRQLLNAKLITQRKFDNLTKAERGGLSELDKAGFIKRQLVETRQITKH 2020216484   17 Mar 2026 VAQILDSRMNTKYDENDKLIREVKVITLKSKLVSDFRKDFQFYKVREINNyHHAHDAyLNAV VGTALIKKYPKLESEFVYGDYKVYDVRKMIAKSEQEIGKATAKYFFYSNIMNFFKTEITLAN GEIRKRPLIETNGETGEIVWDKGRDFATVRKVLSMPQVNIVKKTEVQTGGFSKESIL PKRNS DKLIARKKDWDPKKYGGFDSPTVAYSVLVVAKVEKGKSKKLKSVKELLGITIMERSSFEKNP 5 IDFLEAKGYKEVKKDLIIKLPKYSLFELENGRKRMLASAGELQKGNELALPSKYVNFLYLAS HYEKLKGSPEDNEQKQLFVEQHKHYLDEIIEQISEFSKRVILADANLDKVLSAYNKHRDKPI REQAENIIHLFTLTNLGAPAAFKYFDTTIDRKRYTSTKEVLDATLIHQSITGLYETRIDLSQ LGGD (single underline: HNH domain; double underline: RuvC domain). 10         In some embodiments, the Cas9 domain comprises a D10A mutation, while the residue at position 840 remains a histidine in the amino acid sequence provided above, or at corresponding positions in any of the amino acid sequences provided herein. In other embodiments, dCas9 variants having mutations other than D10A and H840A are provided, which, e.g., result in nuclease inactivated Cas9 (dCas9). Such mutations, by 15 way of example, include other amino acid substitutions at D10 and H840, or other substitutions within the nuclease domains of Cas9 (e.g., substitutions in the HNH nuclease subdomain and / or the RuvC1 subdomain). In some embodiments, variants or homologues of dCas9 are provided which are at least about 70% identical, at least about 80% identical, at least about 90% identical, at least about 95% identical, at least about 98% identical, at least 20 about 99% identical, at least about 99.5% identical, or at least about 99.9% identical. In some embodiments, variants of dCas9 are provided having amino acid sequences which are shorter, or longer, by about 5 amino acids, by about 10 amino acids, by about 15 amino acids, by about 20 amino acids, by about 25 amino acids, by about 30 amino acids, by about 40 amino acids, by about 50 amino acids, by about 75 amino acids, by about 100 amino acids or 25 more. In some embodiments, Cas9 fusion proteins as provided herein comprise the fulllength amino acid sequence of a Cas9 protein, e.g., one of the Cas9 sequences provided herein. In other embodiments, however, fusion proteins as provided herein do not comprise a full-length Cas9 sequence, but only one or more fragments thereof. Exemplary amino acid 30 sequences of suitable Cas9 domains and Cas9 fragments are provided herein, and additional suitable sequences of Cas9 domains and fragments will be apparent to those of skill in the art. It should be appreciated that additional Cas9 proteins (e.g., a nuclease dead Cas9 (dCas9), a Cas9 nickase (nCas9), or a nuclease active Cas9), including variants and homologs 2020216484   17 Mar 2026 thereof, are within the scope of this disclosure. Exemplary Cas9 proteins include, without limitation, those provided below. In some embodiments, the Cas9 protein is a nuclease dead Cas9 (dCas9). In some embodiments, the Cas9 protein is a Cas9 nickase (nCas9). In some embodiments, the Cas9 protein is a nuclease active Cas9. 5 Exemplary catalytically inactive Cas9 (dCas9): DKKYSIGLAIGTNSVGWAVITDEYKVPSKKFKVLGNTDRHSIKKNLIGALLFDSGETAEATR LKRTARRRYTRRKNRICYLQEIFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFGNIVDE VAYHEKYPTIYHLRKKLVDSTDKADLRLIYLALAHMIKFRGHFLIEGDLNPDNSDVDKLFIQ LVQTYNQLFEENPINASGVDAKAILSARLSKSRRLENLIAQLPGEKKNGLFGNLIALSLGLT 10 PNFKSNFDLAEDAKLQLSKDTYDDDLDNLLAQIGDQYADLFLAAKNLSDAILLSDILRVNTE ITKAPLSASMIKRYDEHHQDLTLLKALVRQQLPEKYKEIFFDQSKNGYAGYIDGGASQEEFY KFIKPILEKMDGTEELLVKLNREDLLRKQRTFDNGSIPHQIHLGELHAILRRQEDFYPFLKD NREKIEKILTFRIPYYVGPLARGNSRFAWMTRKSEETITPWNFEEVVDKGASAQSFIERMTN FDKNLPNEKVLPKHSLLYEYFTVYNELTKVKYVTEGMRKPAFLSGEQKKAIVDLLFKTNRKV 15 TVKQLKEDYFKKIECFDSVEISGVEDRFNASLGTYHDLLKIIKDKDFLDNEENEDILEDIVL TLTLFEDREMIEERLKTYAHLFDDKVMKQLKRRRYTGWGRLSRKLINGIRDKQSGKTILDFL KSDGFANRNFMQLIHDDSLTFKEDIQKAQVSGQGDSLHEHIANLAGSPAIKKGILQTVKVVD ELVKVMGRHKPENIVIEMARENQTTQKGQKNSRERMKRIEEGIKELGSQILKEHPVENTQLQ NEKLYLYYLQNGRDMYVDQELDINRLSDYDVDAIVPQSFLKDDSIDNKVLTRSDKNRGKSDN 20 VPSEEVVKKMKNYWRQLLNAKLITQRKFDNLTKAERGGLSELDKAGFIKRQLVETRQITKHV AQILDSRMNTKYDENDKLIREVKVITLKSKLVSDFRKDFQFYKVREINNYHHAHDAYLNAVV GTALIKKYPKLESEFVYGDYKVYDVRKMIAKSEQEIGKATAKYFFYSNIMNFFKTEITLANG EIRKRPLIETNGETGEIVWDKGRDFATVRKVLSMPQVNIVKKTEVQTGGFSKESILPKRNSD KLIARKKDWDPKKYGGFDSPTVAYSVLVVAKVEKGKSKKLKSVKELLGITIMERSSFEKNPI 25 DFLEAKGYKEVKKDLIIKLPKYSLFELENGRKRMLASAGELQKGNELALPSKYVNFLYLASH YEKLKGSPEDNEQKQLFVEQHKHYLDEIIEQISEFSKRVILADANLDKVLSAYNKHRDKPIR EQAENIIHLFTLTNLGAPAAFKYFDTTIDRKRYTSTKEVLDATLIHQSITGLYETRIDLSQL GGD 30 Exemplary catalytically Cas9 nickase (nCas9): DKKYSIGLAIGTNSVGWAVITDEYKVPSKKFKVLGNTDRHSIKKNLIGALLFDSGETAEATR LKRTARRRYTRRKNRICYLQEIFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFGNIVDE VAYHEKYPTIYHLRKKLVDSTDKADLRLIYLALAHMIKFRGHFLIEGDLNPDNSDVDKLFIQ LVQTYNQLFEENPINASGVDAKAILSARLSKSRRLENLIAQLPGEKKNGLFGNLIALSLGLT 2020216484   17 Mar 2026 PNFKSNFDLAEDAKLQLSKDTYDDDLDNLLAQIGDQYADLFLAAKNLSDAILLSDILRVNTE ITKAPLSASMIKRYDEHHQDLTLLKALVRQQLPEKYKEIFFDQSKNGYAGYIDGGASQEEFY KFIKPILEKMDGTEELLVKLNREDLLRKQRTFDNGSIPHQIHLGELHAILRRQEDFYPFLKD NREKIEKILTFRIPYYVGPLARGNSRFAWMTRKSEETITPWNFEEVVDKGASAQSFIERMTN 5 FDKNLPNEKVLPKHSLLYEYFTVYNELTKVKYVTEGMRKPAFLSGEQKKAIVDLLFKTNRKV TVKQLKEDYFKKIECFDSVEISGVEDRFNASLGTYHDLLKIIKDKDFLDNEENEDILEDIVL TLTLFEDREMIEERLKTYAHLFDDKVMKQLKRRRYTGWGRLSRKLINGIRDKQSGKTILDFL KSDGFANRNFMQLIHDDSLTFKEDIQKAQVSGQGDSLHEHIANLAGSPAIKKGILQTVKVVD ELVKVMGRHKPENIVIEMARENQTTQKGQKNSRERMKRIEEGIKELGSQILKEHPVENTQLQ 10 NEKLYLYYLQNGRDMYVDQELDINRLSDYDVDHIVPQSFLKDDSIDNKVLTRSDKNRGKSDN VPSEEVVKKMKNYWRQLLNAKLITQRKFDNLTKAERGGLSELDKAGFIKRQLVETRQITKHV AQILDSRMNTKYDENDKLIREVKVITLKSKLVSDFRKDFQFYKVREINNYHHAHDAYLNAVV GTALIKKYPKLESEFVYGDYKVYDVRKMIAKSEQEIGKATAKYFFYSNIMNFFKTEITLANG EIRKRPLIETNGETGEIVWDKGRDFATVRKVLSMPQVNIVKKTEVQTGGFSKESILPKRNSD 15 KLIARKKDWDPKKYGGFDSPTVAYSVLVVAKVEKGKSKKLKSVKELLGITIMERSSFEKNPI DFLEAKGYKEVKKDLIIKLPKYSLFELENGRKRMLASAGELQKGNELALPSKYVNFLYLASH YEKLKGSPEDNEQKQLFVEQHKHYLDEIIEQISEFSKRVILADANLDKVLSAYNKHRDKPIR EQAENIIHLFTLTNLGAPAAFKYFDTTIDRKRYTSTKEVLDATLIHQSITGLYETRIDLSQL GGD 20 Exemplary catalytically active Cas9: DKKYSIGLDIGTNSVGWAVITDEYKVPSKKFKVLGNTDRHSIKKNLIGALLFDSGETAEATR LKRTARRRYTRRKNRICYLQEIFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFGNIVDE VAYHEKYPTIYHLRKKLVDSTDKADLRLIYLALAHMIKFRGHFLIEGDLNPDNSDVDKLFIQ 25 LVQTYNQLFEENPINASGVDAKAILSARLSKSRRLENLIAQLPGEKKNGLFGNLIALSLGLT PNFKSNFDLAEDAKLQLSKDTYDDDLDNLLAQIGDQYADLFLAAKNLSDAILLSDILRVNTE ITKAPLSASMIKRYDEHHQDLTLLKALVRQQLPEKYKEIFFDQSKNGYAGYIDGGASQEEFY KFIKPILEKMDGTEELLVKLNREDLLRKQRTFDNGSIPHQIHLGELHAILRRQEDFYPFLKD NREKIEKILTFRIPYYVGPLARGNSRFAWMTRKSEETITPWNFEEVVDKGASAQSFIERMTN 30 FDKNLPNEKVLPKHSLLYEYFTVYNELTKVKYVTEGMRKPAFLSGEQKKAIVDLLFKTNRKV TVKQLKEDYFKKIECFDSVEISGVEDRFNASLGTYHDLLKIIKDKDFLDNEENEDILEDIVL TLTLFEDREMIEERLKTYAHLFDDKVMKQLKRRRYTGWGRLSRKLINGIRDKQSGKTILDFL KSDGFANRNFMQLIHDDSLTFKEDIQKAQVSGQGDSLHEHIANLAGSPAIKKGILQTVKVVD ELVKVMGRHKPENIVIEMARENQTTQKGQKNSRERMKRIEEGIKELGSQILKEHPVENTQLQ 2020216484   17 Mar 2026 NEKLYLYYLQNGRDMYVDQELDINRLSDYDVDHIVPQSFLKDDSIDNKVLTRSDKNRGKSDN VPSEEVVKKMKNYWRQLLNAKLITQRKFDNLTKAERGGLSELDKAGFIKRQLVETRQITKHV AQILDSRMNTKYDENDKLIREVKVITLKSKLVSDFRKDFQFYKVREINNYHHAHDAYLNAVV GTALIKKYPKLESEFVYGDYKVYDVRKMIAKSEQEIGKATAKYFFYSNIMNFFKTEITLANG 5 EIRKRPLIETNGETGEIVWDKGRDFATVRKVLSMPQVNIVKKTEVQTGGFSKESILPKRNSD KLIARKKDWDPKKYGGFDSPTVAYSVLVVAKVEKGKSKKLKSVKELLGITIMERSSFEKNPI DFLEAKGYKEVKKDLIIKLPKYSLFELENGRKRMLASAGELQKGNELALPSKYVNFLYLASH YEKLKGSPEDNEQKQLFVEQHKHYLDEIIEQISEFSKRVILADANLDKVLSAYNKHRDKPIR EQAENIIHLFTLTNLGAPAAFKYFDTTIDRKRYTSTKEVLDATLIHQSITGLYETRIDLSQL 10 GGD. In some embodiments, Cas9 refers to a Cas9 from archaea (e.g. nanoarchaea), which constitute a domain and kingdom of single-celled prokaryotic microbes. In some embodiments, Cas9 refers to CasX or CasY, which have been described in, for example, Burstein et al., "New CRISPR-Cas systems from uncultivated microbes." Cell Res. 2017 Feb 15   21. doi: 10.1038 / cr.2017.21, the entire contents of which is hereby incorporated by reference. Using genome-resolved metagenomics, a number of CRISPR-Cas systems were identified, including the first reported Cas9 in the archaeal domain of life. This divergent Cas9 protein was found in little- studied nanoarchaea as part of an active CRISPR-Cas system. In bacteria, two previously unknown systems were discovered, CRISPR-CasX and CRISPR-CasY, which 20 are among the most compact systems yet discovered. In some embodiments, Cas9 refers to CasX, or a variant of CasX. In some embodiments, Cas9 refers to a CasY, or a variant of CasY. It should be appreciated that other RNA-guided DNA binding proteins may be used as a nucleic acid programmable DNA binding protein (napDNAbp), and are within the scope of this disclosure. 25          In particular embodiments, napDNAbps useful in the methods of the disclosure include circular permutants, which are known in the art and described, for example, by Oakes et al., Cell 176, 254-267, 2019. An exemplary circular permutant follows where the bold sequence indicates sequence derived from Cas9, the italics sequence denotes a linker sequence, and the underlined sequence denotes a bipartite nuclear localization sequence, 30 CP5 (with MSP “NGC=Pam Variant with mutations Regular Cas9 likes NGG” PID=Protein Interacting Domain and “D10A” nickase): EIGKATAKYFFYSNIMNFFKTEITLANGEIRKRPLIETNGETGEIVWDKGRDFATVRKVLSM PQVNIVKKTEVQTGGFSKESILPKRNSDKLIARKKDWDPKKYGGFMQPTVAYSVLVVAKVEK 2020216484   17 Mar 2026 GKSKKLKSVKELLGITIMERSSFEKNPIDFLEAKGYKEVKKDLIIKLPKYSLFELENGRKRM LASAKFLQKGNELALPSKYVNFLYLASHYEKLKGSPEDNEQKQLFVEQHKHYLDEIIEQISE FSKRVILADANLDKVLSAYNKHRDKPIREQAENIIHLFTLTNLGAPRAFKYFDTTIARKEYR STKEVLDATLIHQSITGLYETRIDLSQLGGDGGSGGSGGSGGSGGSGGSGGMDKKYSIGLAI 5 GTNSVGWAVITDEYKVPSKKFKVLGNTDRHSIKKNLIGALLFDSGETAEATRLKRTARRRYT RRKNRICYLQEIFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFGNIVDEVAYHEKYPTI YHLRKKLVDSTDKADLRLIYLALAHMIKFRGHFLIEGDLNPDNSDVDKLFIQLVQTYNQLFE ENPINASGVDAKAILSARLSKSRRLENLIAQLPGEKKNGLFGNLIALSLGLTPNFKSNFDLA EDAKLQLSKDTYDDDLDNLLAQIGDQYADLFLAAKNLSDAILLSDILRVNTEITKAPLSASM 10 IKRYDEHHQDLTLLKALVRQQLPEKYKEIFFDQSKNGYAGYIDGGASQEEFYKFIKPILEKM DGTEELLVKLNREDLLRKQRTFDNGSIPHQIHLGELHAILRRQEDFYPFLKDNREKIEKILT FRIPYYVGPLARGNSRFAWMTRKSEETITPWNFEEVVDKGASAQSFIERMTNFDKNLPNEKV LPKHSLLYEYFTVYNELTKVKYVTEGMRKPAFLSGEQKKAIVDLLFKTNRKVTVKQLKEDYF KKIECFDSVEISGVEDRFNASLGTYHDLLKIIKDKDFLDNEENEDILEDIVLTLTLFEDREM 15 IEERLKTYAHLFDDKVMKQLKRRRYTGWGRLSRKLINGIRDKQSGKTILDFLKSDGFANRNF MQLIHDDSLTFKEDIQKAQVSGQGDSLHEHIANLAGSPAIKKGILQTVKVVDELVKVMGRHK PENIVIEMARENQTTQKGQKNSRERMKRIEEGIKELGSQILKEHPVENTQLQNEKLYLYYLQ NGRDMYVDQELDINRLSDYDVDHIVPQSFLKDDSIDNKVLTRSDKNRGKSDNVPSEEVVKKM KNYWRQLLNAKLITQRKFDNLTKAERGGLSELDKAGFIKRQLVETRQITKHVAQILDSRMNT 20 KYDENDKLIREVKVITLKSKLVSDFRKDFQFYKVREINNYHHAHDAYLNAVVGTALIKKYPK LESEFVYGDYKVYDVRKMIAKSEQEGADKRTADGSEFESPKKKRKV* Non-limiting examples of a polynucleotide programmable nucleotide binding domain which can be incorporated into a base editor include a CRISPR protein-derived domain, a restriction nuclease, a meganuclease, TAL nuclease (TALEN), and a zinc finger nuclease 25 (ZFN). In some embodiments, the nucleic acid programmable DNA binding protein (napDNAbp) of any of the fusion proteins provided herein may be a CasX or CasY protein. In some embodiments, the napDNAbp is a CasX protein. In some embodiments, the napDNAbp is a CasY protein. In some embodiments, the napDNAbp comprises an amino 30   acid sequence that is at least 85%, at least 90%, at least 91%, at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at ease 99.5% identical to a naturally-occurring CasX or CasY protein. In some embodiments, the napDNAbp is a naturally-occurring CasX or CasY protein. In some embodiments, the napDNAbp comprises an amino acid sequence that is at least 85%, at least 90%, at least 91%, 2020216484   17 Mar 2026 at least 92%, at least 93%, at least 94%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at ease 99.5% identical to any CasX or CasY protein described herein. It should be appreciated that Cas12b / C2c1, CasX and CasY from other bacterial species may also be used in accordance with the present disclosure. 5 Cas12b / C2c1 (uniprot.org / uniprot / T0D7A2#2) sp|T0D7A2|C2C1_ALIAG CRISPR-associated endo- nuclease C2c1 OS = Alicyclobacillus acido- terrestris (strain ATCC 49025 / DSM 3922 / CIP 106132 / NCIMB 13137 / GD3B) GN=c2c1 PE=1 SV=1 10 MAVKSIKVKLRLDDMPEIRAGLWKLHKEVNAGVRYYTEWLSLLRQENLYRRSPNGDGEQECD KTAEECKAELLERLRARQVENGHRGPAGSDDELLQLARQLYELLVPQAIGAKGDAQQIARKF LSPLADKDAVGGLGIAKAGNKPRWVRMREAGEPGWEEEKEKAETRKSADRTADVLRALADFG LKPLMRVYTDSEMSSVEWKPLRKGQAVRTWDRDMFQQAIERMMSWESWNQRVGQEYAKLVEQ KNRFEQKNFVGQEHLVHLVNQLQQDMKEASPGLESKEQTAHYVTGRALRGSDKVFEKWGKLA 15 PDAPFDLYDAEIKNVQRRNTRRFGSHDLFAKLAEPEYQALWREDASFLTRYAVYNSILRKLN HAKMFATFTLPDATAHPIWTRFDKLGGNLHQYTFLFNEFGERRHAIRFHKLLKVENGVAREV DDVTVPISMSEQLDNLLPRDPNEPIALYFRDYGAEQHFTGEFGGAKIQCRRDQLAHMHRRRG ARDVYLNVSVRVQSQSEARGERRPPYAAVFRLVGDNHRAFVHFDKLSDYLAEHPDDGKLGSE GLLSGLRVMSVDLGLRTSASISVFRVARKDELKPNSKGRVPFFFPIKGNDNLVAVHERSQLL 20 KLPGETESKDLRAIREERQRTLRQLRTQLAYLRLLVRCGSEDVGRRERSWAKLIEQPVDAAN HMTPDWREAFENELQKLKSLHGICSDKEWMDAVYESVRRVWRHMGKQVRDWRKDVRSGERPK IRGYAKDVVGGNSIEQIEYLERQYKFLKSWSFFGKVSGQVIRAEKGSRFAITLREHIDHAKE DRLKKLADRIIMEALGYVYALDERGKGKWVAKYPPCQLILLEELSEYQFNNDRPPSENNQLM QWSHRGVFQELINQAQVHDLLVGTMYAAFSSRFDARTGAPGIRCRRVPARCTQEHNPEPFPW 25 WLNKFVVEHTLDACPLRADDLIPTGEGEIFVSPFSAEEGDFHQIHADLNAAQNLQQRLWSDF DISQIRLRCDWGEVDGELVLIPRLTGKRTADSYSNKVFYTNTGVTYYERERGKKRRKVFAQE KLSEEEAELLVEADEAREKSVVLMRDPSGIINRGNWTRQKEFWSMV NQRIEGYLVKQIRSR VPLQDSACENTGDI 30 CasX (uniprot.org / uniprot / F0NN87; uniprot.org / uniprot / F0NH53) >tr|F0NN87|F0NN87_SULIH CRISPR-associated Casx protein OS = Sulfolobus islandicus (strain HVE10 / 4) GN = SiH_0402 PE=4 SV=1 MEVPLYNIFGDNYIIQVATEAENSTIYNNKVEIDDEELRNVLNLAYKIAKNNEDAAAERRGK AKKKKGEEGETTTSNIILPLSGNDKNPWTETLKCYNFPTTVALSEVFKNFSQVKECEEVSAP 2020216484   17 Mar 2026 SFVKPEFYEFGRSPGMVERTRRVKLEVEPHYLIIAAAGWVLTRLGKAKVSEGDYVGVNVFTP TRGILYSLIQNVNGIVPGIKPETAFGLWIARKVVSSVTNPNVSVVRIYTISDAVGQNPTTIN GGFSIDLTKLLEKRYLLSERLEAIARNALSISSNMRERYIVLANYIYEYLTG SKRLEDLLY FANRDLIMNLNSDDGKVRDLKLISAYVNGELIRGEG 5 >tr|F0NH53|F0NH53_SULIR CRISPR associated protein, Casx OS = Sulfolobus islandicus (strain REY15A) GN=SiRe_0771 PE=4 SV=1 MEVPLYNIFGDNYIIQVATEAENSTIYNNKVEIDDEELRNVLNLAYKIAKNNEDAAAERRGK AKKKKGEEGETTTSNIILPLSGNDKNPWTETLKCYNFPTTVALSEVFKNFSQVKECEEVSAP 10 SFVKPEFYKFGRSPGMVERTRRVKLEVEPHYLIMAAAGWVLTRLGKAKVSEGDYVGVNVFTP TRGILYSLIQNVNGIVPGIKPETAFGLWIARKVVSSVTNPNVSVVSIYTISDAVGQNPTTIN GGFSIDLTKLLEKRDLLSERLEAIARNALSISSNMRERYIVLANYIYEYLTGSKRLEDLLYF ANRDLIMNLNSDDGKVRDLKLISAYVNGELIRGEG 15 Deltaproteobacteria CasX MEKRINKIRKKLSADNATKPVSRSGPMKTLLVRVMTDDLKKRLEKRRKKPEVMPQVISNNAA NNLRMLLDDYTKMKEAILQVYWQEFKDDHVGLMCKFAQPASKKIDQNKLKPEMDEKGNLTTA GFACSQCGQPLFVYKLEQVSEKGKAYTNYFGRCNVAEHEKLILLAQLKPVKDSDEAVTYSLG KFGQRALDFYSIHVTKESTHPVKPLAQIAGNRYASGPVGKALSDACMGTIASFLSKYQDIII 20 EHQKVVKGNQKRLESLRELAGKENLEYPSVTLPPQPHTKEGVDAYNEVIARVRMWVNLNLWQ KLKLSRDDAKPLLRLKGFPSFPVVERRENEVDWWNTINEVKKLIDAKRDMGRVFWSGVTAEK RNTILEGYNYLPNENDHKKREGSLENPKKPAKRQFGDLLLYLEKKYAGDWGKVFDEAWERID KKIAGLTSHIEREEARNAEDAQSKAVLTDWLRAKASFVLERLKEMDEKEFYACEIQLQKWYG DLRGNPFAVEAENRVVDISGFSIGSDGHSIQYRNLLAWKYLENGKREFYLLMNYGKKGRIRF 25 TDGTDIKKSGKWQGLLYGGGKAKVIDLTFDPDDEQLIILPLAFGTRQGREFIWNDLLSLETG LIKLANGRVIEKTIYNKKIGRDEPALFVALTFERREVVDPSNIKPVNLIGVARGENIPAVIA LTDPEGCPLPEFKDSSGGPTDILRIGEGYKEKQRAIQAAKEVEQRRAGGYSRKFASKSRNLA DDMVRNSARDLFYHAVTHDAVLVFANLSRGFGRQGKRTFMTERQYTKMEDWLTAKLAYEGLT SKTYLSKTLAQYTSKTCSNCGFTITYADMDVMLVRLKKTSDGWATTLNNKELKAEYQITYYN 30 RYKRQTVEKELSAELDRLSEESGNNDISKWTKGRRDEALFLLKKRFSHRPVQEQFVCLDCGH EVHAAEQAALNIARSWLFLNSNSTEFKSYKSGKQPFVGAWQAFYKRRLKEVWKPNA CasY (ncbi.nlm.nih.gov / protein / APG80656.1) 2020216484   17 Mar 2026 >APG80656.1 CRISPR-associated protein CasY (uncultured Parcubacteria group bacterium] MSKRHPRISGVKGYRLHAQRLEYTGKSGAMRTIKYPLYSSPSGGRTVPREIVSAINDDYVGL YGLSNFDDLYNAEKRNEEKVYSVLDFWYDCVQYGAVFSYTAPGLLKNVAEVRGGSYELTKTL 5 KGSHLYDELQIDKVIKFLNKKEISRANGSLDKLKKDIIDCFKAEYRERHKDQCNKLADDIKN AKKDAGASLGERQKKLFRDFFGISEQSENDKPSFTNPLNLTCCLLPFDTVNNNRNRGEVLFN KLKEYAQKLDKNEGSLEMWEYIGIGNSGTAFSNFLGEGFLGRLRENKITELKKAMMDITDAW RGQEQEEELEKRLRILAALTIKLREPKFDNHWGGYRSDINGKLSSWLQNYINQTVKIKEDLK GHKKDLKKAKEMINRFGESDTKEEAVVSSLLESIEKIVPDDSADDEKPDIPAIAIYRRFLSD 10 GRLTLNRFVQREDVQEALIKERLEAEKKKKPKKRKKKSDAEDEKETIDFKELFPHLAKPLKL VPNFYGDSKRELYKKYKNAAIYTDALWKAVEKIYKSAFSSSLKNSFFDTDFDKDFFIKRLQK IFSVYRRFNTDKWKPIVKNSFAPYCDIVSLAENEVLYKPKQSRSRKSAAIDKNRVRLPSTEN IAKAGIALARELSVAGFDWKDLLKKEEHEEYIDLIELHKTALALLLAVTETQLDISALDFVE NGTVKDFMKTRDGNLVLEGRFLEMFSQSIVFSELRGLAGLMSRKEFITRSAIQTMNGKQAEL 15 LYIPHEFQSAKITTPKEMSRAFLDLAPAEFATSLEPESLSEKSLLKLKQMRYYPHYFGYELT RTGQGIDGGVAENALRLEKSPVKKREIKCKQYKTLGRGQNKIVLYVRSSYYQTQFLEWFLHR PKNVQTDVAVSGSFLIDEKKVKTRWNYDALTVALEPVSGSERVFVSQPFTIFPEKSAEEEGQ RYLGIDIGEYGIAYTALEITGDSAKILDQNFISDPQLKTLREEVKGLKLDQRRGTFAMPSTK IARIRESLVHSLRNRIHHLALKHKAKIVYELEVSRFEEGKQKIKKVYATLKKADVYSEIDAD 20 KNLQTTVWGKLAVASEISASYTSQFCGACKKLWRAEMQVDETITTQELIGTVRVIKGGTLID AIKDFMRPPIFDENDTPFPKYRDFCDKHHISKKMRGNSCLFICPFCRANADADIQASQTIAL LRYVKEEKKVEDYFERFRKLKN IKVLGQMKKI The term “conservative amino acid substitution” or “conservative mutation” refers to the replacement of one amino acid by another amino acid with a common property. A 25   functional way to define common properties between individual amino acids is to analyze the normalized frequencies of amino acid changes between corresponding proteins of homologous organisms (Schulz, G. E. and Schirmer, R. H., Principles of Protein Structure, Springer-Verlag, New York (1979)). According to such analyses, groups of amino acids can be defined where amino acids within a group exchange preferentially with each other, and 30 therefore resemble each other most in their impact on the overall protein structure (Schulz, G. E. and Schirmer, R. H., supra). Non-limiting examples of conservative mutations include amino acid substitutions of amino acids, for example, lysine for arginine and vice versa such that a positive charge can be maintained; glutamic acid for aspartic acid and vice versa such 2020216484   17 Mar 2026 that a negative charge can be maintained; serine for threonine such that a free -OH can be maintained; and glutamine for asparagine such that a free -NH2 can be maintained. The term “coding sequence” or “protein coding sequence” as used interchangeably herein refers to a segment of a polynucleotide that codes for a protein. The region or 5 sequence is bounded nearer the 5’ end by a start codon and nearer the 3’ end with a stop codon. Coding sequences can also be referred to as open reading frames. By “cytidine deaminase” is meant a polypeptide or fragment thereof capable of catalyzing a deamination reaction that converts an amino group to a carbonyl group. In one embodiment, the cytidine deaminase converts cytosine to uracil or 5-methylcytosine to 10 thymine. The cytidine deaminase (e.g., engineered cytidine deaminase, evolved cytidine deaminase) provided herein can be from any organism, such as a bacterium. In some embodiments, a cytidine deaminase of a base editor can comprise all or a portion of an apolipoprotein B mRNA editing complex (APOBEC) family deaminase. APOBEC is a family of evolutionarily conserved cytidine deaminases. Members of this 15 family are C-to-U editing enzymes. In some embodiments, the cytidine deaminase includes, without limitation: APOBEC family members, including but not limited to: APOBEC1, APOBEC2, APOBEC3A, APOBEC3B, APOBEC3C, APOBEC3D ("APOBEC3E" now refers to this), APOBEC3F, APOBEC3G, APOBEC3H, APOBEC4, Activation-induced (cytidine) deaminase (AID), hAPOBEC1, which is derived from Homo sapiens, rAPOBEC1, 20 which is derived from Rattus norvegicus, ppAPOBEC1, which is derived from Pongo pygmaeus, AmAPOBEC1 (BEM3.31), derived from Alligator mississippiensis, ocAPOBEC1, which is derived from Oryctolagus cuniculus, SsAPOBEC2 (BEM3.39), which is derived from Sus scrofa, hAPOBEC3A, which is derived from Homo sapiens, maAPOBEC1, which is derived from Mesocricetus auratus, mdAPOBEC1, which is derived 25   from Monodelphis domestica; cytidine deaminase 1 (CDA1), hA3A, which is APOBEC3A derived from Homo sapiens, RrA3F (BEM3.14), which is APOBEC3F derived from Rhinopithecus roxellana; PmCDA1, which is derived from Petromyzon marinus (Petromyzon marinus cytosine deaminase 1, “PmCDA1”); AID (Activation-induced cytidine deaminase; AICDA), which is derived from a mammal (e.g., human, swine, bovine, horse, monkey etc.); 30 hAID, which is derived from Homo sapiens; and FENRY. The term “deaminase” or “deaminase domain,” as used herein, refers to a protein or enzyme that catalyzes a deamination reaction. In some embodiments, the deaminase or deaminase domain is a cytidine deaminase, catalyzing the hydrolytic deamination of cytidine 2020216484   17 Mar 2026 or deoxycytidine to uridine or deoxyuridine, respectively. In some embodiments, the deaminase or deaminase domain is a cytosine deaminase, catalyzing the hydrolytic deamination of cytosine to uracil. In some embodiments, the deaminase is an adenosine deaminase, which catalyzes the hydrolytic deamination of adenine to hypoxanthine. In some 5 embodiments, the deaminase is an adenosine deaminase, which catalyzes the hydrolytic deamination of adenosine or adenine (A) to inosine (I). In some embodiments, the deaminase or deaminase domain is an adenosine deaminase catalyzing the hydrolytic deamination of adenosine or deoxyadenosine to inosine or deoxyinosine, respectively. In some embodiments, the adenosine deaminase catalyzes the hydrolytic deamination of adenosine in 10 deoxyribonucleic acid (DNA). The deaminases (e.g., engineered deaminases, evolved deaminases) provided herein can be from any organism, such as a bacterium. In some embodiments, the deaminase is from a bacterium, such as Escherichia coli, Staphylococcus aureus, Salmonella typhimurium, Shewanella putrefaciens, Haemophilus influenzae, or Caulobacter crescentus. 15           “Detect” refers to identifying the presence, absence or amount of the analyte to be detected. In one embodiment, a sequence alteration in a polynucleotide or polypeptide is detected. In another embodiment, the presence of indels is detected. By "detectable label" is meant a composition that when linked to a molecule of interest renders the latter detectable, via spectroscopic, photochemical, biochemical, 20 immunochemical, or chemical means. For example, useful labels include radioactive isotopes, magnetic beads, metallic beads, colloidal particles, fluorescent dyes, electron-dense reagents, enzymes (for example, as commonly used in an enzyme linked immunosorbent assay (ELISA)), biotin, digoxigenin, or haptens. By “disease” is meant any condition or disorder that damages or interferes with the 25 normal function of a cell, tissue, or organ. The term “effective amount,” as used herein, refers to an amount of a biologically active agent that is sufficient to elicit a desired biological response. The effective amount of an active agent(s) used to practice the therapeutic treatment of a disease varies depending upon the manner of administration, the age, body weight, and general health of the subject. 30 Ultimately, the attending physician or veterinarian will decide the appropriate amount and dosage regimen. Such amount is referred to as an “effective” amount. In one embodiment, an effective amount is the amount of a base editor of the disclosure (e.g., a fusion protein comprising a programable DNA binding protein, a nucleobase editor and gRNA) sufficient to 2020216484   17 Mar 2026 introduce an alteration in a gene of interest in a cell (e.g., a cell in vitro or in vivo). In some embodiments, an effective amount of a fusion protein provided herein, e.g., of a multieffector nucleobase editor comprising a nCas9 domain and one or more deaminase domains (e.g., adenosine deaminase, cytidine deaminase) may refer to the amount of the fusion protein 5 that is sufficient to induce editing of a target site specifically bound and edited by the multi effector nucleobase editors. In one embodiment, an effective amount is the amount of a base editor required to achieve a therapeutic effect (e.g., to reduce or control a disease or a symptom or condition thereof). Such therapeutic effect need not be sufficient to alter a gene of interest in all cells of a subject, tissue or organ, but only to alter a gene of interest in about 10   1%, 5%, 10%, 25%, 50%, 75% or more of the cells present in a subject, tissue or organ. In some embodiments, an effective amount of a fusion protein provided herein, e.g., of a nucleobase editor comprising a nCas9 domain and one or more deaminase domains (e.g., adenosine deaminase, cytidine deaminase) refers to the amount of the fusion protein that is sufficient to induce editing of a target site specifically bound and edited by the nucleobase 15 editors described herein. As will be appreciated by the skilled artisan, the effective amount of an agent, e.g., a fusion protein, a nuclease, a hybrid protein, a protein dimer, a complex of a protein (or protein dimer) and a polynucleotide, or a polynucleotide, may vary depending on various factors as, for example, on the desired biological response, e.g., on the specific allele, genome, or target site to be edited, on the cell or tissue being targeted, and / or on the 20 agent being used. By "fragment" is meant a portion of a polypeptide or nucleic acid molecule. This portion contains, at least about 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, or 90% of the entire length of the reference nucleic acid molecule or polypeptide. A fragment may contain 10, 20, 30, 40, 50, 60, 70, 80, 90, or 100, 200, 300, 400, 500, 600, 700, 800, 900, or 1000 25 nucleotides or amino acids. By “guide RNA” or “gRNA” is meant a polynucleotide which can be specific for a target sequence and can form a complex with a polynucleotide programmable nucleotide binding domain protein (e.g., Cas9 or Cpf1). In an embodiment, the guide polynucleotide is a guide RNA (gRNA). gRNAs can exist as a complex of two or more RNAs, or as a single 30 RNA molecule. gRNAs that exist as a single RNA molecule may be referred to as singleguide RNAs (sgRNAs), though “gRNA” is used interchangeably to refer to guide RNAs that exist as either single molecules or as a complex of two or more molecules. Typically, gRNAs that exist as single RNA species comprise two domains: (1) a domain that shares homology 2020216484   17 Mar 2026 to a target nucleic acid (e.g., and directs binding of a Cas9 complex to the target); and (2) a domain that binds a Cas9 protein. In some embodiments, domain (2) corresponds to a sequence known as a tracrRNA, and comprises a stem-loop structure. For example, in some embodiments, domain (2) is identical or homologous to a tracrRNA as provided in Jinek et 5   al., Science 337:816-821(2012), the entire contents of which is incorporated herein by reference. Other examples of gRNAs (e.g., those including domain 2) can be found in U.S. Provisional Patent Application, U.S.S.N. 61 / 874,682, filed September 6, 2013, entitled "Switchable Cas9 Nucleases and Uses Thereof," and U.S. Provisional Patent Application, U.S.S.N. 61 / 874,746, filed September 6, 2013, entitled "Delivery System For Functional 10 Nucleases," the entire contents of each are hereby incorporated by reference in their entirety. In some embodiments, a gRNA comprises two or more of domains (1) and (2), and may be referred to as an “extended gRNA.” An extended gRNA will bind two or more Cas9 proteins and bind a target nucleic acid at two or more distinct regions, as described herein. The gRNA comprises a nucleotide sequence that complements a target site, which mediates binding of 15 the nuclease / RNA complex to said target site, providing the sequence specificity of the nuclease:RNA complex. “Hybridization” means hydrogen bonding, which may be Watson-Crick, Hoogsteen or reversed Hoogsteen hydrogen bonding, between complementary nucleobases. For example, adenine and thymine are complementary nucleobases that pair through the 20 formation of hydrogen bonds. The term "inhibitor of base repair" or "IBR" refers to a protein that is capable in inhibiting the activity of a nucleic acid repair enzyme, for example a base excision repair (BER) enzyme. In some embodiments, the IBR is an inhibitor of inosine base excision repair. Exemplary inhibitors of base repair include inhibitors of APE1, Endo III, Endo IV, 25 Endo V, Endo VIII, Fpg, hOGGl, hNEILl, T7 Endol, T4PDG, UDG, hSMUGl, and hAAG. In some embodiments, the IBR is an inhibitor of Endo V or hAAG. In some embodiments, the IBR is a catalytically inactive EndoV or a catalytically inactive hAAG. In some embodiments, the base repair inhibitor is an inhibitor of Endo V or hAAG. In some embodiments, the base repair inhibitor is a catalytically inactive EndoV or a catalytically 30 inactive hAAG. In some embodiments, the base repair inhibitor is uracil glycosylase inhibitor (UGI). UGI refers to a protein that is capable of inhibiting a uracil-DNA glycosylase base-excision repair enzyme. In some embodiments, a UGI domain comprises a wild-type UGI or a 2020216484   17 Mar 2026 fragment of a wild-type UGI. In some embodiments, the UGI proteins provided herein include fragments of UGI and proteins homologous to a UGI or a UGI fragment. In some embodiments, the base repair inhibitor is an inhibitor of inosine base excision repair. In some embodiments, the base repair inhibitor is a “catalytically inactive inosine specific nuclease” 5 or “dead inosine specific nuclease. Without wishing to be bound by any particular theory, catalytically inactive inosine glycosylases (e.g., alkyl adenine glycosylase (AAG)) can bind inosine, but cannot create an abasic site or remove the inosine, thereby sterically blocking the newly formed inosine moiety from DNA damage / repair mechanisms. In some embodiments, the catalytically inactive inosine specific nuclease can be capable of binding an inosine in a 10 nucleic acid but does not cleave the nucleic acid. Non-limiting exemplary catalytically inactive inosine specific nucleases include catalytically inactive alkyl adenosine glycosylase (AAG nuclease), for example, from a human, and catalytically inactive endonuclease V (EndoV nuclease), for example, from E. coli. In some embodiments, the catalytically inactive AAG nuclease comprises an E125Q mutation or a corresponding mutation in another 15 AAG nuclease. By “increases” is meant a positive alteration of at least 10%, 25%, 50%, 75%, or 100%. An "intein" is a fragment of a protein that is able to excise itself and join the remaining fragments (the exteins) with a peptide bond in a process known as protein splicing. 20 Inteins are also referred to as "protein introns." The process of an intein excising itself and joining the remaining portions of the protein is herein termed "protein splicing" or "intein-mediated protein splicing." In some embodiments, an intein of a precursor protein (an intein containing protein prior to intein-mediated protein splicing) comes from two genes. Such intein is referred to herein as a split intein (e.g., split intein-N and split intein-C). For 25 example, in cyanobacteria, DnaE, the catalytic subunit a of DNA polymerase III, is encoded by two separate genes, dnaE-n and dnaE-c. The intein encoded by the dnaE-n gene may be herein referred as "intein-N." The intein encoded by the dnaE-c gene may be herein referred as "intein-C." Other intein systems may also be used. For example, a synthetic intein based on the 30 dnaE intein, the Cfa-N (e.g., split intein-N) and Cfa-C (e.g., split intein-C) intein pair, has been described (e.g., in Stevens et al., J Am Chem Soc. 2016 Feb. 24; 138(7):2162-5, incorporated herein by reference). Non-limiting examples of intein pairs that may be used in accordance with the present disclosure include: Cfa DnaE intein, Ssp GyrB intein, Ssp DnaX 2020216484   17 Mar 2026 intein, Ter DnaE3 intein, Ter ThyX intein, Rma DnaB intein and Cne Prp8 intein (e.g., as described in U.S. Patent No. 8,394,604, incorporated herein by reference. Exemplary nucleotide and amino acid sequences of inteins are provided. DnaE Intein-N DNA: 5 TGCCTGTCATACGAAACCGAGATACTGACAGTAGAATATGGCCTTCTGCCAATCGGGAAGAT TGTGGAGAAACGGATAGAATGCACAGTTTACTCTGTCGATAACAATGGTAACATTTATACTC AGCCAGTTGCCCAGTGGCACGACCGGGGAGAGCAGGAAGTATTCGAATACTGTCTGGAGGAT GGAAGTCTCATTAGGGCCACTAAGGACCACAAATTTATGACAGTCGATGGCCAGATGCTGCC TATAGACGAAATCTTTGAGCGAGAGTTGGACCTCATGCGAGTTGACAACCTTCCTAAT 10 DnaE Intein-N Protein: CLSYETEILTVEYGLLPIGKIVEKRIECTVYSVDNNGNIYTQPVAQWHDR GEQEVFEYCLEDGSLIRATKDHKFMTVDGQMLPIDEIFERELDLMRVDNLPN DnaE Intein-C DNA: ATGATCAAGATAGCTACAAGGAAGTATCTTGGCAAACAAAACGTTTATGA 15 TATTGGAGTCGAAAGAGATCACAACTTTGCTCTGAAGAACGGATTCATAGCTTCTAAT Intein-C: MIKIATRKYLGKQNVYDIGVERDHNFALKNGFIASN Cfa-N DNA: TGCCTGTCTTATGATACCGAGATACTTACCGTTGAATATGGCTTCTTGCCTATTGGAAAGAT TGTCGAAGAGAGAATTGAATGCACAGTATATACTGTAGACAAGAATGGTTTCGTTTACACAC 20 AGCCCATTGCTCAATGGCACAATCGCGGCGAACAAGAAGTATTTGAGTACTGTCTCGAGGAT GGAAGCATCATACGAGCAACTAAAGATCATAAATTCATGACCACTGACGGGCAGATGTTGCC AATAGATGAGATATTCGAGCGGGGCTTGGATCTCAAACAAGTGGATGGATTGCCA Cfa-N Protein: CLSYDTEILTVEYGFLPIGKIVEERIECTVYTVDKNGFVYTQPIAQWHNRGEQEVFEYCLED 25 GSIIRATKDHKFMTTDGQMLPIDEIFERGLDLKQVDGLP Cfa-C DNA: ATGAAGAGGACTGCCGATGGATCAGAGTTTGAATCTCCCAAGAAGAAGAGGAAAGTAAAGAT AATATCTCGAAAAAGTCTTGGTACCCAAAATGTCTATGATATTGGAGTGGAGAAAGATCACA ACTTCCTTCTCAAGAACGGTCTCGTAGCCAGCAAC 30 Cfa-C Protein: MKRTADGSEFESPKKKRKVKIISRKSLGTQNVYDIGVEKDHNFLLKNGLVASN Intein-N and intein-C may be fused to the N-terminal portion of the split Cas9 and the C-terminal portion of the split Cas9, respectively, for the joining of the N-terminal portion of the split Cas9 and the C-terminal portion of the split Cas9. For example, in some 2020216484   17 Mar 2026 embodiments, an intein-N is fused to the C-terminus of the N-terminal portion of the split Cas9, i.e., to form a structure of N--[N-terminal portion of the split Cas9]-[intein-N]--C. In some embodiments, an intein-C is fused to the N-terminus of the C-terminal portion of the split Cas9, i.e., to form a structure of N-[intein-C]--[C-terminal portion of the split Cas9]-C. 5 The mechanism of intein-mediated protein splicing for joining the proteins the inteins are fused to (e.g., split Cas9) is known in the art, e.g., as described in Shah et al., Chem Sci. 2014; 5(1):446-461, incorporated herein by reference. Methods for designing and using inteins are known in the art and described, for example by WO2014004336, WO2017132580, US20150344549, and US20180127780, each of which is incorporated herein by reference in 10 their entirety. The terms "isolated," "purified," or "biologically pure" refer to material that is free to varying degrees from components which normally accompany it as found in its native state. "Isolate" denotes a degree of separation from original source or surroundings. "Purify" denotes a degree of separation that is higher than isolation. A "purified" or "biologically 15 pure" protein is sufficiently free of other materials such that any impurities do not materially affect the biological properties of the protein or cause other adverse consequences. That is, a nucleic acid or peptide of this disclosure is purified if it is substantially free of cellular material, viral material, or culture medium when produced by recombinant DNA techniques, or chemical precursors or other chemicals when chemically synthesized. Purity and 20 homogeneity are typically determined using analytical chemistry techniques, for example, polyacrylamide gel electrophoresis or high-performance liquid chromatography. The term "purified" can denote that a nucleic acid or protein gives rise to essentially one band in an electrophoretic gel. For a protein that can be subjected to modifications, for example, phosphorylation or glycosylation, different modifications may give rise to different isolated 25 proteins, which can be separately purified. By "isolated polynucleotide" is meant a nucleic acid (e.g., a DNA) that is free of the genes which, in the naturally-occurring genome of the organism from which the nucleic acid molecule of the disclosure is derived, flank the gene. The term therefore includes, for example, a recombinant DNA that is incorporated into a vector; into an autonomously 30 replicating plasmid or virus; or into the genomic DNA of a prokaryote or eukaryote; or that exists as a separate molecule (for example, a cDNA or a genomic or cDNA fragment produced by PCR or restriction endonuclease digestion) independent of other sequences. In addition, the term includes an RNA molecule that is transcribed from a DNA molecule, as 2020216484   17 Mar 2026 well as a recombinant DNA that is part of a hybrid gene encoding additional polypeptide sequence. By an "isolated polypeptide" is meant a polypeptide of the disclosure that has been separated from components that naturally accompany it. Typically, the polypeptide is 5 isolated when it is at least 60%, by weight, free from the proteins and naturally-occurring organic molecules with which it is naturally associated. Preferably, the preparation is at least 75%, more preferably at least 90%, and most preferably at least 99%, by weight, a polypeptide of the disclosure. An isolated polypeptide of the disclosure may be obtained, for example, by extraction from a natural source, by expression of a recombinant nucleic acid 10 encoding such a polypeptide; or by chemically synthesizing the protein. Purity can be measured by any appropriate method, for example, column chromatography, polyacrylamide gel electrophoresis, or by HPLC analysis. The term “linker,” as used herein, can refer to a covalent linker (e.g., covalent bond), a non-covalent linker, a chemical group, or a molecule linking two molecules or moieties, 15   e.g., two components of a protein complex or a ribonucleocomplex, or two domains of a fusion protein, such as, for example, a polynucleotide programmable DNA binding domain (e.g., dCas9) and one or more deaminase domains (e.g., an adenosine deaminase and / or a cytidine deaminase). A linker can join different components of, or different portions of components of, a base editor system. For example, in some embodiments, a linker can join a 20 guide polynucleotide binding domain of a polynucleotide programmable nucleotide binding domain and a catalytic domain of a deaminase. In some embodiments, a linker can join a CRISPR polypeptide and a deaminase. In some embodiments, a linker can join a Cas9 and a deaminase. In some embodiments, a linker can join a dCas9 and a deaminase. In some embodiments, a linker can join a nCas9 and a deaminase. In some embodiments, a linker can 25 join a guide polynucleotide and a deaminase. In some embodiments, a linker can join a deaminating component and a polynucleotide programmable nucleotide binding component of a base editor system. In some embodiments, a linker can join a RNA-binding portion of a deaminating component and a polynucleotide programmable nucleotide binding component of a base editor system. In some embodiments, a linker can join a RNA-binding portion of a 30 deaminating component and a RNA-binding portion of a polynucleotide programmable nucleotide binding component of a base editor system. A linker can be positioned between, or flanked by, two groups, molecules, or other moieties and connected to each one via a covalent bond or non-covalent interaction, thus connecting the two. In some embodiments, 2020216484   17 Mar 2026 the linker can be an organic molecule, group, polymer, or chemical moiety. In some embodiments, the linker can be a polynucleotide. In some embodiments, the linker can be a DNA linker. In some embodiments, the linker can be a RNA linker. In some embodiments, a linker can comprise an aptamer capable of binding to a ligand. In some embodiments, the 5 ligand may be carbohydrate, a peptide, a protein, or a nucleic acid. In some embodiments, the linker may comprise an aptamer may be derived from a riboswitch. The riboswitch from which the aptamer is derived may be selected from a theophylline riboswitch, a thiamine pyrophosphate (TPP) riboswitch, an adenosine cobalamin (AdoCbl) riboswitch, an S-adenosyl methionine (SAM) riboswitch, an SAH riboswitch, a flavin mononucleotide (FMN) 10 riboswitch, a tetrahydrofolate riboswitch, a lysine riboswitch, a glycine riboswitch, a purine riboswitch, a GlmS riboswitch, or a pre-queosine1 (PreQ1) riboswitch. In some embodiments, a linker may comprise an aptamer bound to a polypeptide or a protein domain, such as a polypeptide ligand. In some embodiments, the polypeptide ligand may be a K Homology (KH) domain, a MS2 coat protein domain, a PP7 coat protein domain, a SfMu 15 Com coat protein domain, a sterile alpha motif, a telomerase Ku binding motif and Ku protein, a telomerase Sm7 binding motif and Sm7 protein, or a RNA recognition motif. In some embodiments, the polypeptide ligand may be a portion of a base editor system component. For example, a nucleobase editing component may comprise one or more deaminase domains and a RNA recognition motif. 20          In some embodiments, the linker can be an amino acid or a plurality of amino acids (e.g., a peptide or protein). In some embodiments, the linker can be about 5-100 amino acids in length, for example, about 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 20-30, 3040, 40-50, 50-60, 60-70, 70-80, 80-90, or 90-100 amino acids in length. In some embodiments, the linker can be about 100-150, 150-200, 200-250, 250-300, 300-350, 350 25   400, 400-450, or 450-500 amino acids in length. Longer or shorter linkers can be also contemplated. In some embodiments, a linker joins a gRNA binding domain of an RNA-programmable nuclease, including a Cas9 nuclease domain, and the catalytic domain of a nucleic-acid editing protein (e.g., cytidine and / or adenosine deaminase). In some 30 embodiments, a linker joins a dCas9 and a nucleic-acid editing protein. For example, the linker is positioned between, or flanked by, two groups, molecules, or other moieties and connected to each one via a covalent bond, thus connecting the two. In some embodiments, the linker is an amino acid or a plurality of amino acids (e.g., a peptide or protein). In some 2020216484   17 Mar 2026 embodiments, the linker is an organic molecule, group, polymer, or chemical moiety. In some embodiments, the linker is 5-200 amino acids in length, for example, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 35, 45, 50, 55, 60, 60, 65, 70, 70, 75, 80, 85, 90, 90, 95, 100, 101, 102, 103, 104, 105, 110, 120, 130, 140, 150, 160, 175, 180, 190, or 200 amino 5 acids in length. Longer or shorter linkers are also contemplated. In some embodiments, the domains of the nucleobase editor (e.g., multi-effector nucleobase editor) are fused via a linker that comprises the amino acid sequence of SGGSSGSETPGTSESATPESSGGS, SGGSSGGSSGSETPGTSESATPESSGGSSGGS, or GGSGGSPGSPAGSPTSTEEGTSESATPESGPGTSTEPSEGSAPGSPAGSPTSTEEGTSTE 10  PSEGSAPGTSTEPSEGSAPGTSESATPESGPGSEPATSGGSGGS. In some embodiments, domains of the nucleobase editor (e.g., multi-effector nucleobase editor) are fused via a linker comprising the amino acid sequence SGSETPGTSESATPES, which may also be referred to as the XTEN linker. In some embodiments, a linker comprises the amino acid sequence SGGS. In some embodiments, a linker comprises (SGGS)n, (GGGS)n, (GGGGS) n, (G)n, 15   (EAAAK)n, (GGS)n, SGSETPGTSESATPES, or (XP)n motif, or a combination of any of these, wherein n is independently an integer between 1 and 30, and wherein X is any amino acid. In some embodiments, n is 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, or 15. In some embodiments, the linker is 24 amino acids in length. In some embodiments, the linker comprises the amino acid sequence SGGSSGGSSGSETPGTSESATPES. In some 20 embodiments, the linker is 40 amino acids in length. In some embodiments, the linker comprises the amino acid sequence SGGSSGGSSGSETPGTSESATPESSGGSSGGSSGGSSGGS. In some embodiments, the linker is 64 amino acids in length. In some embodiments, the linker comprises the amino acid sequence 25 SGGSSGGSSGSETPGTSESATPESSGGSSGGSSGGSSGGSSGSETPGTSESATPESSGGS SGGS. In some embodiments, the linker is 92 amino acids in length. In some embodiments, the linker comprises the amino acid sequence PGSPAGSPTSTEEGTSESATPESGPGTSTEPSEGSAPGSPAGSPTSTEEGTSTEPSEGSAPG TSTEPSEGSAPGTSESATPESGPGSEPATS. 30          By “marker” is meant any protein or polynucleotide having an alteration in expression level or activity that is associated with a disease or disorder. The term “mutation,” as used herein, refers to a substitution of a residue within a sequence, e.g., a nucleic acid or amino acid sequence, with another residue, or a deletion or 2020216484   17 Mar 2026 insertion of one or more residues within a sequence. Mutations are typically described herein by identifying the original residue followed by the position of the residue within the sequence and by the identity of the newly substituted residue. Various methods for making the amino acid substitutions (mutations) provided herein are well known in the art, and are provided by, 5 for example, Green and Sambrook, Molecular Cloning: A Laboratory Manual (4th ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. (2012)). In some embodiments, the presently disclosed base editors can efficiently generate an “intended mutation,” such as a point mutation, in a nucleic acid (e.g., a nucleic acid within a genome of a subject) without generating a significant number of unintended mutations, such as unintended point mutations. 10 In some embodiments, an intended mutation is a mutation that is generated by a specific base editor (e.g., cytidine base editor and / or adenosine base editor) bound to a guide polynucleotide (e.g., gRNA), specifically designed to generate the intended mutation. In general, mutations made or identified in a sequence (e.g., an amino acid sequence as described herein) are numbered in relation to a reference (or wild-type) sequence, i.e., a 15 sequence that does not contain the mutations. The skilled practitioner in the art would readily understand how to determine the position of mutations in amino acid and nucleic acid sequences relative to a reference sequence. The term “non-conservative mutations” involve amino acid substitutions between different groups, for example, lysine for tryptophan, or phenylalanine for serine, etc. In this 20 case, it is preferable for the non-conservative amino acid substitution to not interfere with, or inhibit the biological activity of, the functional variant. The non-conservative amino acid substitution can enhance the biological activity of the functional variant, such that the biological activity of the functional variant is increased as compared to the wild-type protein. The term “nuclear localization sequence,” “nuclear localization signal,” or “NLS” 25 refers to an amino acid sequence that promotes import of a protein into the cell nucleus. Nuclear localization sequences are known in the art and described, for example, in Plank et al., International PCT application, PCT / EP2000 / 011690, filed November 23, 2000, published as WO / 2001 / 038547 on May 31, 2001, the contents of which are incorporated herein by reference for their disclosure of exemplary nuclear localization sequences. In other 30 embodiments, the NLS is an optimized NLS described, for example, by Koblan et al., Nature Biotech. 2018 doi:10.1038 / nbt.4172. In some embodiments, an NLS comprises the amino acid sequence KRTADGSEFESPKKKRKV, KRPAATKKAGQAKKKK, 2020216484   17 Mar 2026 KKTELQTTNAENKTKKL, KRGINDRNFWRGENGRKTR, RKSGKIAAIVVKRPRK, PKKKRKV, or MDSLLMNRRKFLYQFKNVRWAKGRRETYLC. The terms “nucleic acid” and “nucleic acid molecule,” as used herein, refer to a compound comprising a nucleobase and an acidic moiety, e.g., a nucleoside, a nucleotide, or 5 a polymer of nucleotides. Typically, polymeric nucleic acids, e.g., nucleic acid molecules comprising three or more nucleotides are linear molecules, in which adjacent nucleotides are linked to each other via a phosphodiester linkage. In some embodiments, “nucleic acid” refers to individual nucleic acid residues (e.g. nucleotides and / or nucleosides). In some embodiments, “nucleic acid” refers to an oligonucleotide chain comprising three or more 10 individual nucleotide residues. As used herein, the terms “oligonucleotide” and “polynucleotide” can be used interchangeably to refer to a polymer of nucleotides (e.g., a string of at least three nucleotides). In some embodiments, “nucleic acid” encompasses RNA as well as single and / or double-stranded DNA. Nucleic acids may be naturally occurring, for example, in the context of a genome, a transcript, an mRNA, tRNA, rRNA, siRNA, snRNA, 15 a plasmid, cosmid, chromosome, chromatid, or other naturally occurring nucleic acid molecule. On the other hand, a nucleic acid molecule may be a non-naturally occurring molecule, e.g., a recombinant DNA or RNA, an artificial chromosome, an engineered genome, or fragment thereof, or a synthetic DNA, RNA, DNA / RNA hybrid, or including non-naturally occurring nucleotides or nucleosides. Furthermore, the terms “nucleic acid,” 20 “DNA,” “RNA,” and / or similar terms include nucleic acid analogs, e.g., analogs having other than a phosphodiester backbone. Nucleic acids can be purified from natural sources, produced using recombinant expression systems and optionally purified, chemically synthesized, etc. Where appropriate, e.g., in the case of chemically synthesized molecules, nucleic acids can comprise nucleoside analogs such as analogs having chemically modified 25 bases or sugars, and backbone modifications. A nucleic acid sequence is presented in the 5’ to 3' direction unless otherwise indicated. In some embodiments, a nucleic acid is or comprises natural nucleosides (e.g. adenosine, thymidine, guanosine, cytidine, uridine, deoxyadenosine, deoxythymidine, deoxyguanosine, and deoxycytidine); nucleoside analogs (e.g., 2-aminoadenosine, 2-thiothymidine, inosine, pyrrolo-pyrimidine, 3-methyl adenosine, 30 5-methylcytidine, 2-aminoadenosine, C5-bromouridine, C5-fluorouridine, C5-iodouridine, C5-propynyl-uridine, C5-propynyl-cytidine, C5-methylcytidine, 2-aminoadenosine, 7-deazaadenosine, 7-deazaguanosine, 8-oxoadenosine, 8-oxoguanosine, O(6)-methylguanine, and 2-thiocytidine); chemically modified bases; biologically modified bases (e.g., methylated 2020216484   17 Mar 2026 bases); intercalated bases; modified sugars ( 2‘-e.g., fluororibose, ribose, 2'-deoxyribose, arabinose, and hexose); and / or modified phosphate groups (e.g., phosphorothioates and 5‘-N-phosphoramidite linkages). The term "nucleic acid programmable DNA binding protein" or "napDNAbp" may be 5 used interchangeably with “polynucleotide programmable nucleotide binding domain” to refer to a protein that associates with a nucleic acid (e.g., DNA or RNA), such as a guide nucleic acid or guide polynucleotide (e.g., gRNA), that guides the napDNAbp to a specific nucleic acid sequence. In some embodiments, the polynucleotide programmable nucleotide binding domain is a polynucleotide programmable DNA binding domain. In some 10 embodiments, the polynucleotide programmable nucleotide binding domain is a polynucleotide programmable RNA binding domain. In some embodiments, the polynucleotide programmable nucleotide binding domain is a Cas9 protein. A Cas9 protein can associate with a guide RNA that guides the Cas9 protein to a specific DNA sequence that is complementary to the guide RNA. In some embodiments, the napDNAbp is a Cas9 15 domain, for example a nuclease active Cas9, a Cas9 nickase (nCas9), or a nuclease inactive Cas9 (dCas9). Non-limiting examples of nucleic acid programmable DNA binding proteins include, Cas9 (e.g., dCas9 and nCas9), Cas12a / Cpfl, Cas12b / C2cl, Cas12c / C2c3, Cas12d / CasY, Cas12e / CasX, Cas12g, Cas12h, and Cas12i. Non-limiting examples of Cas enzymes include Cas1, Cas1B, Cas2, Cas3, Cas4, Cas5, Cas5d, Cas5t, Cas5h, Cas5a, Cas6, 20 Cas7, Cas8, Cas8a, Cas8b, Cas8c, Cas9 (also known as Csn1 or Csx12), Cas10, Cas10d, Cas12a / Cpfl, Cas12b / C2cl, Cas12c / C2c3, Cas12d / CasY, Cas12e / CasX, Cas12g, Cas12h, Cas12i, Csy1 , Csy2, Csy3, Csy4, Cse1, Cse2, Cse3, Cse4, Cse5e, Csc1, Csc2, Csa5, Csn1, Csn2, Csm1, Csm2, Csm3, Csm4, Csm5, Csm6, Cmr1, Cmr3, Cmr4, Cmr5, Cmr6, Csb1, Csb2, Csb3, Csx17, Csx14, Csx10, Csx16, CsaX, Csx3, Csx1, Csx1S, Csx11, Csf1, Csf2, 25 CsO, Csf4, Csd1, Csd2, Cst1, Cst2, Csh1, Csh2, Csa1, Csa2, Csa3, Csa4, Csa5, Type II Cas effector proteins, Type V Cas effector proteins, Type VI Cas effector proteins, CARF, DinG, homologues thereof, or modified or engineered versions thereof. Other nucleic acid programmable DNA binding proteins are also within the scope of this disclosure, although they may not be specifically listed in this disclosure. See, e.g., Makarova et al. 30 “Classification and Nomenclature of CRISPR-Cas Systems: Where from Here?” CRISPR J. 2018 Oct;1:325-336. doi: 10.1089 / crispr.2018.0033; Yan et al., “Functionally diverse type V CRISPR-Cas systems” Science. 2019 Jan 4;363(6422):88-91. doi: 10.1126 / science.aav7271, the entire contents of each are hereby incorporated by reference. 2020216484   17 Mar 2026 The term “nucleobase,” “nitrogenous base,” or “base,” used interchangeably herein, refers to a nitrogen-containing biological compound that forms a nucleoside, which in turn is a component of a nucleotide. The ability of nucleobases to form base pairs and to stack one upon another leads directly to long-chain helical structures such as ribonucleic acid (RNA) 5 and deoxyribonucleic acid (DNA). Five nucleobases - adenine (A), cytosine (C), guanine (G), thymine (T), and uracil (U) - are called primary or canonical. Adenine and guanine are derived from purine, and cytosine, uracil, and thymine are derived from pyrimidine. DNA and RNA can also contain other (non-primary) bases that are modified. Non-limiting exemplary modified nucleobases can include hypoxanthine, xanthine, 7-methylguanine, 5,6 10 dihydrouracil, 5-methylcytosine (m5C), and 5-hydromethylcytosine. Hypoxanthine and xanthine can be created through mutagen presence, both of them through deamination (replacement of the amine group with a carbonyl group). Hypoxanthine can be modified from adenine. Xanthine can be modified from guanine. Uracil can result from deamination of cytosine. A “nucleoside” consists of a nucleobase and a five carbon sugar (either ribose or 15 deoxyribose). Examples of a nucleoside include adenosine, guanosine, uridine, cytidine, 5-methyluridine (m5U), deoxyadenosine, deoxyguanosine, thymidine, deoxyuridine, and deoxycytidine. Examples of a nucleoside with a modified nucleobase includes inosine (I), xanthosine (X), 7-methylguanosine (m7G), dihydrouridine (D), 5-methylcytidine (m5C), and pseudouridine (T). A “nucleotide” consists of a nucleobase, a five carbon sugar (either 20 ribose or deoxyribose), and at least one phosphate group. The terms “nucleobase editing domain” or “nucleobase editing protein,” as used herein, refers to a protein or enzyme that can catalyze a nucleobase modification in RNA or DNA, such as cytosine (or cytidine) to uracil (or uridine) or thymine (or thymidine), and adenine (or adenosine) to hypoxanthine (or inosine) deaminations, as well as non-templated 25 nucleotide additions and insertions. In some embodiments, the nucleobase editing domain is a deaminase domain (e.g., an adenine deaminase or an adenosine deaminase; or a cytidine deaminase or a cytosine deaminase). In some embodiments, the nucleobase editing domain is more than one deaminase domain (e.g., an adenine deaminase or an adenosine deaminase and a cytidine or a cytosine deaminase). In some embodiments, the nucleobase editing domain 30 can be a naturally occurring nucleobase editing domain. In some embodiments, the nucleobase editing domain can be an engineered or evolved nucleobase editing domain from the naturally occurring nucleobase editing domain. The nucleobase editing domain can be 2020216484   17 Mar 2026 from any organism, such as a bacterium, human, chimpanzee, gorilla, monkey, cow, dog, rat, or mouse. As used herein, “obtaining” as in “obtaining an agent” includes synthesizing, purchasing, or otherwise acquiring the agent. 5          A “patient” or “subject” as used herein refers to a mammalian subject or individual diagnosed with, at risk of having or developing, or suspected of having or developing a disease or a disorder. In some embodiments, the term “patient” refers to a mammalian subject with a higher than average likelihood of developing a disease or a disorder. Exemplary patients can be humans, non-human primates, cats, dogs, pigs, cattle, cats, horses, 10 camels, llamas, goats, sheep, rodents (e.g., mice, rabbits, rats, or guinea pigs) and other mammalians that can benefit from the therapies disclosed herein. Exemplary human patients can be male and / or female. “Patient in need thereof” or “subject in need thereof” is referred to herein as a patient diagnosed with, at risk or having, predetermined to have, or suspected of having a disease or 15 disorder. The terms “pathogenic mutation,” “pathogenic variant,” “disease casing mutation,” “disease causing variant,” “deleterious mutation,” or “predisposing mutation” refers to a genetic alteration or mutation that increases an individual’s susceptibility or predisposition to a certain disease or disorder. In some embodiments, the pathogenic mutation comprises at 20 least one wild-type amino acid substituted by at least one pathogenic amino acid in a protein encoded by a gene. The term “pharmaceutically-acceptable carrier” means a pharmaceutically-acceptable material, composition or vehicle, such as a liquid or solid filler, diluent, excipient, manufacturing aid (e.g., lubricant, talc magnesium, calcium or zinc stearate, or steric acid), or 25 solvent encapsulating material, involved in carrying or transporting the compound from one site (e.g., the delivery site) of the body, to another site (e.g., organ, tissue or portion of the body). A pharmaceutically acceptable carrier is “acceptable” in the sense of being compatible with the other ingredients of the formulation and not injurious to the tissue of the subject (e.g., physiologically compatible, sterile, physiologic pH, etc.). The terms such as 30 “excipient,” “carrier,” “pharmaceutically acceptable carrier,” “vehicle,” or the like are used interchangeably herein. The term “pharmaceutical composition” means a composition formulated for pharmaceutical use. 2020216484   17 Mar 2026 The terms “protein,” “peptide,” “polypeptide,” and their grammatical equivalents are used interchangeably herein, and refer to a polymer of amino acid residues linked together by peptide (amide) bonds. The terms refer to a protein, peptide, or polypeptide of any size, structure, or function. Typically, a protein, peptide, or polypeptide will be at least three 5 amino acids long. A protein, peptide, or polypeptide can refer to an individual protein or a collection of proteins. One or more of the amino acids in a protein, peptide, or polypeptide can be modified, for example, by the addition of a chemical entity such as a carbohydrate group, a hydroxyl group, a phosphate group, a farnesyl group, an isofarnesyl group, a fatty acid group, a linker for conjugation, functionalization, or other modifications, etc. A protein, 10 peptide, or polypeptide can also be a single molecule or can be a multi-molecular complex. A protein, peptide, or polypeptide can be just a fragment of a naturally occurring protein or peptide. A protein, peptide, or polypeptide can be naturally occurring, recombinant, or synthetic, or any combination thereof. The term “fusion protein” as used herein refers to a hybrid polypeptide which comprises protein domains from at least two different proteins. 15 One protein can be located at the amino-terminal (N-terminal) portion of the fusion protein or at the carboxy-terminal (C-terminal) protein thus forming an amino-terminal fusion protein or a carboxy-terminal fusion protein, respectively. A protein can comprise different domains, for example, a nucleic acid binding domain (e.g., the gRNA binding domain of Cas9 that directs the binding of the protein to a target site) and a nucleic acid cleavage domain, or a 20 catalytic domain of a nucleic acid editing protein. In some embodiments, a protein comprises a proteinaceous part, e.g., an amino acid sequence constituting a nucleic acid binding domain, and an organic compound, e.g., a compound that can act as a nucleic acid cleavage agent. In some embodiments, a protein is in a complex with, or is in association with, a nucleic acid, e.g., RNA or DNA. Any of the proteins provided herein can be produced by any method 25 known in the art. For example, the proteins provided herein can be produced via recombinant protein expression and purification, which is especially suited for fusion proteins comprising a peptide linker. Methods for recombinant protein expression and purification are well known, and include those described by Green and Sambrook, Molecular Cloning: A Laboratory Manual (4th ed., Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y. 30   (2012)), the entire contents of which are incorporated herein by reference. Polypeptides and proteins disclosed herein (including functional portions and functional variants thereof) can comprise synthetic amino acids in place of one or more naturally-occurring amino acids. Such synthetic amino acids are known in the art, and 2020216484   17 Mar 2026 include, for example, aminocyclohexane carboxylic acid, norleucine, a-amino n-decanoic acid, homoserine, S-acetylaminomethyl-cysteine, trans-3- and trans-4-hydroxyproline, 4-aminophenylalanine, 4-nitrophenylalanine, 4-chlorophenylalanine, 4-carboxyphenylalanine, P-phenylserine P-hydroxyphenylalanine, phenylglycine, a-naphthylalanine, 5 cyclohexylalanine, cyclohexylglycine, indoline-2-carboxylic acid, 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid, aminomalonic acid, aminomalonic acid monoamide, N’-benzyl-N’-methyl-lysine, N’,N’-dibenzyl-lysine, 6-hydroxylysine, ornithine, a-aminocyclopentane carboxylic acid, a-aminocyclohexane carboxylic acid, a-aminocycloheptane carboxylic acid, a-(2-amino-2-norbornane)-carboxylic acid, a,Y- 10 diaminobutyric acid, a,P-diaminopropionic acid, homophenylalanine, and a-tert-butylglycine. The polypeptides and proteins can be associated with post-translational modifications of one or more amino acids of the polypeptide constructs. Non-limiting examples of post-translational modifications include phosphorylation, acylation including acetylation and formylation, glycosylation (including N-linked and O-linked), amidation, hydroxylation, 15 alkylation including methylation and ethylation, ubiquitylation, addition of pyrrolidone carboxylic acid, formation of disulfide bridges, sulfation, myristoylation, palmitoylation, isoprenylation, farnesylation, geranylation, glypiation, lipoylation and iodination. The term "recombinant" as used herein in the context of proteins or nucleic acids refers to proteins or nucleic acids that do not occur in nature, but are the product of human 20 engineering. For example, in some embodiments, a recombinant protein or nucleic acid molecule comprises an amino acid or nucleotide sequence that comprises at least one, at least two, at least three, at least four, at least five, at least six, or at least seven mutations as compared to any naturally occurring sequence. By “reduces” is meant a negative alteration of at least 10%, 25%, 50%, 75%, or 25   100%. By “reference” is meant a standard or control condition. In one embodiment, the reference is a wild-type or healthy cell. In other embodiments and without limitation, a reference is an untreated cell that is not subjected to a test condition, or is subjected to placebo or normal saline, medium, buffer, and / or a control vector that does not harbor a 30 polynucleotide of interest. A “reference sequence” is a defined sequence used as a basis for sequence comparison. A reference sequence may be a subset of or the entirety of a specified sequence; for example, a segment of a full-length cDNA or gene sequence, or the complete cDNA or 2020216484   17 Mar 2026 gene sequence. For polypeptides, the length of the reference polypeptide sequence will generally be at least about 16 amino acids, at least about 20 amino acids, at least about 25 amino acids, about 35 amino acids, about 50 amino acids, or about 100 amino acids. For nucleic acids, the length of the reference nucleic acid sequence will generally be at least 5 about 50 nucleotides, at least about 60 nucleotides, at least about 75 nucleotides, about 100 nucleotides or about 300 nucleotides or any integer thereabout or therebetween. In some embodiments, a reference sequence is a wild-type sequence of a protein of interest. In other embodiments, a reference sequence is a polynucleotide sequence encoding a wild-type protein. 10         The term "RNA-programmable nuclease," and "RNA-guided nuclease" are used with (e.g., binds or associates with) one or more RNA(s) that is not a target for cleavage. In some embodiments, an RNA-programmable nuclease, when in a complex with an RNA, may be referred to as a nuclease:RNA complex. Typically, the bound RNA(s) is referred to as a guide RNA (gRNA). 15           In some embodiments, the RNA-programmable nuclease is the (CRISPR-associated system) Cas9 endonuclease, for example, Cas9 (Casnl) from Streptococcus pyogenes (see, e.g., "Complete genome sequence of an Ml strain of Streptococcus pyogenes." Ferretti J.J., et al., Proc. Natl. Acad. Sci. U.S.A. 98:4658-4663(2001); "CRISPR RNA maturation by transencoded small RNA and host factor RNase III." Deltcheva E., et al., Nature 471:602 20   607(2011). Because RNA-programmable nucleases (e.g., Cas9) use RNA:DNA hybridization to target DNA cleavage sites, these proteins are able to be targeted, in principle, to any sequence specified by the guide RNA. Methods of using RNA-programmable nucleases, such as Cas9, for site-specific cleavage (e.g., to modify a genome) are known in the art (see e.g., Cong, L. et 25 al., Multiplex genome engineering using CRISPR / Cas systems. Science 339, 819-823 (2013); Mali, P. et al., RNA-guided human genome engineering via Cas9. Science 339, 823-826 (2013); Hwang, W.Y. et al., Efficient genome editing in zebrafish using a CRISPR-Cas system. Nature biotechnology 31, 227-229 (2013); Jinek, M. et ah, RNA-programmed genome editing in human cells. eLife 2, e00471 (2013); Dicarlo, J.E. et al., Genome engineering in 30 Saccharomyces cerevisiae using CRISPR-Cas systems. Nucleic acids research (2013); Jiang, W. et al., RNA-guided editing of bacterial genomes using CRISPR-Cas systems. Nature biotechnology 31, 233-239 (2013); the entire contents of each of which are incorporated herein by reference). 2020216484   17 Mar 2026 The term “single nucleotide polymorphism (SNP)” is a variation in a single nucleotide that occurs at a specific position in the genome, where each variation is present to some appreciable degree within a population (e.g., > 1%). For example, at a specific base position in the human genome, the C nucleotide can appear in most individuals, but in a minority of 5 individuals, the position is occupied by an A. This means that there is a SNP at this specific position, and the two possible nucleotide variations, C or A, are said to be alleles for this position. SNPs underlie differences in susceptibility to disease. The severity of illness and the way our body responds to treatments are also manifestations of genetic variations. SNPs can fall within coding regions of genes, non-coding regions of genes, or in the intergenic 10 regions (regions between genes). In some embodiments, SNPs within a coding sequence do not necessarily change the amino acid sequence of the protein that is produced, due to degeneracy of the genetic code. SNPs in the coding region are of two types: synonymous and nonsynonymous SNPs. Synonymous SNPs do not affect the protein sequence, while nonsynonymous SNPs change the amino acid sequence of protein. The nonsynonymous 15 SNPs are of two types: missense and nonsense. SNPs that are not in protein-coding regions can still affect gene splicing, transcription factor binding, messenger RNA degradation, or the sequence of noncoding RNA. Gene expression affected by this type of SNP is referred to as an eSNP (expression SNP) and can be upstream or downstream from the gene. A single nucleotide variant (SNV) is a variation in a single nucleotide without any limitations of 20 frequency and can arise in somatic cells. A somatic single nucleotide variation can also be called a single-nucleotide alteration. By "specifically binds" is meant a nucleic acid molecule, polypeptide, or complex thereof (e.g., a nucleic acid programmable DNA binding domain and guide nucleic acid), compound, or molecule that recognizes and binds a polypeptide and / or nucleic acid molecule 25 of the disclosure, but which does not substantially recognize and bind other molecules in a sample, for example, a biological sample. Nucleic acid molecules useful in the methods of the present disclosure include any nucleic acid molecule that encodes a polypeptide of this disclosure or a fragment thereof. Such nucleic acid molecules need not be 100% identical with an endogenous nucleic acid 30 sequence, but will typically exhibit substantial identity. Polynucleotides having “substantial identity” to an endogenous sequence are typically capable of hybridizing with at least one strand of a double-stranded nucleic acid molecule. Nucleic acid molecules useful in the methods of the present disclosure include any nucleic acid molecule that encodes a 2020216484   17 Mar 2026 polypeptide of this disclosure or a fragment thereof. Such nucleic acid molecules need not be 100% identical with an endogenous nucleic acid sequence, but will typically exhibit substantial identity. Polynucleotides having “substantial identity” to an endogenous sequence are typically capable of hybridizing with at least one strand of a double-stranded nucleic acid 5 molecule. By "hybridize" is meant pair to form a double-stranded molecule between complementary polynucleotide sequences (e.g., a gene described herein), or portions thereof, under various conditions of stringency. (See, e.g., Wahl, G. M. and S. L. Berger (1987) Methods Enzymol. 152:399; Kimmel, A. R. (1987) Methods Enzymol. 152:507). For example, stringent salt concentration will ordinarily be less than about 750 mM 10 NaCl and 75 mM trisodium citrate, preferably less than about 500 mM NaCl and 50 mM trisodium citrate, and more preferably less than about 250 mM NaCl and 25 mM trisodium citrate. Low stringency hybridization can be obtained in the absence of organic solvent, e.g., formamide, while high stringency hybridization can be obtained in the presence of at least about 35% formamide, and more preferably at least about 50% formamide. Stringent 15 temperature conditions will ordinarily include temperatures of at least about 30° C, more preferably of at least about 37° C, and most preferably of at least about 42° C. Varying additional parameters, such as hybridization time, the concentration of detergent, e.g., sodium dodecyl sulfate (SDS), and the inclusion or exclusion of carrier DNA, are well known to those skilled in the art. Various levels of stringency are accomplished by combining these 20 various conditions as needed. In a one: embodiment, hybridization will occur at 30° C in 750 mM NaCl, 75 mM trisodium citrate, and 1% SDS. In another embodiment, hybridization will occur at 37° C in 500 mM NaCl, 50 mM trisodium citrate, 1% SDS, 35% formamide, and 100 ug ml denatured salmon sperm DNA (ssDNA). In another embodiment, hybridization will occur at 42° C in 250 mM NaCl, 25 mM trisodium citrate, 1% SDS, 50% formamide, 25 and 200 gg / ml ssDNA. Useful variations on these conditions will be readily apparent to those skilled in the art. For most applications, washing steps that follow hybridization will also vary in stringency. Wash stringency conditions can be defined by salt concentration and by temperature. As above, wash stringency can be increased by decreasing salt concentration or 30 by increasing temperature. For example, stringent salt concentration for the wash steps will preferably be less than about 30 mM NaCl and 3 mM trisodium citrate, and most preferably less than about 15 mM NaCl and 1.5 mM trisodium citrate. Stringent temperature conditions for the wash steps will ordinarily include a temperature of at least about 25° C, more 2020216484   17 Mar 2026 preferably of at least about 42° C, and even more preferably of at least about 68° C. In an embodiment, wash steps will occur at 25° C in 30 mM NaCl, 3 mM trisodium citrate, and 0.1% SDS. In a more preferred embodiment, wash steps will occur at 42 C in 15 mM NaCl, 1.5 mM trisodium citrate, and 0.1% SDS. In a more preferred embodiment, wash steps will 5 occur at 68° C in 15 mM NaCl, 1.5 mM trisodium citrate, and 0.1% SDS. Additional variations on these conditions will be readily apparent to those skilled in the art. Hybridization techniques are well known to those skilled in the art and are described, for example, in Benton and Davis (Science 196:180, 1977); Grunstein and Hogness (Proc. Natl. Acad. Sci., USA 72:3961, 1975); Ausubel et al. (Current Protocols in Molecular Biology, 10 Wiley Interscience, New York, 2001); Berger and Kimmel (Guide to Molecular Cloning Techniques, 1987, Academic Press, New York); and Sambrook et al., Molecular Cloning: A Laboratory Manual, Cold Spring Harbor Laboratory Press, New York. By “split” is meant divided into two or more fragments. A "split Cas9 protein" or "split Cas9" refers to a Cas9 protein that is provided as an N-15 terminal fragment and a C-terminal fragment encoded by two separate nucleotide sequences. The polypeptides corresponding to the N-terminal portion and the C-terminal portion of the Cas9 protein may be spliced to form a “reconstituted” Cas9 protein. In particular embodiments, the Cas9 protein is divided into two fragments within a disordered region of the protein, e.g., as described in Nishimasu et al., Cell, Volume 156, Issue 5, pp. 935-949, 20   2014, or as described in Jiang et al. (2016) Science 351: 867-871. PDB file: 5F9R, each of which is incorporated herein by reference. In some embodiments, the protein is divided into two fragments at any C, T, A, or S within a region of SpCas9 between about amino acids A292-G364, F445-K483, or E565-T637, or at corresponding positions in any other Cas9, Cas9 variant (e.g., nCas9, dCas9), or other napDNAbp. In some embodiments, protein is 25 divided into two fragments at SpCas9 T310, T313, A456, S469, or C574. In some embodiments, the process of dividing the protein into two fragments is referred to as “splitting” the protein. In other embodiments, the N-terminal portion of the Cas9 protein comprises amino acids 1-573 or 1-637 S. pyogenes Cas9 wild-type (SpCas9) (NCBI Reference Sequence: 30   NC_002737.2, Uniprot Reference Sequence: Q99ZW2) and the C-terminal portion of the Cas9 protein comprises a portion of amino acids 574-1368 or 638-1368 of SpCas9 wild-type. The C-terminal portion of the split Cas9 can be joined with the N-terminal portion of the split Cas9 to form a complete Cas9 protein. In some embodiments, the C-terminal portion 2020216484   17 Mar 2026 of the Cas9 protein starts from where the N-terminal portion of the Cas9 protein ends. As such, in some embodiments, the C-terminal portion of the split Cas9 comprises a portion of amino acids (551-651)-1368 of spCas9. "(551-651)-1368" means starting at an amino acid between amino acids 551-651 (inclusive) and ending at amino acid 1368. For example, the C-5 terminal portion of the split Cas9 may comprise a portion of any one of amino acid 551-1368, 552-1368, 553-1368, 554-1368, 555-1368, 556-1368, 557-1368, 558-1368, 559-1368, 5601368, 561-1368, 562-1368, 563-1368, 564-1368, 565-1368, 566-1368, 567-1368, 568-1368, 569-1368, 570-1368, 571-1368, 572-1368, 573-1368, 574-1368, 575-1368, 576-1368, 5771368, 578-1368, 579-1368, 580-1368, 581-1368, 582-1368, 583-1368, 584-1368, 585-1368, 10   586-1368, 587-1368, 588-1368, 589-1368, 590-1368, 591-1368, 592-1368, 593-1368, 594 1368, 595-1368, 596-1368, 597-1368, 598-1368, 599-1368, 600-1368, 601-1368, 602-1368, 603-1368, 604-1368, 605-1368, 606-1368, 607-1368, 608-1368, 609-1368, 610-1368, 6111368, 612-1368, 613-1368, 614-1368, 615-1368, 616-1368, 617-1368, 618-1368, 619-1368, 620-1368, 621-1368, 622-1368, 623-1368, 624-1368, 625-1368, 626-1368, 627-1368, 62815   1368, 629-1368, 630-1368, 631-1368, 632-1368, 633-1368, 634-1368, 635-1368, 636-1368, 637-1368, 638-1368, 639-1368, 640-1368, 641-1368, 642-1368, 643-1368, 644-1368, 6451368, 646-1368, 647-1368, 648-1368, 649-1368, 650-1368, or 651-1368 of spCas9. In some embodiments, the C-terminal portion of the split Cas9 protein comprises a portion of amino acids 574-1368 or 638-1368 of SpCas9. 20          By "subject" is meant a mammal, including, but not limited to, a human or non human mammal, such as a bovine, equine, canine, ovine, or feline. Subjects include livestock, domesticated animals raised to produce labor and to provide commodities, such as food, including without limitation, cattle, goats, chickens, horses, pigs, rabbits, and sheep. By "substantially identical" is meant a polypeptide or nucleic acid molecule 25 exhibiting at least 50% identity to a reference amino acid sequence (for example, any one of the amino acid sequences described herein) or nucleic acid sequence (for example, any one of the nucleic acid sequences described herein). In one embodiment, such a sequence is at least 60%, 80% or 85%, 90%, 95% or even 99% identical at the amino acid level or nucleic acid to the sequence used for comparison. 30          Sequence identity is typically measured using sequence analysis software (for example, Sequence Analysis Software Package of the Genetics Computer Group, University of Wisconsin Biotechnology Center, 1710 University Avenue, Madison, Wis. 53705, BLAST, BESTFIT, GAP, or PILEUP / PRETTYBOX programs). Such software matches 2020216484   17 Mar 2026 identical or similar sequences by assigning degrees of homology to various substitutions, deletions, and / or other modifications. Conservative substitutions typically include substitutions within the following groups: glycine, alanine; valine, isoleucine, leucine; aspartic acid, glutamic acid, asparagine, glutamine; serine, threonine; lysine, arginine; and 5 phenylalanine, tyrosine. In an exemplary approach to determining the degree of identity, a BLAST program may be used, with a probability score between e-3 and e-100 indicating a closely related sequence. COBALT is used, for example, with the following parameters: 10 a) alignment parameters: Gap penalties-11,-1 and End-Gap penalties-5,-1, b) CDD Parameters: Use RPS BLAST on; Blast E-value 0.003; Find Conserved columns and Recompute on, and c) Query Clustering Parameters: Use query clusters on; Word Size 4; Max cluster distance 0.8; Alphabet Regular. EMBOSS Needle is used, for example, with the following parameters: 15 20 a) b) c) d) e) f) g) Matrix: BLOSUM62; GAP OPEN: 10; GAP EXTEND: 0.5; OUTPUT FORMAT: pair; END GAP PENALTY: false; END GAP OPEN: 10; and END GAP EXTEND: 0.5. The term "target site" refers to a sequence within a nucleic acid molecule that is modified by a nucleobase editor. In one embodiment, the target site is deaminated by a deaminase or a fusion protein comprising a deaminase (e.g., cytidine or adenine deaminase). 25           As used herein, the terms “treat,” treating,” “treatment,” and the like refer to reducing or ameliorating a disorder and / or symptoms associated therewith or obtaining a desired pharmacologic and / or physiologic effect. It will be appreciated that, although not precluded, treating a disorder or condition does not require that the disorder, condition or symptoms associated therewith be completely eliminated. In some embodiments, the effect is 30 therapeutic, i.e., without limitation, the effect partially or completely reduces, diminishes, abrogates, abates, alleviates, decreases the intensity of, or cures a disease and / or adverse symptom attributable to the disease. In some embodiments, the effect is preventative, i.e., the effect protects or prevents an occurrence or reoccurrence of a disease or condition. To this 2020216484   17 Mar 2026 end, the presently disclosed methods comprise administering a therapeutically effective amount of a compositions as described herein. By “uracil glycosylase inhibitor” or “UGI” is meant an agent that inhibits the uracil-excision repair system. In one embodiment, the agent is a protein or fragment thereof that 5 binds a host uracil-DNA glycosylase and prevents removal of uracil residues from DNA. In an embodiment, a UGI is a protein, a fragment thereof, or a domain that is capable of inhibiting a uracil-DNA glycosylase base-excision repair enzyme. In some embodiments, a UGI domain comprises a wild-type UGI or a modified version thereof. In some embodiments, a UGI domain comprises a fragment of the exemplary amino acid sequence set 10 forth below. In some embodiments, a UGI fragment comprises an amino acid sequence that comprises at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or 100% of the exemplary UGI sequence provided below. In some embodiments, a UGI comprises an amino acid sequence that is homologous to the exemplary UGI amino acid sequence or fragment 15 thereof, as set forth below. In some embodiments, the UGI, or a portion thereof, is at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, at least 96%, at least 97%, at least 98%, at least 99%, at least 99.5%, at least 99.9%, or 100% identical to a wildtype UGI or a UGI sequence, or portion thereof, as set forth below. An exemplary UGI comprises an amino acid sequence as follows: 20 >splP14739IUNGI_BPPB2 Uracil-DNA glycosylase inhibitor MTNLSDIIEKETGKQLVIQESILMLPEEVEEVIGNKPESDILVHTAYDESTDENVMLLTSD APEYKPWALVIQDSNGENKIKML. The term “vector” refers to a means of introducing a nucleic acid sequence into a cell, resulting in a transformed cell. Vectors include plasmids, transposons, phages, viruses, 25 liposomes, and episome. “Expression vectors” are nucleic acid sequences comprising the nucleotide sequence to be expressed in the recipient cell. Expression vectors may include additional nucleic acid sequences to promote and / or facilitate the expression of the of the introduced sequence such as start, stop, enhancer, promoter, and secretion sequences. Any compositions or methods provided herein can be combined with one or more of 30 any of the other compositions and methods provided herein. DNA editing has emerged as a viable means to modify disease states by correcting pathogenic mutations at the genetic level. Until recently, all DNA editing platforms have functioned by inducing a DNA double strand break (DSB) at a specified genomic site and 2020216484   17 Mar 2026 relying on endogenous DNA repair pathways to determine the product outcome in a semistochastic manner, resulting in complex populations of genetic products. Though precise, user-defined repair outcomes can be achieved through the homology directed repair (HDR) pathway, a number of challenges have prevented high efficiency repair using HDR in 5 therapeutically-relevant cell types. In practice, this pathway is inefficient relative to the competing, error-prone non-homologous end joining pathway. Further, HDR is tightly restricted to the G1 and S phases of the cell cycle, preventing precise repair of DSBs in postmitotic cells. As a result, it has proven difficult or impossible to alter genomic sequences in a user-defined, programmable manner with high efficiencies in these populations. 10                BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A-1C depict cis-trans activity of free deaminases. FIG. 1A are schematics depicting an experimental design of a cis-trans assay for SpCas9 and deaminases in a base editor complex or untethered format. FIG. 1B is a graph depicting cis-trans activity of rAPOBEC. FIG. 1C is a graph depicting cis-trans activity of TadA7.10 and TadA- 15   TadA7.10. FIGS. 2A-2F depict a cis-trans assay for base editors, an illustration of a deaminase similarity network and screening of 153 deaminases. FIG. 2A is a schematic depicting an experimental design of a cis-trans assay. Separate plasmids encoding SaCas9, gRNA for SaCas9 and target base editors were used to transfect HEK293T cells. FIG. 2B is a 20 schematic depicting a similarity network of APOBEC-like deaminases. Dots represent cytidine deaminases screened as next-generation CBEs and indicate core next-generation CBEs. The shade of the dots represent average in trans / in cis ratio; the size of the dots represent average in cis activity. Methods of creating the similarity network of cytidine deaminases shown in FIG. 2B are as follows: To focus the search space within the 25 APOBEC1-like protein family, human APOBEC1 was used as a query sequence for a protein BLAST search against the NCBI non-redundant protein sequences database (nr_v5). The top 1000 sequences were used to generate a sequence similarity network (SSN) with a protein BLAST -log(E-value) edge-threshold of 115. A set of 43 deaminases was selected to sample the sequence space within the SSN. To identify deaminases from other families that could 30 act as base-editing enzymes, 80 sequences from a SSN built from all deaminases was sampled with the following InterPro annotations IPR002125 (Cytidine and deoxycytidylate deaminase domain), IPR016192 (APOBEC / CMP deaminase, zinc-binding), and IPR016193 (Cytidine deaminase-like). This set of 82,043 sequences was first clustered at 55% identity 2020216484   17 Mar 2026 using Cd-HIT3 before generating a SSN network by protein BLAST with a -log(E-value) edge-threshold of 50. Sequences were chosen based on their centrality within a cluster of sequence in the network. FIG. 2C is a graph depicting cis-trans activity of ppBE4 and its mutants. FIG. 2D is a graph depicting cis-trans activity of selected editors. Separately, cis- 5 trans-activity data was generated based on in cis / in trans assay on three target sites, site 1, site 4, and site 6, as shown in FIG. 2E and FIG. 2F. FIG. 2E presents a bar graph showing in cis and in trans editing activity of identified CBEs. Shown is a comparison of in cis and in trans editing frequencies of mammalian cells treated with candidate CBEs. Editor numbers 1-36 are base editors pYY-BEM3.8, pYY-BEM3.9, pYY-BEM3.10, pYY-BEM3.11, pYY- 10  BEM3.12, pYY-BEM3.13, pYY-BEM3.14, pYY-BEM3.15, pYY-BEM3.16, pYY- BEM3.17, pYY-BEM3.18, pYY-BEM3.19, pYY-BEM3.20, pYY-BEM3.21, pYY-BEM3.22, pYY-BEM3.23, pYY-BEM3.24, pYY-BEM3.25, pYY-BEM3.26, pYY-BEM3.27, pYY-BEM3.28, pYY-BEM3.29, pYY-BEM3.30, pYY-BEM3.31, pYY-BEM3.32, pYY-BEM3.33, pYY-BEM3.34, pYY-BEM3.35, pYY-BEM3.36, pYY- 15  BEM3.37, pYY-BEM3.38, pYY-BEM3.39, pYY-BEM3.40, pYY-BEM3.41, pYY- BEM3.42, pYY-BEM3.43, respectively. Base editing efficiencies were reported for the most edited base in the target sites. FIG. 2F presents a bar graph showing in cis and in trans editing activity of identified CBEs. Shown is a comparison of in cis and in trans editing frequencies of mammalian cells treated with candidate CBEs. Editor numbers 1-37 are 20 rBE4max, mAPOBEC-1, MaAPOBEC-1, hAPOBEC-1, ppAPOBEC-1, OcAPOBEC1, MdAPOBEC-1, mAPOBEC-2, hAPOBEC-2, ppAPOBEC-2, BtAPOBEC-2, mAPOBEC-3, hAPOBEC-3A, hAPOBEC-3B, hAPOBEC-3C, hAPOBEC-3D, hAPOBEC-3F, hAPOBEC-3G, hAPOBEC-4, mAPOBEC-4, rAPOBEC-4, MfAPOBEC-4, hAID, negative control, btAID, mAID, pmCDA-1, pmCDA-2, pmCDA-5, yCD, pYY-BEM3.1, pYY-BEM3.2, pYY- 25   BEM3.3, pYY-BEM3.4, pYY-BEM3.5, pYY-BEM3.6, pYY-BEM3.7, respectively. Base editing efficiencies were reported for the most edited base in the target sites. FIGS. 3A and 3B depict cis-trans activity. FIG. 3A is a graph depicting cis-trans activity of ABE7.10. FIG. 3B is a graph depicting cis-trans activity of BE4max. FIGS. 4A and 4B depict rAPOBEC1 homology models generated by SWISSMODEL 30 using hAPOBEC3C structure (PDB ID 3VM8). ssDNA from hAPOBEC3A structure (PDB ID 5SWW) is manually docked. FIG. 4A is a schematic depicting mutations that potentially affect ssDNA binding. FIG. 4B is a schematic depicting mutations that potentially affect catalytic activity. 2020216484   17 Mar 2026 FIGS. 5A-5C depict cis-trans activity of rAPOBEC1 mutants. FIGS. 6A-6E depict cis-trans activity of rAPOBEC1 double mutants. FIG. 6A are graphs depicting in cis and in trans activity of rAPOBEC1 double mutants. FIG. 6B is a graph depicting in cis activities at 6 sites. FIG. 6C is a graph depicting cis / trans ratio. FIG. 5 6D is a graph depicting in cis activities at 6 sites. FIG. 6E is a graph depicting cis / trans ratio. FIGS. 7A and 7B depict cis-trans activity of deaminases in first round of screening. FIGS. 8A-8C are graphs depicting on target activity of ppAPOBEC1 versus rAPOBEC1. 10          FIG. 9 is a schematic depicting a similarity network of APOBEC-like proteins. FIGS. 10A and 10B are graphs depicting dose dependency studies on in cis activity and in trans activity in TadA-TadA7.10 and rAPOBEC1, respectively. FIG. 11 is a graph depicting off-target editing of selected CBEs. SNVs were identified by exome sequencing. 15          FIGS. 12A and 12B are graphs depicting quantification of base editor mRNA and protein, respectfully, from HEK293T cells transfected with base editor plasmids. FIG. 13 is a graph depicting targeted RNA sequencing for selected editors. Three regions of 200-300 bp were sequenced. FIG. 14 is a graph depicting guided off-target editing of selected CBEs. 20          FIGS. 15A-15E depict editing windows of selected editors. FIG. 16 is a graph depicting indel rate of selected CBEs at 10 target sites. FIGS. 17A-17D show pictorial illustrations and graphs related to unguided ssDNA deamination and in cis / in trans assay. FIG. 17A illustrates potential ssDNA formation in the genome during transcription or translation. FIG. 17B illustrates an experimental design of in 25 cis / in trans assay. Separate constructs encoding SaCas9, gRNA for SaCas9 and base editor were used to transfect HEK293T cells. in cis and in trans activity was measured in different transfections but at the target site with NGGRRT PAM sequence. FIG. 17C shows in cis / in trans activities of BE4 with rAPOBEC1. FIG. 17D shows ABE7.10 variant at 34 genomic sites. The leftmost bars at each of the genomic sites on the x-axis indicate in cis, on target 30 editing. The rightmost bars at each of the genomic sites on the x-axis indicate in trans editing. Base editing efficiencies were reported for the most-edited base in the target sites. Values and error bars reflect the mean and standard deviation (s.d.) of independent biological duplicates. 2020216484   17 Mar 2026 FIG. 18 presents a bar graph showing identified next generation CBEs with high in cis activities and reduced in trans activities compared to BE4 with rAPOBEC1. Shown is a comparison of in cis and in trans editing frequencies of mammalian cells treated with next generation CBEs (BE4 with PpAPOBEC1[wt, H122], RrA3F [wt, F130L], AmAPOBEC1, 5 SsAPOBEC2[wt, R54Q] at 10 genomic sites. Base editing efficiencies were reported for the most edited base in the target sites. Values and error bars reflect the mean and s.d. of 4 independent biological replicates. FIGS. 19A-19E show allele frequencies and graphs related to next-generation CBEs with reduced DNA and RNA off-target editing relative to BE4 in mammalian cells. FIG. 10   19A shows whole transcriptome sequencing and target RNA sequencing (FIG. 19B) of Hek293T cells expressing spurious deamination minimized cytosine base editors. FIG. 19C shows the percentage of C to T editing at known guided off-target sites. FIG. 19D shows the percentage of C to T editing in in vitro enzymatic assay on single strand DNA substrates. C to U editing of core next-generation CBEs on ssDNA substrates. Dots represent NC local 15 sequence context of edit. Black line indicates average editing efficiency across target cytosines in substrates. FIG. 29E presents a time course of product formation in in vitro enzymatic assay from cell lysates containing selected CBEs. The sequences of the oligos used in FIGS. 19D and 19E are listed in the table presented in Example 5 infra. Values and error bars reflect the mean and s.d. of independent biological triplicates (FIGS. 19A, B, C) or 20 duplicates (FIGS. 19D, E). FIG. 20 graphically depicts in cis / in trans editing activities of BE4 with rAPOBEC1 mutants shown in FIGS. 4A and 4B at site 1. Base editing efficiencies were reported for the most edited base in the target sites. In trans efficiency is indicated by the leftmost for each target site on the x-axis; in cis efficiency is indicated by the right bars for each target sit on 25 the x-axis. Values and error bars reflect the mean and s.d. of independent biological duplicates. FIG. 21 depicts in cis / in trans editing activities of BE4-rAPOBEC1 with HiFi mutations at 10 target sites. Values and error bars reflect the mean and s.d. of four independent biological replicates. 30          FIGS. 22A and 22B show a graph and sequence alignments related to in cis / in trans editing activities and sequence alignment of CBEs tested in the 1st round screening. in cis / in trans editing activities at site 10 (FIG. 22A) and sequence alignment (FIG. 22B) of selected 2020216484   17 Mar 2026 CBEs. The amino acid residues that align to HiFi mutations in rAPOBEC1 are highlighted. Values and error bars reflect the mean and s.d. of independent biological duplicates. FIG. 23 demonstrates the in cis / in trans activities of BE4-PpAPOBEC1 and BE4-PpAPOBEC with HiFi mutations at 10 target sites. Base editing efficiencies were reported 5 for the most edited base in the target sites. Values and error bars reflect the mean and s.d. of four independent biological replicates. FIG. 24 shows a heatmap indicating prior base preference of CBEs shown in FIG. 18B. Values used to generate the heatmap reflect the mean of four independent biological duplicates. 10          FIG. 25 presents an editing window of CBEs shown in FIG. 18B at 10 target sites. Values reflect the mean of four independent biological replicates. In cis and in trans editing are presented in the leftmost and rightmost panel heatmaps, respectively. FIG. 26 presents a table showing indel rates of CBEs shown in FIG. 18B at 10 target sites. Values used to generate the heatmap reflect the mean of four independent biological 15 duplicates. FIGS. 27A-27D depict homology models of four cytidine deaminases selected based on existing crystal structures. FIG. 27A: Homology model of PpAPOBEC1 is based on based on a putative APOBEC3G structure (PDB ID 5K81). FIG. 27B: RrA3F is based on Vif-binding Domain of hAPOBEC3F (PDB ID 3WUS). FIG. 27C: AmAPOBEC1 is based 20 on a hAPOBEC3B N-terminal domain (PDB ID 5TKM). FIG. 27D: SsAPOBEC2 is based on Vif-binding Domain of hAPOBEC3F (PDB ID 3WUS). FIGS. 28A-28D present graphs illustrating guided off-target editing of selected next generation CBEs. FIG. 28A: Editing efficiency of next generation CBEs on HEK2, HEK3, HEK4 sites, and FIG. 28B: reported guided off-target sites for HEK2 sgRNA, c, HEK3 25 sgRNA and FIG. 28D: HEK4 sgRNA. Base editing efficiencies were reported for the most-edited base in the target sites. Values and error bars reflect the mean and s.d. of independent biological triplicates. FIG. 29 presents a graph showing C to T editing efficiency of selected CBEs on ssDNA substrates in in vitro enzymatic assay. The editing efficiencies were measured at all 30   25 cytidines in 2 ssDNA substrates, and grouped by NC sequence context. Sequences of the two substrates used are listed in Table 18 herein. Values and error bars reflect the mean and s.d. of data obtained from independent biological duplicates. 2020216484   17 Mar 2026 FIG. 30 presents a graph showing quantification of CBE protein concentration in HEK293T cells transfected with base editor expression plasmids. Base editor protein concentration was quantified by measuring the total Cas9 protein concentration and the amount of total protein in a cell lysate. BE protein concentration was normalized to BE4- 5 rAPOBEC1. Values and error bars reflect the mean and s.d. of two or more independent biological replicates. FIG. 31 presents a graph showing spurious deamination activity of CBEs examined by whole genome sequencing (WGS). Relative mutation rates are shown in odds-ratio. DETAILED DESCRIPTION 10          The disclosure provides nucleobase editors and multi-effector nucleobase editors having an improved editing profile with minimal off-target deamination, compositions comprising such editors, and methods of using the same to generate modifications in target nucleobase sequences. NUCLEOBASE EDITORS 15          Disclosed herein is a base editor or a nucleobase editor or multi-effector nucleobase editors for editing, modifying or altering a target nucleotide sequence of a polynucleotide. Described herein is a nucleobase editor or a base editor or multi-effector nucleobase editor comprising a polynucleotide programmable nucleotide binding domain (e.g., Cas9) and at least one nucleobase editing domain (e.g., adenosine deaminase and / or cytidine deaminase). 20 A polynucleotide programmable nucleotide binding domain (e.g., Cas9), when in conjunction with a bound guide polynucleotide (e.g., gRNA), can specifically bind to a target polynucleotide sequence (i.e., via complementary base pairing between bases of the bound guide nucleic acid and bases of the target polynucleotide sequence) and thereby localize the base editor to the target nucleic acid sequence desired to be edited. 25 Polynucleotide Programmable Nucleotide Binding Domain It should be appreciated that polynucleotide programmable nucleotide binding domains can also include nucleic acid programmable proteins that bind RNA. For example, the polynucleotide programmable nucleotide binding domain can be associated with a nucleic acid that guides the polynucleotide programmable nucleotide binding domain to an RNA. 30 Other nucleic acid programmable DNA binding proteins are also within the scope of this disclosure, though they are not specifically listed in this disclosure. 2020216484   17 Mar 2026 A polynucleotide programmable nucleotide binding domain of a base editor can itself comprise one or more domains. For example, a polynucleotide programmable nucleotide binding domain can comprise one or more nuclease domains. In some embodiments, the nuclease domain of a polynucleotide programmable nucleotide binding domain can comprise 5 an endonuclease or an exonuclease. Herein the term “exonuclease” refers to a protein or polypeptide capable of digesting a nucleic acid (e.g., RNA or DNA) from free ends, and the term “endonuclease” refers to a protein or polypeptide capable of catalyzing (e.g., cleaving) internal regions in a nucleic acid (e.g., DNA or RNA). In some embodiments, an endonuclease can cleave a single strand of a double-stranded nucleic acid. In some 10 embodiments, an endonuclease can cleave both strands of a double-stranded nucleic acid molecule. In some embodiments a polynucleotide programmable nucleotide binding domain can be a deoxyribonuclease. In some embodiments a polynucleotide programmable nucleotide binding domain can be a ribonuclease. In some embodiments, a nuclease domain of a polynucleotide programmable 15 nucleotide binding domain can cut zero, one, or two strands of a target polynucleotide. In some embodiments, the polynucleotide programmable nucleotide binding domain can comprise a nickase domain. Herein the term “nickase” refers to a polynucleotide programmable nucleotide binding domain comprising a nuclease domain that is capable of cleaving only one strand of the two strands in a duplexed nucleic acid molecule (e.g., DNA). 20 In some embodiments, a nickase can be derived from a fully catalytically active (e.g., natural) form of a polynucleotide programmable nucleotide binding domain by introducing one or more mutations into the active polynucleotide programmable nucleotide binding domain. For example, where a polynucleotide programmable nucleotide binding domain comprises a nickase domain derived from Cas9, the Cas9-derived nickase domain can include a D10A 25 mutation and a histidine at position 840. In such embodiments, the residue H840 retains catalytic activity and can thereby cleave a single strand of the nucleic acid duplex. In another example, a Cas9-derived nickase domain can comprise an H840A mutation, while the amino acid residue at position 10 remains a D. In some embodiments, a nickase can be derived from a fully catalytically active (e.g., natural) form of a polynucleotide programmable 30 nucleotide binding domain by removing all or a portion of a nuclease domain that is not required for the nickase activity. For example, where a polynucleotide programmable nucleotide binding domain comprises a nickase domain derived from Cas9, the Cas9-derived 2020216484   17 Mar 2026 nickase domain can comprise a deletion of all or a portion of the RuvC domain or the HNH domain. The amino acid sequence of an exemplary catalytically active Cas9 is as follows: MDKKYSIGLDIGTNSVGWAVITDEYKVPSKKFKVLGNTDRHSIKKNLIGALLFDSGETAEAT 5 RLKRTARRRYTRRKNRICYLQEIFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFGNIVD EVAYHEKYPTIYHLRKKLVDSTDKADLRLIYLALAHMIKFRGHFLIEGDLNPDNSDVDKLFI QLVQTYNQLFEENPINASGVDAKAILSARLSKSRRLENLIAQLPGEKKNGLFGNLIALSLGL TPNFKSNFDLAEDAKLQLSKDTYDDDLDNLLAQIGDQYADLFLAAKNLSDAILLSDILRVNT EITKAPLSASMIKRYDEHHQDLTLLKALVRQQLPEKYKEIFFDQSKNGYAGYIDGGASQEEF 10 YKFIKPILEKMDGTEELLVKLNREDLLRKQRTFDNGSIPHQIHLGELHAILRRQEDFYPFLK DNREKIEKILTFRIPYYVGPLARGNSRFAWMTRKSEETITPWNFEEVVDKGASAQSFIERMT NFDKNLPNEKVLPKHSLLYEYFTVYNELTKVKYVTEGMRKPAFLSGEQKKAIVDLLFKTNRK VTVKQLKEDYFKKIECFDSVEISGVEDRFNASLGTYHDLLKIIKDKDFLDNEENEDILEDIV LTLTLFEDREMIEERLKTYAHLFDDKVMKQLKRRRYTGWGRLSRKLINGIRDKQSGKTILDF 15 LKSDGFANRNFMQLIHDDSLTFKEDIQKAQVSGQGDSLHEHIANLAGSPAIKKGILQTVKVV DELVKVMGRHKPENIVIEMARENQTTQKGQKNSRERMKRIEEGIKELGSQILKEHPVENTQL QNEKLYLYYLQNGRDMYVDQELDINRLSDYDVDHIVPQSFLKDDSIDNKVLTRSDKNRGKSD NVPSEEVVKKMKNYWRQLLNAKLITQRKFDNLTKAERGGLSELDKAGFIKRQLVETRQITKH VAQILDSRMNTKYDENDKLIREVKVITLKSKLVSDFRKDFQFYKVREINNYHHAHDAYLNAV 20 VGTALIKKYPKLESEFVYGDYKVYDVRKMIAKSEQEIGKATAKYFFYSNIMNFFKTEITLAN GEIRKRPLIETNGETGEIVWDKGRDFATVRKVLSMPQVNIVKKTEVQTGGFSKESILPKRNS DKLIARKKDWDPKKYGGFDSPTVAYSVLVVAKVEKGKSKKLKSVKELLGITIMERSSFEKNP IDFLEAKGYKEVKKDLIIKLPKYSLFELENGRKRMLASAGELQKGNELALPSKYVNFLYLAS HYEKLKGSPEDNEQKQLFVEQHKHYLDEIIEQISEFSKRVILADANLDKVLSAYNKHRDKPI 25 REQAENIIHLFTLTNLGAPAAFKYFDTTIDRKRYTSTKEVLDATLIHQSITGLYETRIDLSQ LGGD. A base editor comprising a polynucleotide programmable nucleotide binding domain comprising a nickase domain is thus able to generate a single-strand DNA break (nick) at a specific polynucleotide target sequence (e.g., determined by the complementary sequence of 30 a bound guide nucleic acid). In some embodiments, the strand of a nucleic acid duplex target polynucleotide sequence that is cleaved by a base editor comprising a nickase domain (e.g., Cas9-derived nickase domain) is the strand that is not edited by the base editor (i.e., the strand that is cleaved by the base editor is opposite to a strand comprising a base to be edited). In other embodiments, a base editor comprising a nickase domain (e.g., Cas9- 2020216484   17 Mar 2026 derived nickase domain) can cleave the strand of a DNA molecule which is being targeted for editing. In such embodiments, the non-targeted strand is not cleaved. Also provided herein are base editors comprising a polynucleotide programmable nucleotide binding domain which is catalytically dead (i.e., incapable of cleaving a target 5 polynucleotide sequence). Herein the terms “catalytically dead” and “nuclease dead” are used interchangeably to refer to a polynucleotide programmable nucleotide binding domain which has one or more mutations and / or deletions resulting in its inability to cleave a strand of a nucleic acid. In some embodiments, a catalytically dead polynucleotide programmable nucleotide binding domain base editor can lack nuclease activity as a result of specific point 10 mutations in one or more nuclease domains. For example, in the case of a base editor comprising a Cas9 domain, the Cas9 can comprise both a D10A mutation and an H840A mutation. Such mutations inactivate both nuclease domains, thereby resulting in the loss of nuclease activity. In other embodiments, a catalytically dead polynucleotide programmable nucleotide binding domain can comprise one or more deletions of all or a portion of a 15   catalytic domain (e.g., RuvC1 and / or HNH domains). In further embodiments, a catalytically dead polynucleotide programmable nucleotide binding domain comprises a point mutation (e.g., D10A or H840A) as well as a deletion of all or a portion of a nuclease domain. Also contemplated herein are mutations capable of generating a catalytically dead polynucleotide programmable nucleotide binding domain from a previously functional 20 version of the polynucleotide programmable nucleotide binding domain. For example, in the case of catalytically dead Cas9 (“dCas9”), variants having mutations other than D10A and H840A are provided, which result in nuclease inactivated Cas9. Such mutations, by way of example, include other amino acid substitutions at D10 and H840, or other substitutions within the nuclease domains of Cas9 (e.g., substitutions in the HNH nuclease subdomain 25 and / or the RuvC1 subdomain). Additional suitable nuclease-inactive dCas9 domains can be apparent to those of skill in the art based on this disclosure and knowledge in the field, and are within the scope of this disclosure. Such additional exemplary suitable nuclease-inactive Cas9 domains include, but are not limited to, D10A / H840A, D10A / D839A / H840A, and D10A / D839A / H840A / N863A mutant domains (See, e.g., Prashant et al., CAS9 30 transcriptional activators for target specificity screening and paired nickases for cooperative genome engineering. Nature Biotechnology. 2013; 31(9): 833-838, the entire contents of which are incorporated herein by reference). 2020216484   17 Mar 2026 Non-limiting examples of a polynucleotide programmable nucleotide binding domain which can be incorporated into a base editor include a CRISPR protein-derived domain, a restriction nuclease, a meganuclease, TAL nuclease (TALEN), and a zinc finger nuclease (ZFN). In some embodiments, a base editor comprises a polynucleotide programmable 5 nucleotide binding domain comprising a natural or modified protein or portion thereof which via a bound guide nucleic acid is capable of binding to a nucleic acid sequence during CRISPR (i.e., Clustered Regularly Interspaced Short Palindromic Repeats)-mediated modification of a nucleic acid. Such a protein is referred to herein as a “CRISPR protein.” Accordingly, disclosed herein is a base editor comprising a polynucleotide programmable 10 nucleotide binding domain comprising all or a portion of a CRISPR protein (i.e. a base editor comprising as a domain all or a portion of a CRISPR protein, also referred to as a “CRISPR protein-derived domain” of the base editor). A CRISPR protein-derived domain incorporated into a base editor can be modified compared to a wild-type or natural version of the CRISPR protein. For example, as described below a CRISPR protein-derived domain can comprise 15 one or more mutations, insertions, deletions, rearrangements and / or recombinations relative to a wild-type or natural version of the CRISPR protein. CRISPR is an adaptive immune system that provides protection against mobile genetic elements (viruses, transposable elements and conjugative plasmids). CRISPR clusters contain spacers, sequences complementary to antecedent mobile elements, and target 20 invading nucleic acids. CRISPR clusters are transcribed and processed into CRISPR RNA (crRNA). In type II CRISPR systems, correct processing of pre-crRNA requires a transencoded small RNA (tracrRNA), endogenous ribonuclease 3 (rnc) and a Cas9 protein. The tracrRNA serves as a guide for ribonuclease 3-aided processing of pre-crRNA. Subsequently, Cas9 / crRNA / tracrRNA endonucleolytically cleaves linear or circular dsDNA 25 target complementary to the spacer. The target strand not complementary to crRNA is first cut endonucleolytically, and then trimmed 3‘-5‘ exonucleolytically. In nature, DNA-binding and cleavage typically requires protein and both RNAs. However, single guide RNAs (“sgRNA,” or simply “gNRA”) can be engineered so as to incorporate aspects of both the crRNA and tracrRNA into a single RNA species. See, e.g., Jinek M., et al., Science 337:816 30   821(2012), the entire contents of which is hereby incorporated by reference. Cas9 recognizes a short motif in the CRISPR repeat sequences (the PAM or protospacer adjacent motif) to help distinguish self versus non-self. 2020216484   17 Mar 2026 In some embodiments, the methods described herein can utilize an engineered Cas protein. A guide RNA (gRNA) is a short synthetic RNA composed of a scaffold sequence necessary for Cas-binding and a user-defined ~20 nucleotide spacer that defines the genomic target to be modified. Thus, a skilled artisan can change the genomic target of the Cas 5 protein specificity is partially determined by how specific the gRNA targeting sequence is for the genomic target compared to the rest of the genome. In some embodiments, the gRNA scaffold sequence is as follows: GUUUUAGAGC UAGAAAUAGC AAGUUAAAAU AAGGCUAGUC CGUUAUCAAC UUGAAAAAGU GGCACCGAGU CGGUGCUUUU. 10          In some embodiments, a CRISPR protein-derived domain incorporated into a base editor is an endonuclease (e.g., deoxyribonuclease or ribonuclease) capable of binding a target polynucleotide when in conjunction with a bound guide nucleic acid. In some embodiments, a CRISPR protein-derived domain incorporated into a base editor is a nickase capable of binding a target polynucleotide when in conjunction with a bound guide nucleic 15 acid. In some embodiments, a CRISPR protein-derived domain incorporated into a base editor is a catalytically dead domain capable of binding a target polynucleotide when in conjunction with a bound guide nucleic acid. In some embodiments, a target polynucleotide bound by a CRISPR protein derived domain of a base editor is DNA. In some embodiments, a target polynucleotide bound by a CRISPR protein-derived domain of a base editor is RNA. 20          Cas proteins that can be used herein include class 1 and class 2. Non-limiting examples of Cas proteins include Cas1, Cas1B, Cas2, Cas3, Cas4, Cas5, Cas5d, Cas5t, Cas5h, Cas5a, Cas6, Cas7, Cas8, Cas9 (also known as Csn1 or Csx12), Cas10, Csy1 , Csy2, Csy3, Csy4, Cse1, Cse2, Cse3, Cse4, Cse5e, Csc1, Csc2, Csa5, Csn1, Csn2, Csm1, Csm2, Csm3, Csm4, Csm5, Csm6, Cmr1, Cmr3, Cmr4, Cmr5, Cmr6, Csb1, Csb2, Csb3, Csx17, 25 Csx14, Csx10, Csx16, CsaX, Csx3, Csx1, Csx1S, Csf1, Csf2, CsO, Csf4, Csd1, Csd2, Cst1, Cst2, Csh1, Csh2, Csa1, Csa2, Csa3, Csa4, Csa5, Cas12a / Cpf1, Cas12b / C2c1, Cas12c / C2c3, Cas12d / CasY, Cas12e / CasX, Cas12g, Cas12h, and Cas12i, CARF, DinG, homologues thereof, or modified versions thereof. An unmodified CRISPR enzyme can have DNA cleavage activity, such as Cas9, which has two functional endonuclease domains: RuvC and 30 HNH. A CRISPR enzyme can direct cleavage of one or both strands at a target sequence, such as within a target sequence and / or within a complement of a target sequence. For example, a CRISPR enzyme can direct cleavage of one or both strands within about 1, 2, 3, 4, 2020216484   17 Mar 2026 5, 6, 7, 8, 9, 10, 15, 20, 25, 50, 100, 200, 500, or more base pairs from the first or last nucleotide of a target sequence. A vector that encodes a CRISPR enzyme that is mutated to with respect, to a corresponding wild-type enzyme such that the mutated CRISPR enzyme lacks the ability to 5 cleave one or both strands of a target polynucleotide containing a target sequence can be used. Cas9 can refer to a polypeptide with at least or at least about 50%, 60%, 70%, 80%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity and / or sequence homology to a wild-type exemplary Cas9 polypeptide (e.g., Cas9 from S. pyogenes). Cas9 can refer to a polypeptide with at most or at most about 50%, 60%, 70%, 10   80%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity and / or sequence homology to a wild-type exemplary Cas9 polypeptide (e.g., from S. pyogenes). Cas9 can refer to the wild-type or a modified form of the Cas9 protein that can comprise an amino acid change such as a deletion, insertion, substitution, variant, mutation, fusion, chimera, or any combination thereof. 15          In some embodiments, a CRISPR protein-derived domain of a base editor can include all or a portion of Cas9 from Corynebacterium ulcerans (NCBI Refs: NC_015683.1, NC_017317.1); Corynebacterium diphtheria (NCBI Refs: NC_016782.1, NC_016786.1); Spiroplasma syrphidicola (NCBI Ref: NC_021284.1); Prevotella intermedia (NCBI Ref: NC_017861.1); Spiroplasma taiwanense (NCBI Ref: NC_021846.1); Streptococcus iniae 20 (NCBI Ref: NC_021314.1); Belliella baltica (NCBI Ref: NC_018010.1); Psychroflexus torquis (NCBI Ref: NC_018721.1); Streptococcus thermophilus (NCBI Ref: YP_820832.1); Listeria innocua (NCBI Ref: NP_472073.1); Campylobacter jejuni (NCBI Ref: YP_002344900.1); Neisseria meningitidis (NCBI Ref: YP_002342100.1), Streptococcus pyogenes, or Staphylococcus aureus. 25 Cas9 domains of Nucleobase Editors Cas9 nuclease sequences and structures are well known to those of skill in the art (See, e.g., “Complete genome sequence of an Ml strain of Streptococcus pyogenes.” Ferretti et al., Proc. Natl. Acad. Sci. U.S.A. 98:4658-4663(2001); “CRISPR RNA maturation by trans-encoded small RNA and host factor RNase III.” Deltcheva E., et al., Nature 471:602 30   607(2011); and “A programmable dual-RNA-guided DNA endonuclease in adaptive bacterial immunity.” Jinek M., et al., Science 337:816-821(2012), the entire contents of each of which are incorporated herein by reference). Cas9 orthologs have been described in various species, including, but not limited to, S. pyogenes and S. thermophilus. Additional suitable Cas9 2020216484   17 Mar 2026 nucleases and sequences will be apparent to those of skill in the art based on this disclosure, and such Cas9 nucleases and sequences include Cas9 sequences from the organisms and loci disclosed in Chylinski, Rhun, and Charpentier, “The tracrRNA and Cas9 families of type II CRISPR-Cas immunity systems” (2013) RNA Biology 10:5, 726-737; the entire contents of 5 which are incorporated herein by reference. In some embodiments, a nucleic acid programmable DNA binding protein (napDNAbp) is a Cas9 domain. Non-limiting, exemplary Cas9 domains are provided herein. The Cas9 domain may be a nuclease active Cas9 domain, a nuclease inactive Cas9 domain (dCas9), or a Cas9 nickase (nCas9). In some embodiments, the Cas9 domain is a nuclease 10 active domain. For example, the Cas9 domain may be a Cas9 domain that cuts both strands of a duplexed nucleic acid (e.g., both strands of a duplexed DNA molecule). In some embodiments, the Cas9 domain comprises any one of the amino acid sequences as set forth herein. In some embodiments the Cas9 domain comprises an amino acid sequence that is at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at 15 least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to any one of the amino acid sequences set forth herein. In some embodiments, the Cas9 domain comprises an amino acid sequence that has 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 21, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 or more or more mutations compared to any one of 20 the amino acid sequences set forth herein. In some embodiments, the Cas9 domain comprises an amino acid sequence that has at least 10, at least 15, at least 20, at least 30, at least 40, at least 50, at least 60, at least 70, at least 80, at least 90, at least 100, at least 150, at least 200, at least 250, at least 300, at least 350, at least 400, at least 500, at least 600, at least 700, at least 800, at least 900, at least 1000, at least 1100, or at least 1200 identical contiguous amino 25 acid residues as compared to any one of the amino acid sequences set forth herein. In some embodiments, proteins comprising fragments of Cas9 are provided. For example, in some embodiments, a protein comprises one of two Cas9 domains: (1) the gRNA binding domain of Cas9; or (2) the DNA cleavage domain of Cas9. In some embodiments, proteins comprising Cas9 or fragments thereof are referred to as “Cas9 variants.” A Cas9 30 variant shares homology to Cas9, or a fragment thereof. For example, a Cas9 variant is at least about 70% identical, at least about 80% identical, at least about 90% identical, at least about 95% identical, at least about 96% identical, at least about 97% identical, at least about 98% identical, at least about 99% identical, at least about 99.5% identical, or at least about 2020216484   17 Mar 2026 99.9% identical to wild-type Cas9. In some embodiments, the Cas9 variant may have 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 21, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 or more amino acid changes compared to wild-type Cas9. In some embodiments, the Cas9 variant comprises a 5 fragment of Cas9 (e.g., a gRNA binding domain or a DNA-cleavage domain), such that the fragment is at least about 70% identical, at least about 80% identical, at least about 90% identical, at least about 95% identical, at least about 96% identical, at least about 97% identical, at least about 98% identical, at least about 99% identical, at least about 99.5% identical, or at least about 99.9% identical to the corresponding fragment of wild-type Cas9. 10 In some embodiments, the fragment is at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95% identical, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% of the amino acid length of a corresponding wild-type Cas9. In some embodiments, the fragment is at least 100 amino acids in length. In some 15 embodiments, the fragment is at least 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 650, 700, 750, 800, 850, 900, 950, 1000, 1050, 1100, 1150, 1200, 1250, or at least 1300 amino acids in length. In some embodiments, Cas9 fusion proteins as provided herein comprise the full-length amino acid sequence of a Cas9 protein, e.g., one of the Cas9 sequences provided herein. In 20 other embodiments, however, fusion proteins as provided herein do not comprise a full-length Cas9 sequence, but only one or more fragments thereof. Exemplary amino acid sequences of suitable Cas9 domains and Cas9 fragments are provided herein, and additional suitable sequences of Cas9 domains and fragments will be apparent to those of skill in the art. A Cas9 protein can associate with a guide RNA that guides the Cas9 protein to a 25 specific DNA sequence that has complementary to the guide RNA. In some embodiments, the polynucleotide programmable nucleotide binding domain is a Cas9 domain, for example a nuclease active Cas9, a Cas9 nickase (nCas9), or a nuclease inactive Cas9 (dCas9). Examples of nucleic acid programmable DNA binding proteins include, without limitation, Cas9 (e.g., dCas9 and nCas9), CasX, CasY, Cpf1, Cas12b / C2C1, and Cas12c / C2C3. 30 In some embodiments, wild-type Cas9 corresponds to Cas9 from Streptococcus pyogenes (NCBI Reference Sequence: NC_017053.1, nucleotide and amino acid sequences as follows). ATGGATAAGAAATACTCAATAGGCTTAGATATCGGCACAAATAGCGTCGGATGGGCGGTGAT CACTGATGATTATAAGGTTCCGTCTAAAAAGTTCAAGGTTCTGGGAAATACAGACCGCCACA 2020216484   17 Mar 2026 GTATCAAAAAAAATCTTATAGGGGCTCTTTTATTTGGCAGTGGAGAGACAGCGGAAGCGACT CGTCTCAAACGGACAGCTCGTAGAAGGTATACACGTCGGAAGAATCGTATTTGTTATCTACA GGAGATTTTTTCAAATGAGATGGCGAAAGTAGATGATAGTTTCTTTCATCGACTTGAAGAGT CTTTTTTGGTGGAAGAAGACAAGAAGCATGAACGTCATCCTATTTTTGGAAATATAGTAGAT 5 GAAGTTGCTTATCATGAGAAATATCCAACTATCTATCATCTGCGAAAAAAATTGGCAGATTC TACTGATAAAGCGGATTTGCGCTTAATCTATTTGGCCTTAGCGCATATGATTAAGTTTCGTG GTCATTTTTTGATTGAGGGAGATTTAAATCCTGATAATAGTGATGTGGACAAACTATTTATC CAGTTGGTACAAATCTACAATCAATTATTTGAAGAAAACCCTATTAACGCAAGTAGAGTAGA TGCTAAAGCGATTCTTTCTGCACGATTGAGTAAATCAAGACGATTAGAAAATCTCATTGCTC 10 AGCTCCCCGGTGAGAAGAGAAATGGCTTGTTTGGGAATCTCATTGCTTTGTCATTGGGATTG ACCCCTAATTTTAAATCAAATTTTGATTTGGCAGAAGATGCTAAATTACAGCTTTCAAAAGA TACTTACGATGATGATTTAGATAATTTATTGGCGCAAATTGGAGATCAATATGCTGATTTGT TTTTGGCAGCTAAGAATTTATCAGATGCTATTTTACTTTCAGATATCCTAAGAGTAAATAGT GAAATAACTAAGGCTCCCCTATCAGCTTCAATGATTAAGCGCTACGATGAACATCATCAAGA 15 CTTGACTCTTTTAAAAGCTTTAGTTCGACAACAACTTCCAGAAAAGTATAAAGAAATCTTTT TTGATCAATCAAAAAACGGATATGCAGGTTATATTGATGGGGGAGCTAGCCAAGAAGAATTT TATAAATTTATCAAACCAATTTTAGAAAAAATGGATGGTACTGAGGAATTATTGGTGAAACT AAATCGTGAAGATTTGCTGCGCAAGCAACGGACCTTTGACAACGGCTCTATTCCCCATCAAA TTCACTTGGGTGAGCTGCATGCTATTTTGAGAAGACAAGAAGACTTTTATCCATTTTTAAAA 20 GACAATCGTGAGAAGATTGAAAAAATCTTGACTTTTCGAATTCCTTATTATGTTGGTCCATT GGCGCGTGGCAATAGTCGTTTTGCATGGATGACTCGGAAGTCTGAAGAAACAATTACCCCAT GGAATTTTGAAGAAGTTGTCGATAAAGGTGCTTCAGCTCAATCATTTATTGAACGCATGACA AACTTTGATAAAAATCTTCCAAATGAAAAAGTACTACCAAAACATAGTTTGCTTTATGAGTA TTTTACGGTTTATAACGAATTGACAAAGGTCAAATATGTTACTGAGGGAATGCGAAAACCAG 25 CATTTCTTTCAGGTGAACAGAAGAAAGCCATTGTTGATTTACTCTTCAAAACAAATCGAAAA GTAACCGTTAAGCAATTAAAAGAAGATTATTTCAAAAAAATAGAATGTTTTGATAGTGTTGA AATTTCAGGAGTTGAAGATAGATTTAATGCTTCATTAGGCGCCTACCATGATTTGCTAAAAA TTATTAAAGATAAAGATTTTTTGGATAATGAAGAAAATGAAGATATCTTAGAGGATATTGTT TTAACATTGACCTTATTTGAAGATAGGGGGATGATTGAGGAAAGACTTAAAACATATGCTCA 30 CCTCTTTGATGATAAGGTGATGAAACAGCTTAAACGTCGCCGTTATACTGGTTGGGGACGTT TGTCTCGAAAATTGATTAATGGTATTAGGGATAAGCAATCTGGCAAAACAATATTAGATTTT TTGAAATCAGATGGTTTTGCCAATCGCAATTTTATGCAGCTGATCCATGATGATAGTTTGAC ATTTAAAGAAGATATTCAAAAAGCACAGGTGTCTGGACAAGGCCATAGTTTACATGAACAGA TTGCTAACTTAGCTGGCAGTCCTGCTATTAAAAAAGGTATTTTACAGACTGTAAAAATTGTT 2020216484   17 Mar 2026 GATGAACTGGTCAAAGTAATGGGGCATAAGCCAGAAAATATCGTTATTGAAATGGCACGTGA AAATCAGACAACTCAAAAGGGCCAGAAAAATTCGCGAGAGCGTATGAAACGAATCGAAGAAG GTATCAAAGAATTAGGAAGTCAGATTCTTAAAGAGCATCCTGTTGAAAATACTCAATTGCAA AATGAAAAGCTCTATCTCTATTATCTACAAAATGGAAGAGACATGTATGTGGACCAAGAATT 5 AGATATTAATCGTTTAAGTGATTATGATGTCGATCACATTGTTCCACAAAGTTTCATTAAAG ACGATTCAATAGACAATAAGGTACTAACGCGTTCTGATAAAAATCGTGGTAAATCGGATAAC GTTCCAAGTGAAGAAGTAGTCAAAAAGATGAAAAACTATTGGAGACAACTTCTAAACGCCAA GTTAATCACTCAACGTAAGTTTGATAATTTAACGAAAGCTGAACGTGGAGGTTTGAGTGAAC TTGATAAAGCTGGTTTTATCAAACGCCAATTGGTTGAAACTCGCCAAATCACTAAGCATGTG 10 GCACAAATTTTGGATAGTCGCATGAATACTAAATACGATGAAAATGATAAACTTATTCGAGA GGTTAAAGTGATTACCTTAAAATCTAAATTAGTTTCTGACTTCCGAAAAGATTTCCAATTCT ATAAAGTACGTGAGATTAACAATTACCATCATGCCCATGATGCGTATCTAAATGCCGTCGTT GGAACTGCTTTGATTAAGAAATATCCAAAACTTGAATCGGAGTTTGTCTATGGTGATTATAA AGTTTATGATGTTCGTAAAATGATTGCTAAGTCTGAGCAAGAAATAGGCAAAGCAACCGCAA 15 AATATTTCTTTTACTCTAATATCATGAACTTCTTCAAAACAGAAATTACACTTGCAAATGGA GAGATTCGCAAACGCCCTCTAATCGAAACTAATGGGGAAACTGGAGAAATTGTCTGGGATAA AGGGCGAGATTTTGCCACAGTGCGCAAAGTATTGTCCATGCCCCAAGTCAATATTGTCAAGA AAACAGAAGTACAGACAGGCGGATTCTCCAAGGAGTCAATTTTACCAAAAAGAAATTCGGAC AAGCTTATTGCTCGTAAAAAAGACTGGGATCCAAAAAAATATGGTGGTTTTGATAGTCCAAC 20 GGTAGCTTATTCAGTCCTAGTGGTTGCTAAGGTGGAAAAAGGGAAATCGAAGAAGTTAAAAT CCGTTAAAGAGTTACTAGGGATCACAATTATGGAAAGAAGTTCCTTTGAAAAAAATCCGATT GACTTTTTAGAAGCTAAAGGATATAAGGAAGTTAAAAAAGACTTAATCATTAAACTACCTAA ATATAGTCTTTTTGAGTTAGAAAACGGTCGTAAACGGATGCTGGCTAGTGCCGGAGAATTAC AAAAAGGAAATGAGCTGGCTCTGCCAAGCAAATATGTGAATTTTTTATATTTAGCTAGTCAT 25 TATGAAAAGTTGAAGGGTAGTCCAGAAGATAACGAACAAAAACAATTGTTTGTGGAGCAGCA TAAGCATTATTTAGATGAGATTATTGAGCAAATCAGTGAATTTTCTAAGCGTGTTATTTTAG CAGATGCCAATTTAGATAAAGTTCTTAGTGCATATAACAAACATAGAGACAAACCAATACGT GAACAAGCAGAAAATATTATTCATTTATTTACGTTGACGAATCTTGGAGCTCCCGCTGCTTT TAAATATTTTGATACAACAATTGATCGTAAACGATATACGTCTACAAAAGAAGTTTTAGATG 30 CCACTCTTATCCATCAATCCATCACTGGTCTTTATGAAACACGCATTGATTTGAGTCAGCTA GGAGGTGACTGA MDKKYSIGLDIGTNSVGWAVITDDYKVPSKKFKVLGNTDRHSIKKNLIGALLFGSGETAEAT RLKRTARRRYTRRKNRICYLQEIFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFGNIVD 2020216484   17 Mar 2026 EVAYHEKYPTIYHLRKKLADSTDKADLRLIYLALAHMIKFRGHFLIEGDLNPDNSDVDKLFI QLVQIYNQLFEENPINASRVDAKAILSARLSKSRRLENLIAQLPGEKRNGLFGNLIALSLGL TPNFKSNFDLAEDAKLQLSKDTYDDDLDNLLAQIGDQYADLFLAAKNLSDAILLSDILRVNS EITKAPLSASMIKRYDEHHQDLTLLKALVRQQLPEKYKEIFFDQSKNGYAGYIDGGASQEEF 5 YKFIKPILEKMDGTEELLVKLNREDLLRKQRTFDNGSIPHQIHLGELHAILRRQEDFYPFLK DNREKIEKILTFRIPYYVGPLARGNSRFAWMTRKSEETITPWNFEEVVDKGASAQSFIERMT NFDKNLPNEKVLPKHSLLYEYFTVYNELTKVKYVTEGMRKPAFLSGEQKKAIVDLLFKTNRK VTVKQLKEDYFKKIECFDSVEISGVEDRFNASLGAYHDLLKIIKDKDFLDNEENEDILEDIV LTLTLFEDRGMIEERLKTYAHLFDDKVMKQLKRRRYTGWGRLSRKLINGIRDKQSGKTILDF 10 LKSDGFANRNFMQLIHDDSLTFKEDIQKAQVSGQGHSLHEQIANLAGSPAIKKGILQTVKIV DELVKVMGHKPENIVIEMARENQTTQKGQKNSRERMKRIEEGIKELGSQILKEHPVENTQLQ NEKLYLYYLQNGRDMYVDQELDINRLSDYDVDHIVPQSFIKDDSIDNKVLTRSDKNRGKSDN VPSEEVVKKMKNYWRQLLNAKLITQRKFDNLTKAERGGLSELDKAGFIKRQLVETRQITKHV AQILDSRMNTKYDENDKLIREVKVITLKSKLVSDFRKDFQFYKVREINNYHHAHDAYLNAVV 15 GTALIKKYPKLESEFVYGDYKVYDVRKMIAKSEQEIGKATAKYFFYSNIMNFFKTEITLANG EIRKRPLXETNGETGEIVWDKGRDFATVRKVLSMPQVNIVKKTEVQTGGFS KESIL PKRN S D KLIARKKDWDPKKYGGFDSPTVAYSVLVVAKVEKGKSKKLKSVKELLGITIMERSSFEKNPI DFLEAKGYKEVKKDLIIKLPKYSLFELENGRKRMLASAGELQKGNELALPSKYVNFLYLASH YEKLKGSPEDNEQKQLFVEQHKHYLDEIIEQISEFSKRVILADANLDKVLSAYNKHRDKPIR 20 EQAENIIHLFTLTNLGAPAAFKYFDTTIDRKRYTSTKEVLDATLIHQSITGLYETRIDLSQL GGD (single underline: HNH domain; double underline: RuvC domain) In some embodiments, wild-type Cas9 corresponds to, or comprises the following nucleotide and / or amino acid sequences: 25 ATGGATAAAAAGTATTCTATTGGTTTAGACATCGGCACTAATTCCGTTGGATGGGCTGTCAT AACCGATGAATACAAAGTACCTTCAAAGAAATTTAAGGTGTTGGGGAACACAGACCGTCATT CGATTAAAAAGAATCTTATCGGTGCCCTCCTATTCGATAGTGGCGAAACGGCAGAGGCGACT CGCCTGAAACGAACCGCTCGGAGAAGGTATACACGTCGCAAGAACCGAATATGTTACTTACA AGAAATTTTTAGCAATGAGATGGCCAAAGTTGACGATTCTTTCTTTCACCGTTTGGAAGAGT 30 CCTTCCTTGTCGAAGAGGACAAGAAACATGAACGGCACCCCATCTTTGGAAACATAGTAGAT GAGGTGGCATATCATGAAAAGTACCCAACGATTTATCACCTCAGAAAAAAGCTAGTTGACTC AACTGATAAAGCGGACCTGAGGTTAATCTACTTGGCTCTTGCCCATATGATAAAGTTCCGTG GGCACTTTCTCATTGAGGGTGATCTAAATCCGGACAACTCGGATGTCGACAAACTGTTCATC CAGTTAGTACAAACCTATAATCAGTTGTTTGAAGAGAACCCTATAAATGCAAGTGGCGTGGA 2020216484   17 Mar 2026 TGCGAAGGCTATTCTTAGCGCCCGCCTCTCTAAATCCCGACGGCTAGAAAACCTGATCGCAC AATTACCCGGAGAGAAGAAAAATGGGTTGTTCGGTAACCTTATAGCGCTCTCACTAGGCCTG ACACCAAATTTTAAGTCGAACTTCGACTTAGCTGAAGATGCCAAATTGCAGCTTAGTAAGGA CACGTACGATGACGATCTCGACAATCTACTGGCACAAATTGGAGATCAGTATGCGGACTTAT 5 TTTTGGCTGCCAAAAACCTTAGCGATGCAATCCTCCTATCTGACATACTGAGAGTTAATACT GAGATTACCAAGGCGCCGTTATCCGCTTCAATGATCAAAAGGTACGATGAACATCACCAAGA CTTGACACTTCTCAAGGCCCTAGTCCGTCAGCAACTGCCTGAGAAATATAAGGAAATATTCT TTGATCAGTCGAAAAACGGGTACGCAGGTTATATTGACGGCGGAGCGAGTCAAGAGGAATTC TACAAGTTTATCAAACCCATATTAGAGAAGATGGATGGGACGGAAGAGTTGCTTGTAAAACT 10 CAATCGCGAAGATCTACTGCGAAAGCAGCGGACTTTCGACAACGGTAGCATTCCACATCAAA TCCACTTAGGCGAATTGCATGCTATACTTAGAAGGCAGGAGGATTTTTATCCGTTCCTCAAA GACAATCGTGAAAAGATTGAGAAAATCCTAACCTTTCGCATACCTTACTATGTGGGACCCCT GGCCCGAGGGAACTCTCGGTTCGCATGGATGACAAGAAAGTCCGAAGAAACGATTACTCCAT GGAATTTTGAGGAAGTTGTCGATAAAGGTGCGTCAGCTCAATCGTTCATCGAGAGGATGACC 15 AACTTTGACAAGAATTTACCGAACGAAAAAGTATTGCCTAAGCACAGTTTACTTTACGAGTA TTTCACAGTGTACAATGAACTCACGAAAGTTAAGTATGTCACTGAGGGCATGCGTAAACCCG CCTTTCTAAGCGGAGAACAGAAGAAAGCAATAGTAGATCTGTTATTCAAGACCAACCGCAAA GTGACAGTTAAGCAATTGAAAGAGGACTACTTTAAGAAAATTGAATGCTTCGATTCTGTCGA GATCTCCGGGGTAGAAGATCGATTTAATGCGTCACTTGGTACGTATCATGACCTCCTAAAGA 20 TAATTAAAGATAAGGACTTCCTGGATAACGAAGAGAATGAAGATATCTTAGAAGATATAGTG TTGACTCTTACCCTCTTTGAAGATCGGGAAATGATTGAGGAAAGACTAAAAACATACGCTCA CCTGTTCGACGATAAGGTTATGAAACAGTTAAAGAGGCGTCGCTATACGGGCTGGGGACGAT TGTCGCGGAAACTTATCAACGGGATAAGAGACAAGCAAAGTGGTAAAACTATTCTCGATTTT CTAAAGAGCGACGGCTTCGCCAATAGGAACTTTATGCAGCTGATCCATGATGACTCTTTAAC 25 CTTCAAAGAGGATATACAAAAGGCACAGGTTTCCGGACAAGGGGACTCATTGCACGAACATA TTGCGAATCTTGCTGGTTCGCCAGCCATCAAAAAGGGCATACTCCAGACAGTCAAAGTAGTG GATGAGCTAGTTAAGGTCATGGGACGTCACAAACCGGAAAACATTGTAATCGAGATGGCACG CGAAAATCAAACGACTCAGAAGGGGCAAAAAAACAGTCGAGAGCGGATGAAGAGAATAGAAG AGGGTATTAAAGAACTGGGCAGCCAGATCTTAAAGGAGCATCCTGTGGAAAATACCCAATTG 30 CAGAACGAGAAACTTTACCTCTATTACCTACAAAATGGAAGGGACATGTATGTTGATCAGGA ACTGGACATAAACCGTTTATCTGATTACGACGTCGATCACATTGTACCCCAATCCTTTTTGA AGGACGATTCAATCGACAATAAAGTGCTTACACGCTCGGATAAGAACCGAGGGAAAAGTGAC AATGTTCCAAGCGAGGAAGTCGTAAAGAAAATGAAGAACTATTGGCGGCAGCTCCTAAATGC GAAACTGATAACGCAAAGAAAGTTCGATAACTTAACTAAAGCTGAGAGGGGTGGCTTGTCTG 2020216484   17 Mar 2026 AACTTGACAAGGCCGGATTTATTAAACGTCAGCTCGTGGAAACCCGCCAAATCACAAAGCAT GTTGCACAGATACTAGATTCCCGAATGAATACGAAATACGACGAGAACGATAAGCTGATTCG GGAAGTCAAAGTAATCACTTTAAAGTCAAAATTGGTGTCGGACTTCAGAAAGGATTTTCAAT TCTATAAAGTTAGGGAGATAAATAACTACCACCATGCGCACGACGCTTATCTTAATGCCGTC 5 GTAGGGACCGCACTCATTAAGAAATACCCGAAGCTAGAAAGTGAGTTTGTGTATGGTGATTA CAAAGTTTATGACGTCCGTAAGATGATCGCGAAAAGCGAACAGGAGATAGGCAAGGCTACAG CCAAATACTTCTTTTATTCTAACATTATGAATTTCTTTAAGACGGAAATCACTCTGGCAAAC GGAGAGATACGCAAACGACCTTTAATTGAAACCAATGGGGAGACAGGTGAAATCGTATGGGA TAAGGGCCGGGACTTCGCGACGGTGAGAAAAGTTTTGTCCATGCCCCAAGTCAACATAGTAA 10 AGAAAACTGAGGTGCAGACCGGAGGGTTTTCAAAGGAATCGATTCTTCCAAAAAGGAATAGT GATAAGCTCATCGCTCGTAAAAAGGACTGGGACCCGAAAAAGTACGGTGGCTTCGATAGCCC TACAGTTGCCTATTCTGTCCTAGTAGTGGCAAAAGTTGAGAAGGGAAAATCCAAGAAACTGA AGTCAGTCAAAGAATTATTGGGGATAACGATTATGGAGCGCTCGTCTTTTGAAAAGAACCCC ATCGACTTCCTTGAGGCGAAAGGTTACAAGGAAGTAAAAAAGGATCTCATAATTAAACTACC 15 AAAGTATAGTCTGTTTGAGTTAGAAAATGGCCGAAAACGGATGTTGGCTAGCGCCGGAGAGC TTCAAAAGGGGAACGAACTCGCACTACCGTCTAAATACGTGAATTTCCTGTATTTAGCGTCC CATTACGAGAAGTTGAAAGGTTCACCTGAAGATAACGAACAGAAGCAACTTTTTGTTGAGCA GCACAAACATTATCTCGACGAAATCATAGAGCAAATTTCGGAATTCAGTAAGAGAGTCATCC TAGCTGATGCCAATCTGGACAAAGTATTAAGCGCATACAACAAGCACAGGGATAAACCCATA 20 CGTGAGCAGGCGGAAAATATTATCCATTTGTTTACTCTTACCAACCTCGGCGCTCCAGCCGC ATTCAAGTATTTTGACACAACGATAGATCGCAAACGATACACTTCTACCAAGGAGGTGCTAG ACGCGACACTGATTCACCAATCCATCACGGGATTATATGAAACTCGGATAGATTTGTCACAG CTTGGGGGTGACGGATCCCCCAAGAAGAAGAGGAAAGTCTCGAGCGACTACAAAGACCATGA CGGTGATTATAAAGATCATGACATCGATTACAAGGATGACGATGACAAGGCTGCAGGA 25 MDKKYSIGLAIGTNSVGWAVITDEYKVPSKKFKVLGNTDRHSIKKNLIGALLFDSGETAEAT RLKRTARRRYTRRKNRICYLQEIFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFGNIVD EVAYHEKYPTIYHLRKKLVDSTDKADLRLIYLALAHMIKFRGHFLIEGDLNPDNSDVDKLFI QLVQTYNQLFEENPINASGVDAKAILSARLSKSRRLENLIAQLPGEKKNGLFGNLIALSLGL 30 TPNFKSNFDLAEDAKLQLSKDTYDDDLDNLLAQIGDQYADLFLAAKNLSDAILLSDILRVNT EITKAPLSASMIKRYDEHHQDLTLLKALVRQQLPEKYKEIFFDQSKNGYAGYIDGGASQEEF YKFIKPILEKMDGTEELLVKLNREDLLRKQRTFDNGSIPHQIHLGELHAILRRQEDFYPFLK DNREKIEKILTFRIPYYVGPLARGNSRFAWMTRKSEETITPWNFEEVVDKGASAQSFIERMT NFDKNLPNEKVLPKHSLLYEYFTVYNELTKVKYVTEGMRKPAFLSGEQKKAIVDLLFKTNRK 2020216484   17 Mar 2026 VTVKQLKEDYFKKIECFDSVEISGVEDRFNASLGTYHDLLKIIKDKDFLDNEENEDILEDIV LTLTLFEDREMIEERLKTYAHLFDDKVMKQLKRRRYTGWGRLSRKLINGIRDKQSGKTILDF LKSDGFANRNFMQLIHDDSLTFKE DIQKAQVSGQGDSLHEHIANLAGSPAIKKGILQTVKVV DELVKVMGRHKPENIVIEMARENQTTQKGQKNSRERMKRIEEGIKELGSQILKEHPVENTQL 5 QNEKLYLYYLQNGRDMYVDQELDINRLSDYDVDHIVPQSFLKDDSIDNKVLTRSDKNRGKSD NVPSEEVVKKMKNYWRQLLNAKLITQRKFDNLTKAERGGLSELDKAGFIKRQLVETRQITKH VAQILDSRMNTKYDENDKLIREVKVITLKSKLVSDFRKDFQFYKVREINNYHHAHDAYLNAV VGTALIKKYPKLESEFVYGDYKVYDVRKMIAKSEQEIGKATAKYFFYSNIMNFFKTEITLAN GEIRKRPLIETNGETGEIVWDKGRDFATVRKVLSMPQVNIVKKTEVQTGGFSKESILPKRNS 10 DKLIARKKDWDPKKYGGFDSPTVAYSVLVVAKVEKGKSKKLKSVKELLGITIMERSSFEKNP IDFLEAKGYKEVKKDLIIKLPKYSLFELENGRKRMLASAGELQKGNELALPSKYVNFLYLAS HYEKLKGSPEDNEQKQLFVEQHKHYLDEIIEQISEFSKRVILADANLDKVLSAYNKHRDKPI REQAENIIHLFTLTNLGAPAAFKYFDTTIDRKRYTSTKEVLDATLIHQSITGLYETRIDLSQ LGGD 15 (single underline: HNH domain; double underline: RuvC domain). In some embodiments, wild-type Cas9 corresponds to Cas9 from Streptococcus pyogenes (NCBI Reference Sequence: NC_002737.2 (nucleotide sequence as follows); and Uniprot Reference Sequence: Q99ZW2 (amino acid sequence as follows): ATGGATAAGAAATACTCAATAGGCTTAGATATCGGCACAAATAGCGTCGGATGGGCGGTGAT 20 CACTGATGAATATAAGGTTCCGTCTAAAAAGTTCAAGGTTCTGGGAAATACAGACCGCCACA GTATCAAAAAAAATCTTATAGGGGCTCTTTTATTTGACAGTGGAGAGACAGCGGAAGCGACT CGTCTCAAACGGACAGCTCGTAGAAGGTATACACGTCGGAAGAATCGTATTTGTTATCTACA GGAGATTTTTTCAAATGAGATGGCGAAAGTAGATGATAGTTTCTTTCATCGACTTGAAGAGT CTTTTTTGGTGGAAGAAGACAAGAAGCATGAACGTCATCCTATTTTTGGAAATATAGTAGAT 25 GAAGTTGCTTATCATGAGAAATATCCAACTATCTATCATCTGCGAAAAAAATTGGTAGATTC TACTGATAAAGCGGATTTGCGCTTAATCTATTTGGCCTTAGCGCATATGATTAAGTTTCGTG GTCATTTTTTGATTGAGGGAGATTTAAATCCTGATAATAGTGATGTGGACAAACTATTTATC CAGTTGGTACAAACCTACAATCAATTATTTGAAGAAAACCCTATTAACGCAAGTGGAGTAGA TGCTAAAGCGATTCTTTCTGCACGATTGAGTAAATCAAGACGATTAGAAAATCTCATTGCTC 30 AGCTCCCCGGTGAGAAGAAAAATGGCTTATTTGGGAATCTCATTGCTTTGTCATTGGGTTTG ACCCCTAATTTTAAATCAAATTTTGATTTGGCAGAAGATGCTAAATTACAGCTTTCAAAAGA TACTTACGATGATGATTTAGATAATTTATTGGCGCAAATTGGAGATCAATATGCTGATTTGT TTTTGGCAGCTAAGAATTTATCAGATGCTATTTTACTTTCAGATATCCTAAGAGTAAATACT GAAATAACTAAGGCTCCCCTATCAGCTTCAATGATTAAACGCTACGATGAACATCATCAAGA 2020216484   17 Mar 2026 CTTGACTCTTTTAAAAGCTTTAGTTCGACAACAACTTCCAGAAAAGTATAAAGAAATCTTTT TTGATCAATCAAAAAACGGATATGCAGGTTATATTGATGGGGGAGCTAGCCAAGAAGAATTT TATAAATTTATCAAACCAATTTTAGAAAAAATGGATGGTACTGAGGAATTATTGGTGAAACT AAATCGTGAAGATTTGCTGCGCAAGCAACGGACCTTTGACAACGGCTCTATTCCCCATCAAA 5 TTCACTTGGGTGAGCTGCATGCTATTTTGAGAAGACAAGAAGACTTTTATCCATTTTTAAAA GACAATCGTGAGAAGATTGAAAAAATCTTGACTTTTCGAATTCCTTATTATGTTGGTCCATT GGCGCGTGGCAATAGTCGTTTTGCATGGATGACTCGGAAGTCTGAAGAAACAATTACCCCAT GGAATTTTGAAGAAGTTGTCGATAAAGGTGCTTCAGCTCAATCATTTATTGAACGCATGACA AACTTTGATAAAAATCTTCCAAATGAAAAAGTACTACCAAAACATAGTTTGCTTTATGAGTA 10 TTTTACGGTTTATAACGAATTGACAAAGGTCAAATATGTTACTGAAGGAATGCGAAAACCAG CATTTCTTTCAGGTGAACAGAAGAAAGCCATTGTTGATTTACTCTTCAAAACAAATCGAAAA GTAACCGTTAAGCAATTAAAAGAAGATTATTTCAAAAAAATAGAATGTTTTGATAGTGTTGA AATTTCAGGAGTTGAAGATAGATTTAATGCTTCATTAGGTACCTACCATGATTTGCTAAAAA TTATTAAAGATAAAGATTTTTTGGATAATGAAGAAAATGAAGATATCTTAGAGGATATTGTT 15 TTAACATTGACCTTATTTGAAGATAGGGAGATGATTGAGGAAAGACTTAAAACATATGCTCA CCTCTTTGATGATAAGGTGATGAAACAGCTTAAACGTCGCCGTTATACTGGTTGGGGACGTT TGTCTCGAAAATTGATTAATGGTATTAGGGATAAGCAATCTGGCAAAACAATATTAGATTTT TTGAAATCAGATGGTTTTGCCAATCGCAATTTTATGCAGCTGATCCATGATGATAGTTTGAC ATTTAAAGAAGACATTCAAAAAGCACAAGTGTCTGGACAAGGCGATAGTTTACATGAACATA 20 TTGCAAATTTAGCTGGTAGCCCTGCTATTAAAAAAGGTATTTTACAGACTGTAAAAGTTGTT GATGAATTGGTCAAAGTAATGGGGCGGCATAAGCCAGAAAATATCGTTATTGAAATGGCACG TGAAAATCAGACAACTCAAAAGGGCCAGAAAAATTCGCGAGAGCGTATGAAACGAATCGAAG AAGGTATCAAAGAATTAGGAAGTCAGATTCTTAAAGAGCATCCTGTTGAAAATACTCAATTG CAAAATGAAAAGCTCTATCTCTATTATCTCCAAAATGGAAGAGACATGTATGTGGACCAAGA 25 ATTAGATATTAATCGTTTAAGTGATTATGATGTCGATCACATTGTTCCACAAAGTTTCCTTA AAGACGATTCAATAGACAATAAGGTCTTAACGCGTTCTGATAAAAATCGTGGTAAATCGGAT AACGTTCCAAGTGAAGAAGTAGTCAAAAAGATGAAAAACTATTGGAGACAACTTCTAAACGC CAAGTTAATCACTCAACGTAAGTTTGATAATTTAACGAAAGCTGAACGTGGAGGTTTGAGTG AACTTGATAAAGCTGGTTTTATCAAACGCCAATTGGTTGAAACTCGCCAAATCACTAAGCAT 30 GTGGCACAAATTTTGGATAGTCGCATGAATACTAAATACGATGAAAATGATAAACTTATTCG AGAGGTTAAAGTGATTACCTTAAAATCTAAATTAGTTTCTGACTTCCGAAAAGATTTCCAAT TCTATAAAGTACGTGAGATTAACAATTACCATCATGCCCATGATGCGTATCTAAATGCCGTC GTTGGAACTGCTTTGATTAAGAAATATCCAAAACTTGAATCGGAGTTTGTCTATGGTGATTA TAAAGTTTATGATGTTCGTAAAATGATTGCTAAGTCTGAGCAAGAAATAGGCAAAGCAACCG 2020216484   17 Mar 2026 CAAAATATTTCTTTTACTCTAATATCATGAACTTCTTCAAAACAGAAATTACACTTGCAAAT GGAGAGATTCGCAAACGCCCTCTAATCGAAACTAATGGGGAAACTGGAGAAATTGTCTGGGA TAAAGGGCGAGATTTTGCCACAGTGCGCAAAGTATTGTCCATGCCCCAAGTCAATATTGTCA AGAAAACAGAAGTACAGACAGGCGGATTCTCCAAGGAGTCAATTTTACCAAAAAGAAATTCG 5 GACAAGCTTATTGCTCGTAAAAAAGACTGGGATCCAAAAAAATATGGTGGTTTTGATAGTCC AACGGTAGCTTATTCAGTCCTAGTGGTTGCTAAGGTGGAAAAAGGGAAATCGAAGAAGTTAA AATCCGTTAAAGAGTTACTAGGGATCACAATTATGGAAAGAAGTTCCTTTGAAAAAAATCCG ATTGACTTTTTAGAAGCTAAAGGATATAAGGAAGTTAAAAAAGACTTAATCATTAAACTACC TAAATATAGTCTTTTTGAGTTAGAAAACGGTCGTAAACGGATGCTGGCTAGTGCCGGAGAAT 10 TACAAAAAGGAAATGAGCTGGCTCTGCCAAGCAAATATGTGAATTTTTTATATTTAGCTAGT CATTATGAAAAGTTGAAGGGTAGTCCAGAAGATAACGAACAAAAACAATTGTTTGTGGAGCA GCATAAGCATTATTTAGATGAGATTATTGAGCAAATCAGTGAATTTTCTAAGCGTGTTATTT TAGCAGATGCCAATTTAGATAAAGTTCTTAGTGCATATAACAAACATAGAGACAAACCAATA CGTGAACAAGCAGAAAATATTATTCATTTATTTACGTTGACGAATCTTGGAGCTCCCGCTGC 15 TTTTAAATATTTTGATACAACAATTGATCGTAAACGATATACGTCTACAAAAGAAGTTTTAG ATGCCACTCTTATCCATCAATCCATCACTGGTCTTTATGAAACACGCATTGATTTGAGTCAG CTAGGAGGTGACTGA MDKKYSIGLDIGTNSVGWAVITDEYKVPSKKFKVLGNTDRHSIKKNLIGALLFDSGETAEAT 20 RLKRTARRRYTRRKNRICYLQEIFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFGNIVD EVAYHEKYPTIYHLRKKLVDSTDKADLRLIYLALAHMIKFRGHFLIEGDLNPDNSDVDKLFI QLVQTYNQLFEENPINASGVDAKAILSARLSKSRRLENLIAQLPGEKKNGLFGNLIALSLGL TPNFKSNFDLAEDAKLQLSKDTYDDDLDNLLAQIGDQYADLFLAAKNLSDAILLSDILRVNT EITKAPLSASMIKRYDEHHQDLTLLKALVRQQLPEKYKEIFFDQSKNGYAGYIDGGASQEEF 25 YKFIKPILEKMDGTEELLVKLNREDLLRKQRTFDNGSIPHQIHLGELHAILRRQEDFYPFLK DNREKIEKILTFRIPYYVGPLARGNSRFAWMTRKSEETITPWNFEEVVDKGASAQSFIERMT NFDKNLPNEKVLPKHSLLYEYFTVYNELTKVKYVTEGMRKPAFLSGEQKKAIVDLLFKTNRK VTVKQLKEDYFKKIECFDSVEISGVEDRFNASLGTYHDLLKIIKDKDFLDNEENEDILEDIV LTLTLFEDREMIEERLKTYAHLFDDKVMKQLKRRRYTGWGRLSRKLINGIRDKQSGKTILDF 30 LKSDGFANRNFMQLIHDDSLTFKEDIQKAQVSGQGDSLHEHIANLAGSPAIKKGILQTVKVV DELVKVMGRHKPENIVIEMARENQTTQKGQKNSRERMKRIEEGIKELGSQILKEHPVENTQL QNEKLYLYYLQNGRDMYVDQELDINRLSDYDVDHIVPQSFLKDDSIDNKVLTRSDKNRGKSD NVPSEEVVKKMKNYWRQLLNAKLITQRKFDNLTKAERGGLSELDKAGFIKRQLVETRQITKH VAQXLDSRMNTKYDENDKLIREVKVITLKSKLVSDFRKDFQFYKVREINNyHHAHDAYLNAV 2020216484   17 Mar 2026 VGTALIKKYPKLESEFVYGDYKVYDVRKMIAKSEQEIGKATAKYFFYSNIMNFFKTEITLAN GEIRKRPLIETNGETGEIVWDKGRDFATVRKVLSMPQVNIVKKTEVQTGGFSKESIL PKRNS DKLIARKKDWDPKKYGGFDSPTVAYSVLVVAKVEKGKSKKLKSVKELLGITIMERSSFEKNP IDFLEAKGYKEVKKDLIIKLPKYSLFELENGRKRMLASAGELQKGNELALPSKYVNFLYLAS 5 HYEKLKGSPEDNEQKQLFVEQHKHYLDEIIEQISEFSKRVILADANLDKVLSAYNKHRDKPI REQAENIIHLFTLTNLGAPAAFKYFDTTIDRKRYTSTKEVLDATLIHQSITGLYETRIDLSQ LGGD (single underline: HNH domain; double underline: RuvC domain) In some embodiments, Cas9 refers to Cas9 from: Corynebacterium ulcerans (NCBI Refs: NC_015683.1, NC_017317.1); Corynebacterium diphtheria (NCBI Refs: 10   NC_016782.1, NC_016786.1); Spiroplasma syrphidicola (NCBI Ref: NC_021284.1); Prevotella intermedia (NCBI Ref: NC_017861.1); Spiroplasma taiwanense (NCBI Ref: NC_021846.1); Streptococcus iniae (NCBI Ref: NC_021314.1); Belliella baltica (NCBI Ref: NC_018010.1); Psychroflexus torquisI (NCBI Ref: NC_018721.1); Streptococcus thermophilus (NCBI Ref: YP_820832.1), Listeria innocua (NCBI Ref: NP_472073.1), 15   Campylobacter jejuni (NCBI Ref: YP_002344900.1) or Neisseria meningitidis (NCBI Ref: YP_002342100.1) or to a Cas9 from any other organism. It should be appreciated that additional Cas9 proteins (e.g., a nuclease dead Cas9 (dCas9), a Cas9 nickase (nCas9), or a nuclease active Cas9), including variants and homologs thereof, are within the scope of this disclosure. Exemplary Cas9 proteins include, without 20 limitation, those provided below. In some embodiments, the Cas9 protein is a nuclease dead Cas9 (dCas9). In some embodiments, the Cas9 protein is a Cas9 nickase (nCas9). In some embodiments, the Cas9 protein is a nuclease active Cas9. In some embodiments, the Cas9 domain is a nuclease-inactive Cas9 domain (dCas9). For example, the dCas9 domain may bind to a duplexed nucleic acid molecule (e.g., via a 25 gRNA molecule) without cleaving either strand of the duplexed nucleic acid molecule. In some embodiments, the nuclease-inactive dCas9 domain comprises a D10X mutation and a H840X mutation of the amino acid sequence set forth herein, or a corresponding mutation in any of the amino acid sequences provided herein, wherein X is any amino acid change. In some embodiments, the nuclease-inactive dCas9 domain comprises a D10A mutation and a 30   H840A mutation of the amino acid sequence set forth herein, or a corresponding mutation in any of the amino acid sequences provided herein. As one example, a nuclease-inactive Cas9 domain comprises the amino acid sequence set forth in Cloning vector pPlatTET-gRNA2 (Accession No. BAV54124). 2020216484   17 Mar 2026 The amino acid sequence of an exemplary catalytically inactive Cas9 (dCas9) is as follows: MDKKYSIGLAIGTNSVGWAVITDEYKVPSKKFKVLGNTDRHSIKKNLIGALLFDSGETAEAT RLKRTARRRYTRRKNRICYLQEIFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFGNIVD 5 EVAYHEKYPTIYHLRKKLVDSTDKADLRLIYLALAHMIKFRGHFLIEGDLNPDNSDVDKLFI QLVQTYNQLFEENPINASGVDAKAILSARLSKSRRLENLIAQLPGEKKNGLFGNLIALSLGL TPNFKSNFDLAEDAKLQLSKDTYDDDLDNLLAQIGDQYADLFLAAKNLSDAILLSDILRVNT EITKAPLSASMIKRYDEHHQDLTLLKALVRQQLPEKYKEIFFDQSKNGYAGYIDGGASQEEF YKFIKPILEKMDGTEELLVKLNREDLLRKQRTFDNGSIPHQIHLGELHAILRRQEDFYPFLK 10 DNREKIEKILTFRIPYYVGPLARGNSRFAWMTRKSEETITPWNFEEVVDKGASAQSFIERMT NFDKNLPNEKVLPKHSLLYEYFTVYNELTKVKYVTEGMRKPAFLSGEQKKAIVDLLFKTNRK VTVKQLKEDYFKKIECFDSVEISGVEDRFNASLGTYHDLLKIIKDKDFLDNEENEDILEDIV LTLTLFEDREMIEERLKTYAHLFDDKVMKQLKRRRYTGWGRLSRKLINGIRDKQSGKTILDF LKSDGFANRNFMQLIHDDSLTFKEDIQKAQVSGQGDSLHEHIANLAGSPAIKKGILQTVKVV 15 DELVKVMGRHKPENIVIEMARENQTTQKGQKNSRERMKRIEEGIKELGSQILKEHPVENTQL QNEKLYLYYLQNGRDMYVDQELDINRLSDYDVDAIVPQSFLKDDSIDNKVLTRSDKNRGKSD NVPSEEVVKKMKNYWRQLLNAKLITQRKFDNLTKAERGGLSELDKAGFIKRQLVETRQITKH VAQILDSRMNTKYDENDKLIREVKVITLKSKLVSDFRKDFQFYKVREINNYHHAHDAYLNAV VGTALIKKYPKLESEFVYGDYKVYDVRKMIAKSEQEIGKATAKYFFYSNIMNFFKTEITLAN 20 GEIRKRPLIETNGETGEIVWDKGRDFATVRKVLSMPQVNIVKKTEVQTGGFSKESILPKRNS DKLIARKKDWDPKKYGGFDSPTVAYSVLVVAKVEKGKSKKLKSVKELLGITIMERSSFEKNP IDFLEAKGYKEVKKDLIIKLPKYSLFELENGRKRMLASAGELQKGNELALPSKYVNFLYLAS HYEKLKGSPEDNEQKQLFVEQHKHYLDEIIEQISEFSKRVILADANLDKVLSAYNKHRDKPI REQAENIIHLFTLTNLGAPAAFKYFDTTIDRKRYTSTKEVLDATLIHQSITGLYETRIDLSQ 25 LGGD (see, e.g., Qi et al., “Repurposing CRISPR as an RNA-guided platform for sequencespecific control of gene expression.” Cell. 2013; 152(5):1173-83, the entire contents of which are incorporated herein by reference). Additional suitable nuclease-inactive dCas9 domains will be apparent to those of skill in the art based on this disclosure and knowledge in the field, and are within the scope of this 30 disclosure. Such additional exemplary suitable nuclease-inactive Cas9 domains include, but are not limited to, D10A / H840A, D10A / D839A / H840A, and D10A / D839A / H840A / N863A mutant domains (See, e.g., Prashant et al., CAS9 transcriptional activators for target specificity screening and paired nickases for cooperative genome engineering. Nature 2020216484   17 Mar 2026 Biotechnology. 2013; 31(9): 833-838, the entire contents of which are incorporated herein by reference). In some embodiments, a Cas9 nuclease has an inactive (e.g., an inactivated) DNA cleavage domain, that is, the Cas9 is a nickase, referred to as an “nCas9” protein (for 5 “nickase” Cas9). A nuclease-inactivated Cas9 protein may interchangeably be referred to as a “dCas9” protein (for nuclease-“dead” Cas9) or catalytically inactive Cas9. Methods for generating a Cas9 protein (or a fragment thereof) having an inactive DNA cleavage domain are known (See, e.g., Jinek et al., Science. 337:816-821(2012); Qi et al., “Repurposing CRISPR as an RNA-Guided Platform for Sequence-Specific Control of Gene Expression” 10   (2013) Cell. 28;152(5):1173-83, the entire contents of each of which are incorporated herein by reference). For example, the DNA cleavage domain of Cas9 is known to include two subdomains, the HNH nuclease subdomain and the RuvC1 subdomain. The HNH subdomain cleaves the strand complementary to the gRNA, whereas the RuvC1 subdomain cleaves the non-complementary strand. Mutations within these subdomains can silence the nuclease 15 activity of Cas9. For example, the mutations D10A and H840A completely inactivate the nuclease activity of S. pyogenes Cas9 (Jinek et al., Science. 337:816-821(2012); Qi et al., Cell. 28;152(5):1173-83 (2013)). In some embodiments, the dCas9 domain comprises an amino acid sequence that is at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at 20 least 95%, at least 96%, at least 97%, at least 98%, at least 99%, or at least 99.5% identical to any one of the dCas9 domains provided herein. In some embodiments, the Cas9 domain comprises an amino acid sequences that has 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 21, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50 or more or more mutations compared to any one of the 25 amino acid sequences set forth herein. In some embodiments, the Cas9 domain comprises an amino acid sequence that has at least 10, at least 15, at least 20, at least 30, at least 40, at least 50, at least 60, at least 70, at least 80, at least 90, at least 100, at least 150, at least 200, at least 250, at least 300, at least 350, at least 400, at least 500, at least 600, at least 700, at least 800, at least 900, at least 1000, at least 1100, or at least 1200 identical contiguous amino acid 30 residues as compared to any one of the amino acid sequences set forth herein. In some embodiments, dCas9 corresponds to, or comprises in part or in whole, a Cas9 amino acid sequence having one or more mutations that inactivate the Cas9 nuclease activity. 2020216484   17 Mar 2026 For example, in some embodiments, a dCas9 domain comprises D10A and an H840A mutation or corresponding mutations in another Cas9. In some embodiments, the dCas9 comprises the amino acid sequence of dCas9 (D10A and H840A): 5 MDKKYSIGLAIGTNSVGWAVITDEYKVPSKKFKVLGNTDRHSIKKNLIGALLFDSGETAEAT RLKRTARRRYTRRKNRICYLQEIFSNEMAKVDDSFFHRLEESFLVEEDKKHERHPIFGNIVD EVAYHEKYPTIYHLRKKLVDSTDKADLRLIYLALAHMIKFRGHFLIEGDLNPDNSDVDKLFI QLVQTYNQLFEENPINASGVDAKAILSARLSKSRRLENLIAQLPGEKKNGLFGNLIALSLGL TPNFKSNFDLAEDAKLQLSKDTYDDDLDNLLAQIGDQYADLFLAAKNLSDAILLSDILRVNT 10 EITKAPLSASMIKRYDEHHQDLTLLKALVRQQLPEKYKEIFFDQSKNGYAGYIDGGASQEEF YKFIKPILEKMDGTEELLVKLNREDLLRKQRTFDNGSIPHQIHLGELHAILRRQEDFYPFLK DNREKIEKILTFRIPYYVGPLARGNSRFAWMTRKSEETITPWNFEEVVDKGASAQSFIERMT NFDKNLPNEKVLPKHSLLYEYFTVYNELTKVKYVTEGMRKPAFLSGEQKKAIVDLLFKTNRK VTVKQLKEDYFKKIECFDSVEISGVEDRFNASLGTYHDLLKIIKDKDFLDNEENEDILEDIV 15 LTLTLFEDREMIEERLKTYAHLFDDKVMKQLKRRRYTGWGRLSRKLINGIRDKQSGKTILDF LKSDGFANRNFMQLIHDDSLTFKE DIQKAQVSGQGDSLHEHIANLAGSPAIKKGILQTVKVV DELVKVMGRHKPENIVIEMARENQTTQKGQKNSRERMKRIEEGIKELGSQILKEHPVENTQL QNEKLYLYYLQNGRDMYVDQELDINRLSDYDVDAIVPQSFLKDDSIDNKVLTRSDKNRGKSD NVPSEEVVKKMKNYWRQLLNAKLITQRKFDNLTKAERGGLSELDKAGF1KRQLVETRQITKH 20 VAQILDSRMNTKYDENDKLIREVKVITLKSKLVSDFRKDFQFYKVREINNYHHAHDAYLNAV VGTALIKKYPKLESEFVYGDYKVYDVRKMIAKSEQEIGKATAKYFFYSNIMNFFKTEITLAN GEIRKRPLIETNGETGEIVWDKGRDFATVRKVLSMPQVNIVKKTEVQTGGFSKESILPKRNS DKLIARKKDWDPKKYGGFDSPTVAYSVLVVAKVEKGKSKKLKSVKELLGITIMERSSFEKNP IDFLEAKGYKEVKKDLIIKLPKYSLFELENGRKRMLASAGELQKGNELALPSKYVNFLYLAS 25 HYEKLKGSPEDNEQKQLFVEQHKHYLDEIIEQISEFSKRVILADANLDKVLSAYNKHRDKPI REQAENIIHLFTLTNLGAPAAFKYFDTTIDRKRYTSTKEVLDATLIHQSITGLYETRIDLSQ LGGD (single underline: HNH domain; double underline: RuvC domain). In some embodiments, the Cas9 domain comprises a D10A mutation, while the residue at position 840 remains a histidine in the amino acid sequence provided above, or at 30 corresponding positions in any of the amino acid sequences provided herein. In other embodiments, dCas9 variants having mutations other than D10A and H840A are provided, which, e.g., result in nuclease inactivated Cas9 (dCas9). Such mutations, by way of example, include other amino acid substitutions at D10 and H840, or other substitutions within the nuclease domains of Cas9 (e.g., substitutions in the HNH nuclease 2020216484   17 Mar 2026 subdomain and / or the RuvC1 subdomain). In some embodiments, variants or homologues of dCas9 are provided which are at least about 70% identical, at least about 80% identical, at least about 90% identical, at least about 95% identical, at least about 98% identical, at least about 99% identical, at least about 99.5% identical, or at least about 99.9% identical. In 5 some embodiments, variants of dCas9 are provided having amino acid sequences which are shorter, or longer, by abou...

Claims

1. A cytidine base editor fusion protein comprising (i) a polynucleotide programmable DNA binding domain and (ii) a cytidine deaminase comprising an amino acid sequence with at least 90% sequence identity to the amino acid sequenceMTSEKGPSTGDPTLRRRIESWEFDVFYDPRELRKETCLLYEIKWGMSRKIWRSSGKNTTNHVEV NFIKKFTSERRFHSSISCSITWFLSWSPCWECSQAIREFLSQHPGVTLVIYVARLFWHMDQRNR QGLRDLVNSGVTIQIMRASEYYHCWRNFVNYPPGDEAHWPQYPPLWMMLYALELHCIILSLPPC LKISRRWQNHLAFFRLHLQNCHYQTIPPHILLATGLIHPSVTWR and further comprising an alteration selected from the group consisting of R33A, K34A, R52A, and H122A,wherein the cytidine base editor fusion protein has an increased ratio of in cis to in trans activity (in cis:in trans) as compared to a standard cytidine base editor fusion protein comprising a rat APOBEC-1 cytidine deaminase (rAPOBEC-1) and a Cas9 nickase.

2. The cytidine base editor fusion protein of claim 1, comprising one or more of:(a) the standard cytidine base editor fusion protein comprises a uracil glycosylase inhibitor (UGI) domain;(b) the standard cytidine base editor fusion protein is a BE3 or BE4;(c) the ratio of in cis to in trans activity is increased by at least 2, 2.5, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60 fold or more;(d) the cytidine base editor fusion protein has at least 50%, 60%, 70%, 80%, 90%, 95%, 100%, 105%, 110%, 115%, 120%, or more in cis activity as compared to the standard cytidine base editor fusion protein; and(e) the cytidine base editor fusion protein has at least 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 60, or more fold less in trans activity as compared to the standard cytidine base editor fusion protein.

3. The cytidine base editor fusion protein of claim 1 or claim 2, comprising one or more of: (a) the cytidine deaminase comprises one or more alterations at positions R15X, R16X, H21X, R30X, R33X, K34X, R52X, K60X, R118X, H121X, H122X, R126X, R128X, R169X, R198X,2020216484   05 Aug 2026T36X, H53X, V62X, L88X, W90X, Y120X or R132X as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof, wherein X is any amino acid;(b) the cytidine deaminase comprises one or more alterations selected from the group consisting of R15A, R16A, H21A, R30A, R33A, K34A, R52A, K60A, R118A, H121A, H122A, H122L, R126A, R128A, R169A, R198A, T36A, H53A, V62A, L88A, W90F, W90A, Y120F, Y120A, H121R, H122R, R126E, W90Y, and R132E as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof;(c) the cytidine deaminase comprises a combination of alterations selected from the group consisting of: K34A+R33A, K34A+H122A, K34A+Y120F, K34A+R52A, K34A+H122A, K34A+H121A, W90A+ R126E, W90Y+R126E, H121R+H122R, R126+R132E, W90Y+R132E, and W90Y+R126E+R132E as numbered in SEQ ID NO: 1, or corresponding alterations thereof;(d) the cytidine deaminase comprises an alteration at position Y120F and one or more alterations selected from the group consisting of R33A, W90F, K34A, R52A, H122A, and H121A as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof;(e) the cytidine deaminase comprises an alterations at position Y130X or R28X as numbered in SEQ ID NO: 1, or a corresponding alteration thereof, wherein X is any amino acid;(f) the cytidine deaminase comprises an alterations at position Y130A or R28A as numbered in SEQ ID NO: 1 or a corresponding alteration thereof;(g) the cytidine deaminase comprises alterations at positions Y130A and R28A as numbered in SEQ ID NO: 1 or corresponding alterations thereof;(h) the cytidine deaminase comprises one or more alterations at positions H122X, K34X, R33X, W90X, or R128X as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof, wherein X is any amino acid;(i) the cytidine deaminase comprises one or more alterations selected from the group consisting of H122A, K34A, R33A, W90F, W90A, and R128A as numbered in SEQ ID NO: 1, or one or more corresponding alterations thereof;(j) the cytidine deaminase comprises a combination of alterations selected from the group consisting of: R33A+K34A, W90F+K34A, R33A+K34A+W90F, and R33A+K34A+H122A+W90F as numbered in SEQ ID NO: 1 or corresponding alterations thereof;2020216484   05 Aug 2026(k) the cytidine deaminase comprises an amino acid sequence that has at least 95% identity to amino acid sequence:MTSEKGPSTGDPTLRRRIESWEFDVFYDPRELRKETCLLYEIKWGMSRKIWRSSGKNTTNHVEV NFIKKFTSERRFHSSISCSITWFLSWSPCWECSQAIREFLSQHPGVTLVIYVARLFWHMDQRNR QGLRDLVNSGVTIQIMRASEYYHCWRNFVNYPPGDEAHWPQYPPLWMMLYALELHCIILSLPPC LKISRRWQNHLAFFRLHLQNCHYQTIPPHILLATGLIHPSVTWR; and(l) the cytidine deaminase comprises the H122A alteration.

4. The cytidine base editor fusion protein of any one of claims 1-3, comprising one or more of:(a) the cytidine base editor fusion protein further comprises at least one adenosine deaminase or catalytically active fragments thereof;(b) the cytidine base editor fusion protein further comprises at least one adenosine deaminase or catalytically active fragments thereof, and the adenosine deaminase is a TadA deaminase;(c) the cytidine base editor fusion protein further comprises at least one adenosine deaminase or catalytically active fragments thereof, and the adenosine deaminase is a modified TadA deaminase that does not occur in nature;(d) the cytidine base editor fusion protein comprises two adenosine deaminases that are the same or different;(e) the cytidine base editor fusion protein comprises two adenosine deaminases that are the same or different, and the two adenosine deaminases are capable of forming heterodimers or homodimers;(f) the cytidine base editor fusion protein comprises two adenosine deaminases that are the same or different, and the adenosine deaminase domains are a wild-type TadA and TadA7.10;(g) the cytidine base editor fusion protein further comprises at least one adenosine deaminase or catalytically active fragments thereof, and the at least one adenosine deaminase comprises an adenosine deaminase comprising a deletion of the C-terminus beginning at a residue selected from the group consisting of 149, 150, 151, 152, 153, 154, 155, 156, and 157;(h) the cytidine base editor fusion protein further comprises at least one adenosine deaminase or catalytically active fragments thereof, and the at least one adenosine deaminase comprises an2020216484   05 Aug 2026adenosine deaminase missing 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 6, 17, 18, 19, or 20 N-terminal amino acid residues relative to a full-length adenosine deaminase;(i) the cytidine base editor fusion protein further comprises at least one adenosine deaminase or catalytically active fragments thereof, and the at least one adenosine deaminase comprises an adenosine deaminase missing 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 6, 17, 18, 19, or 20 C-terminal amino acid residues relative to a full-length adenosine deaminase;(j) the cytidine base editor fusion protein further comprises an abasic nucleobase editor;(k) the cytidine base editor fusion protein further comprises one or more Nuclear Localization Signals (NLS);(l) the cytidine base editor fusion protein further comprises an N-terminal NLS and / or a C-terminal NLS; and(m) the cytidine base editor fusion protein further comprises one or more bipartite NLS.

5. The cytidine base editor fusion protein of any one of claims 1-4, comprising one or more of:(a) the polynucleotide programmable DNA binding domain is a Cas9;(b) the polynucleotide programmable DNA binding domain is a Staphylococcus aureus Cas9 (SaCas9), a Streptococcus pyogenes Cas9 (SpCas9), or variants thereof;(c) the polynucleotide programmable DNA binding domain comprises a nuclease dead Cas9 (dCas9), a Cas9 nickase (nCas9), or a nuclease active Cas9;(d) the polynucleotide programmable DNA binding domain comprises a catalytic domain capable of cleaving the reverse complement strand of the nucleic acid sequence;(e) the polynucleotide programmable DNA binding domain does not comprise a catalytic domain capable of cleaving the nucleic acid sequence;(f) the polynucleotide programmable DNA binding domain is a Cas9, and the Cas9 is a dCas9;(g) the polynucleotide programmable DNA binding domain is a Cas9, and the Cas9 is a Cas9 nickase (nCas9);(h) the polynucleotide programmable DNA binding domain is a Cas9 nickase (nCas9), and the nCas9 comprises amino acid substitution D10A or a corresponding amino acid substitution thereof;2020216484   05 Aug 2026(i) the cytidine base editor fusion protein further comprises one or more Uracil DNA glycosylase inhibitors (UGI);(j) the cytidine base editor fusion protein further comprises one or more Uracil DNA glycosylase inhibitors (UGI), and the one or more UGI is derived from Bacillus subtilis bacteriophage PBS1 and inhibits human UDG activity;(k) the cytidine base editor fusion protein comprises two Uracil DNA glycosylase inhibitors (UGI); and(l) the cytidine base editor fusion protein further comprises one or more linkers.

6. A cell comprising the cytidine base editor fusion protein of any one of claims 1-5, with the proviso that the cell is not a human ovum, a human totipotent cell, a human zygote, or a human embryonic cell.

7. The cell of claim 6, wherein the cell is a bacterial cell, plant cell, insect cell, or mammalian cell.

8. A molecular complex comprising the cytidine base editor fusion protein of any one of claims 1-5 and one or more of a guide RNA, a tracrRNA, or a target DNA molecule.

9. A method of editing a nucleobase of a DNA molecule, the method comprising contacting the DNA molecule with the cytidine base editor fusion protein of any one of claims 1-5 and converting a first nucleobase of the DNA molecule to a second nucleobase, with the proviso that, if the method is performed in vivo, the contacting is not made in a human ovum, a human totipotent cell, a human zygote, or a human embryo.

10. The method of claim 9, comprising one or more of:(a) the method further comprises contacting the DNA molecule with a guide polynucleotide to effect the conversion; and(b) the first nucleobase is cytosine and the second nucleobase is thymidine.2020216484   05 Aug 202611. A polynucleotide molecule encoding the cytidine base editor fusion protein of any one of claims 1-5.

12. The polynucleotide molecule of claim 11, wherein the polynucleotide molecule is codon optimized.

13. An expression vector comprising a polynucleotide molecule of claim 11 or claim 12.

14. A kit comprising the cytidine base editor fusion protein of any one of claims 1-5, the cell of claim 6 or claim 7, the molecular complex of claim 8, the polynucleotide of claim 11 or claim 12, or the expression vector of claim 13.

15. A method of editing a nucleobase of a DNA molecule, the method comprising contacting a DNA molecule with the cytidine base editor fusion protein of any one of claims 1-4 and converting a first nucleobase of the DNA molecule to a second nucleobase, with the proviso that, if the method is performed in vivo, the contacting is not made in a human ovum, a human totipotent cell, a human zygote, or a human embryo.

16. The method of claim 15, comprising one or more of:(a) the first nucleobase is cytosine and the second nucleobase is thymidine or the first nucleobase is adenine and the second nucleobase is guanine;(b) the method further comprises converting a third to a fourth nucleobase; and(c) the third nucleobase is guanine and the fourth nucleobase is adenine or the third nucleobase is thymine and the fourth nucleobase is cytosine.

17. The method of claim 15 or claim 16, comprising one or more of:(a) the cytidine base editor fusion protein deaminates the first nucleobase with lower spurious deamination in the DNA molecule as compared to the standard cytidine base editor fusion protein; and(b) the cytidine base editor fusion protein deaminates the first nucleobase at higher efficiency as compared to the standard cytidine base editor fusion protein.2020216484   05 Aug 202618. The method of any one of claims 15-17, comprising one or more of:(a) the contacting is performed in a cell;(b) the contacting is performed in a human cell or a non-human mammalian cell.

19. The method of any one of claims 15-18, wherein the contacting is in vivo or ex vivo.

20. A cytidine deaminase comprising an amino acid sequence that has at least 90% identity tothe amino acid sequenceMTSEKGPSTGDPTLRRRIESWEFDVFYDPRELRKETCLLYEIKWGMSRKIWRSSGKNTTNHVEV NFIKKFTSERRFHSSISCSITWFLSWSPCWECSQAIREFLSQHPGVTLVIYVARLFWHMDQRNR QGLRDLVNSGVTIQIMRASEYYHCWRNFVNYPPGDEAHWPQYPPLWMMLYALELHCIILSLPPC LKISRRWQNHLAFFRLHLQNCHYQTIPPHILLATGLIHPSVTWR and further comprises an alteration selected from the group consisting of R33A, K34A, R52A, and H122A,wherein a cytidine base editor fusion protein comprising the cytidine deaminase and a polynucleotide programmable DNA binding domain has an increased ratio of in cis to in trans activity (in cis:in trans) as compared to a standard cytidine base editor fusion protein comprising a rat APOBEC-1 cytidine deaminase (rAPOBEC-1) and a Cas9 nickase.

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