METHOD FOR PROCESSING NUCLEAR ACID SAMPLES

Description

BACKGROUND

[0001] A common technique used to study gene expression in living cells is to produce complementary deoxyribonucleic acid (cDNA) from a ribonucleic acid (RNA) molecule. This technique provides a means to study RNA from living cells which avoids the direct analysis of inherently unstable RNA. As a first step in cDNA synthesis, the RNA molecules from an organism are isolated from an extract of cells or tissues of the organism. After messenger RNA (mRNA) isolation, using methods such as affinity chromatography utilizing oligo dT (a short sequence of deoxy-thymidine nucleotides), oligonucleotide sequences are annealed to the isolated mRNA molecules and enzymes with reverse transcriptase activity can be utilized to produce cDNA copies of the RNA sequence, utilizing the RNA / DNA primer as a template. Thus, reverse transcription of mRNA is a key step in many forms of gene expression analyses. Generally, mRNA is reverse transcribed into cDNA for subsequent analysis by primer extension or polymerase chain reaction.

[0002] Reverse transcriptase has both an RNA-directed DNA polymerase activity and a DNA-directed DNA polymerase activity. The reverse transcription of RNA templates may require a primer sequence which is annealed to an RNA template in order for DNA synthesis to be initiated from the 3' OH of the primer. At room temperature, reverse transcriptase enzymes may allow formation of both perfectly matched as well as mismatched DNA / RNA hybrids. In some instances, a reverse transcriptase enzyme can produce large amounts of non-specific cDNA products as a result of such non-specific priming events. The products of non-specific reverse transcription can interfere with subsequent cDNA analyses, such as cDNA sequencing, real-time polymerase chain reaction (PCR), and alkaline agarose gel electrophoresis, among others. Non-specific cDNA templates produced by non-specific reverse transcriptase activity can present particular difficulties in applications such as real-time PCR. In particular, such non-specific cDNA products can give rise to false signals which can complicate the analysis of real-time PCR signals and products. Thus, the reduction of non-specific reverse transcriptase activity may result in greater specificity of cDNA synthesis. Currently, there are no reliable and easy to use methods for improving the specificity of reverse transcription. The methods of the present inventon satisfies these and other needs.

[0003] Several approaches may be used for obtaining transcriptome data from single cells. A pioneer approach used reverse transcriptase and oligo-dT primers with a T7 phage RNA polymerase promoter sequence attached to the 5' end of the oligo-dT run. The resulting cDNA was transcribed into multiple copies of RNA which were then converted back to cDNA (Phillips, et al., Methods 10(3):283-288 (1996)). This often truncates the cDNA molecule, losing 5' sequences of the original mRNA, especially for relatively long transcripts, and requires multiple rounds of processing when starting with low quantity (LQ) of cells, further exacerbating cDNA truncation. A recent modification (Hashimshony, et al., Cell Rep. 2(3):666-673 (2012)) enables multiplex analyses, but this is still 3' end sequence biased. Similarly, Kapteyn et al., BMC Genomics 11(1):413 (2010) and Picelli et al., Nature Protocols 9(1):171-181 (2014) disclose production of cDNAnucleic acids using a template switching oligonucleotide where only the 3' end ribonucleotides where only the 3' end comprises ribonucleotides. Other methods are based on PCR amplification of cDNA (Liu, et al., Methods Enzymol. 303:45-55 (1999), Ozsolak, et al., Genome Res. 20(4):519-525 (2010), Gonzalez, et al., PLoS ONE. 5(12):e14418 (2010), Kanamori, et al., Genome Res. 21(7):1150-1159 (2011), Islam, et al., Genome Res. 21(7):1160-1167 (2011), Tang, et al., Nat. Methods. 6(5):377-382 (2009), Kurimoto, et al., Nucleic Acids Res. 34(5):e42 (2006), Qiu S, et al., Front Genet. 3:124 (2012)). Furthermore, Jamburuthugoda et al., Nucleic Acids Res. 42(13):8405-8415 (2014) and Bibillo et al., J. Biol. Chem. 279:14945-14953 (2004) use acceptor RNA templates to characterize template jumping with Bombyx mori R2 reverse transcriptase.

[0004] These approaches, however, may yield biased representations of sequences along the mRNA, and fail to give complete sequences for mRNAs (e.g., long mRNAs) because DNA templates (e.g., long DNA templates) are discriminated against even when a long PCR reaction is used.SUMMARY

[0005] The present invention provides methods of amplifying cDNA from RNA isolated from low quantities of cells and / or single cells.

[0006] In particular, the present inventin relates to a method for preparing a complementary deoxyribonucleic acid (cDNA) molecule library comprising: (a) annealing one or more primers to a template nucleic acid molecules, thereby generating one or more annealed template nucleic acid molecules; and (b) mixing, in the presence of nucleotides, i. said one or more annealed template nucleic acid molecules; ii. one or more RNA template acceptor nucleic acid molecules; and iii. a modified reverse transcriptase derived from Bombyx mori, wherein said modified reverse transcriptase generates a plurality of continuous complementary deoxyribonucleic acid molecules by reverse transcribing a sequence of said annealed template nucleic acid molecule, migrating to an acceptor nucleic acid molecule; and reverse transcribing a sequence of said acceptor nucleic acid molecule without thermal cycling in a single reaction vessel.

[0007] In some embodiments, the modified reverse transcriptase comprises at least one improved enzyme property relative to a wild type unmodified reverse transcriptase, said improved enzyme property being selected from: higher thermo-stability, higher specific activity, higher processivity, higher strand displacement, higher end-to-end template jumping, higher affinity, and higher fidelity relative to said wild type unmodified reverse transcriptase. In some embodiments, modified reverse transcriptase is an R2 reverse transcriptase. In some embodiments, the modified reverse transcriptase has at least about 90% identity to SEQ ID NO: 49, SEQ ID NO: 50, SEQ ID NO: 51, SEQ ID NO: 52, SEQ ID NO: 53, SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56, SEQ ID NO: 57, SEQ ID NO: 58, SEQ ID NO: 59, SEQ ID NO: 60, SEQ ID NO: 61, SEQ ID NO: 62, SEQ ID NO: 63, SEQ ID NO: 64, SEQ ID NO: 65, SEQ ID NO: 66, or SEQ ID NO: 67, and contains at least one substitution modification relative to SEQ ID NO: 52.

[0008] In some embodiments, the method further comprises adding a tag to the template nucleic acid molecule, thereby generating a plurality of tagged continuous complementary deoxyribonucleic acid molecules after performing (a) and (b). In some embodiments, the method further comprises sequencing the tagged plurality of continuous complementary deoxyribonucleic acid molecules. In some embodiments, modified reverse transcriptase further comprises a tag, the tag being selected from biotin, azido group, acetylene group, His-tag, calmodulin-tag, CBP, CYD, Strep II, FLAG-tag, HA-tag, Myc-tag, S-tag, SBP-tag, Softag-1, Softag-3, V5-tag, Xpress-tag, isopeptag, SpyTag B, HPC peptide tags, GST, MBP, biotin carboxyl carrier protein, glutathione-S-transferase-tag, green fluorescent protein-tag, maltose binding protein-tag, Nus-tag, Strep-tag, and thioredoxin-tag.

[0009] In some embodiments, the one or more acceptor nucleic acid molecules comprise a modified nucleotide that stops the reverse transcription by the modified reverse transcriptase. In some embodiments, the method further comprises obtaining a sample from a subject, said sample comprising one or more cell free nucleic acids, and the method further comprises performing the reaction of (a) and (b) in the same vessel.

[0010] In some embodiments, the method further comprises depleting at least one ribosomal RNA (rRNA) from the sample comprising one or more template nucleic acid molecules prior to annealing one or more primers, optionally the step of depleting the at least one ribosomal RNA (rRNA) comprises hybridization of an oligonucleotide to the rRNA, or optionally the step of depleting said at least one ribosomal RNA (rRNA) comprises an oligonucleotide probe-guided endonucleolitic cleavage of the rRNA. In some embodiments, the one or more template nucleic acid molecules comprise at least one transfer RNA (tRNA) and the method further comprises depleting the at least one tRNA from the one or more template nucleic acid molecules prior to annealing one or more primers. In some embodiments, the method is performed in the absence of purification of one or more annealed template nucleic acid molecules. In some embodiments, the method further comprises purifying the mixture comprising a plurality of continuous complementary deoxyribonucleic acid molecule, optionally said purifying comprises two purification steps, and optionally the two purification steps comprise a nickel and a heparin affinity purification step.

[0011] The present invention provides an efficient and simple methods for cDNA and nucleic acid library preparation (e.g., single cell and / or bulk library preparation) that is compatible with various sequence technologies; high quality library preparation that can be used for single cell nucleic acid (e.g., RNA) sequencing and bulk nucleic acid (e.g., RNA) sequencing; modified reverse transcriptase enzymes with improved enzyme property; high conversion (e.g., efficiency and / or fidelity) of a nucleic acid sample (e.g., RNA, and / or mRNA, and / or DNA) to nucleic acid (e.g., cDNA) library; low non-specific products yield; and transcriptome analysis where cells don't go through stress (e.g., no need for elevated temperature for cDNA synthesis) because nucleic acid synthesis may be performed at ambient temperatures (e.g., 30 °C).

[0012] Advantages of the methods of the present invention also include their ability to produce a nucleic acid (e.g., cDNA) library using random or multi-priming and / or a library from fragmented / degraded nucleic acid molecule(s) (e.g., RNA and DNA), even at low amounts (e.g., 500 femtomolar) of fragmented / degraded nucleic acid molecule(s). Advantages of the methods of the present invention also include their ability (e.g., by using a modified reverse transcriptase) to amplify a fragment (e.g., amplification of the full fragment) and generate multiple copies of the full fragment for sequencing. Current available methods may cause a fragment to be amplified at a random location and may only amplify sections of the fragment, thus sequencing and identification of the fragment(s) according to current methods is not available at low amounts. Advantages of the methods of the present invention also include the amplification via a single step or via a two-step amplification protocol, thus increasing specificity and efficiency. Current methods include multiple step amplification that can result in low yield, low efficiency, and / or low specificity. Another adavantage of the methods of the present invention is their capability to prime using a piece of nucleic acid molecule (e.g., RNA) that does not have to be complementary to a template. Another advantage of the methods of the present invention is the ability of the modified enzymes to template jump at room temperature and / or at temperatures as low as about 30 °C. Another advantage of the methods of the present invention is their ability to prepare a library from a sample in less than three steps (Figure 1) and / or less than 4 h. This advantage is particular important for clinical research and testing and the medical field. Another advantage of the methods of the present invention is their ability (e.g., by using a modified reverse transcriptase) to improve template jumping, processivity, strand displacement properties, enzyme activity, and / or fidelity.

[0013] Additional advantages of the methods of the present invention will become readily apparent to those skilled in this art from the following detailed description. Accordingly, the drawings and description are to be regarded as illustrative in nature.BRIEF DESCRIPTION OF THE DRAWINGS

[0014] The novel features of the methods of the present invention are set forth in the appended claims. A better understanding of the features and advantages of the methods of the present invention will be obtained by reference to the following detailed description that sets forth illustrative embodiments, in which the principles of the disclosure are utilized, and the accompanying drawings (also "Figure" and "FIG." herein), of which: Figure 1 illustrates a difference between preparing a complementary deoxyribonucleic acid (cDNA) library between a traditional method and the method of the present invention and the methods not falling within the scope of the claims (hereinafter commonly referred to as "method(s) described herein"). Figure 1 also illustrates a difference between preparing a sample for sequencing from a liquid biopsy sample based on a traditional method and the methods described herein. The traditional method involves a protocol that requires about 1 to 2 d and more than 4-5 h of hands-on time, while the methods described herein involve a protocol that requires less than about 2 h and less than about 30 min of hands-on time; Figure 2 illustrates a workflow for constructing a library based on the methods described herein; Figure 3 illustrates a workflow for constructing a library; Figure 4 illustrates a workflow using random primers for constructing a library; Figure 5A illustrates a workflow using fragmented or degraded ribonucleic acid (RNA) or deoxyribonucleic acid (DNA) with RNA priming for constructing a library; Figure 5B illustrates an example of a workflow using fragmented or degraded RNA or DNA with RNA priming for constructing a library - method with specific primer; Figure 6A illustrates a workflow using fragmented or degraded RNA or DNA with a donor complex for constructing a library; Figure 6B illustrates an example of a workflow using fragmented or degraded RNA or DNA with a donor complex for constructing a library - with specific primer; Figure 7 illustrates a schematic representation of an N-terminal and a C-terminal truncation of an R2 reverse transcriptase; Figure 8 illustrates a sequence analysis with selected non-long terminal repeat (LTR) retrotransposon and an example of a site of N-truncation upstream two conservative regions (region -1 and region 0); Figure 9 illustrates a sequence analysis with selected non-LTR retrotransposon and an example of a site of C-terminal truncation downstream two conservative motifs 8* and 9*; Figure 10 illustrates a gel showing purified wild type R2 reverse transcriptase and N-terminal truncated R2 reverse transcriptase; Figure 11 illustrates a polyacrylamide gel electrophoresis (PAGE) gel showing activity and template jumping properties of an R2 enzyme and of moloney murine leukemia virus (MMLV) reverse transcriptase by using synthetic RNA; Figure 12A illustrates a workflow for sequencing library preparation; Figure 12B illustrates real-time PCR data of library preparation based on 1-pot (e.g., single vessel) reactions; Figure 12C illustrates a gel showing amplicon; Figure 13 illustrates 1-pot (e.g., single vessel) RNA library preparation using different template amounts; Figure 14 illustrates1-pot (e.g., single vessel) RNA library preparation with different template lengths; Figure 15 illustrates that enzyme activity and template jumping is dependent on the concentration of sodium chloride (NaCl); Figure 16A illustrates enzyme activity after nickel and / or heparin affinity purification visualized based on fluorescently labeled primer (fluorescein); Figure 16B illustrates template jumping properties after nickel and / or heparin affinity purification visualized based on Sybr gold staining; Figure 17 illustrates R2 enzyme activity and template jumping in the presence of DNA template (lane 1: no enzyme control; lane 2: 0.023 µg / µl enzyme in the presence of DNA template); Figure 18A illustrates a workflow of a method described herein for sequencing a library preparation from liquid biopsy; Figure 18B illustrates that a sample DNA fragment was captured by an R2 enzyme with both an RNA priming approach and an RNA donor approach; Figure 18C illustrates that a sample DNA fragment (at various concentrations) was captured by an R2 enzyme using an RNA priming approach; Figure 18D illustrates that a sample DNA fragment (at various concentrations) was captured by an R2 enzyme using an RNA donor approach; Figure 19 illustrates that a sample DNA fragment was captured using an RNA donor approach at a concentration as low as 500 femtomolar; Figure 20 illustrates that the method described herein can be used for liquid biopsy application. Figure 20 discloses that the methods described herein show high sensitivity compared to current available technology (e.g., the methods describeed herein can be used for very low DNA amounts, as low as 0.3 pg, which is about a 100-1000 fold higher sensitivity than current available methods). Data also shows the potential for applications involving DNA amounts that are even lower than 0.3 pg (e.g., a few orders of magnitude lower); Figure 21 illustrates a method described herein that takes advantage of detecting mutations on both RNA (e.g., exosomal RNA) and cell-free DNA. This method can be used to detect rare mutations or low frequency mutations (e.g., some mutated alleles can occur at less than 1 copy per mL of plasma) by increasing the detection sensitivity by combining RNA and cell-free DNA. This method can be used, for example, to test analytes isolated from body fluids (e.g., blood). Body fluids, such as blood plasma, may contain different cell-free sources of nucleic acids. Such cell-free sources can be circulating cell-free DNA (e.g., double-stranded DNA (dsDNA) and single-stranded DNA (ssDNA)) and RNA (e.g., extracellular RNA (exRNA) and RNA from exosomes). Cell-free DNA can be present at various stages of fragmentation and / or degradation (e.g., different lengths). Extracellular RNA can include, but is not limited to, messenger RNA (mRNA), transfer RNA (tRNA), microRNA (miRNA), small interfering RNA (siRNA), and long non-coding RNA (lncRNA). Figure 21 also illustrates a method described herein that driscriminately tag cell-free DNA and RNA present in the same, or different, tube (e.g., same PCR tube). Tagging facilitates post-sequencing analysis by allowing discrimination between sequences that originated from DNA and RNA templates. Figure 21 shows that two different analytes, DNA and RNA, were polytailed in the presence of Terminal Deoxynucleotidyl Transferase (TdT), Poly A Polymerase, and specific nucleotide substrates dCTP (or alternatively dGTP or dTTP) and ATP. In short, a reaction containing both RNA and DNA (dsDNA and ssDNA) was mixed and incubated with poly A polymerase, TdT, dCTP, and ATP (Figure 21). Poly A polymerase preferentially extends RNA using the preferred substrate ATP while TdT preferentially extends DNA using the preferred deoxy substrate dCTP. In general, the reaction can be performed with both enzymes (e.g., poly A polymerase and TdT) at the same time, or alternatively, it can be performed sequentially with one enzyme at a time; Figure 22A illustrates that streptavidin-immobilized oligonucleotides can be used for improving the efficiency of specific template capture and template jumping capabilities. Figure 22A shows that streptavidin-immobilized oligonucleotides bind to specific DNA and / or RNA template(s). In this case, the streptavidin-immobilized oligonucleotides are bound to magnetic beads. Once the specific DNA and / or RNA template is bound to the streptavidin-magnetic bead complex, the template can be enriched. The oligonucleotide can be used as a primer and the template can be transcribed in the presence of an enzyme (e.g., R2 enzyme); Figure 22B illustrates that a complex comprising of streptavidin bound to both an oligonucleotide primer and an oligonucleotide acceptor is capable of binding to specific DNA and / or RNA template(s). In short, the specific template binds to the oligonucleotide primer, which can then be extended in the presence of an enzyme (e.g., R2 enzyme). The primer extension then undergoes template jumping due to the close proximity between the acceptor oligonucleotide and the specific template; Figure 22C illustrates that a complex comprising of streptavidin bound to an oligonucleotide primer, an oligonucleotide acceptor, and a magnetic bead is capable of binding to specific DNA and / or RNA template(s). In this case, the specific template is first enriched with magnetic beads. The template is then copied in the presence of an enzyme (e.g., R2 enzyme) and the extended sequence can further undergo template jumping; Figures 23A and 23B illustrate template concatemerization. Some sequencing technologies have a long sequencing read-length (~500bp to ~50000bp) while others have a short sequencing read-length (~50bp to ~250bp). Most of the isolated cell-free DNA and RNA from body fluids are short fragments (~20bp to ~200bp). The method shown in Figures 23A and 23B is particularly suitable for sequencing technologies that have a long sequencing read-length because the method is capable of forming long template concatemers. Figure 23A illustrates a method of concatemerizing several templates separated by signaling sequences. In this method, short dsDNA fragments are converted to a long concatemer separated by signaling sequences. Figure 23B shows a final product of a concatemerization that includes specific adaptors on both ends. The adaptor design incorporates unique molecular identifier sequences (UMI) that allow one to trace the tagged molecule and also help reduce errors during data analysis. In short, dsDNA fragments are ligated with two or more adaptors. The ligated fragments are then extended using PCR without primers (alternatively isothermal amplification). The concatemer length or the number of attached templates can be determined, for example, by tagging the adaptors with modified nucleotides (e.g., by introducing methylated nucleotides or by inserting dUTP). The length of the concatemer can be regulated based on the ratio between modified / unmodified adaptors. The adaptor sequences can serve as a homology priming location (annealed to the homology spot ssDNA fragments serve as template and primer). The reaction in the PCR undergoes a selected number of cycles (the more cycles, the longer the concatemer) or time (isothermal amplification). The reaction is then stopped and the long dsDNA concatemers are ligated with two unique dsDNA adaptors. See also, Example 13; Figure 24A illustrates a workflow of template concatemerization; Figure 24B illustrates a gel showing the concatemerization of a 200bp DNA fragment; Figure 25 illustrates a schematic reaction in the presence of a reverse transcriptase and a second enzyme or enzymatic activity (i.e., companion enzyme), such as an ssDNA 3' to 5' exonuclease or a polymerase with editing activity (e.g., 3' to 5' exonuclease). Examples of a companion enzyme include T4 DNA polymerase, exonuclease I, and exonuclease T. One function or purpose of the companion enzyme is to remove the excess of free unused extension primer. Free primer may contribute to unwanted products (e.g., free primer may serve as a jumping acceptor or it may be used as a nonspecific primer). Figure 25 shows a reaction scheme which starts with the annealing of a primer to an RNA template (the primer can be annealed to a specific sequence, or to a polyA tail, or to a product of poly-tailing of the 3' end). The reaction is then mixed with an enzyme (e.g., R2 enzyme), a polymerase with editing activity (e.g., 3' to 5' exonuclease), and an acceptor template (e.g., acceptor template with a protected 3' end). The acceptor template may include bases at the 3' end to protect it against exo digestion. Examples of nucleotides that can be used to protect the acceptor template include ribonucleotides, thiophosphates, and nucleotide bases with or without modification. Alternatively, the reaction shown in Figure 25 can be executed in a single step if, for example, a proper ratio of primer to exonuclease is used. As shown in Figure 25, if the R2 reverse transcriptase dissociates from the DNA / RNA heteroduplex before completion of the jumping to the acceptor template, the product is overextended (3' overhang). The 3' to 5' exonuclease activity can then regenerate the bland end structure of the DNA / RNA duplex. In general, jumping to the acceptor template can be completed by a multi-turnover mechanism, thus increasing the yield of the reaction; Figure 26 illustrates a BioAnalyzer trace data of Next-Generation Sequencing (NGS) libraries. Line 1 represents a fragmented RNA seq library from plasma and line 2 represents a no-fragmented RNA seq library from plasma (see, Example 15); Figure 27 and Figure 28 illustrate methods of generating cell free deoxyribonucleic acid (cfDNA) library; Figure 29 illustrates library preparation: pulling ribosomal RNA and / or transfer RNA and / or PCR products using complementary oligonucleotide attached to magnetic beads or solid support to maximize sequencing capacity; Figure 30 illustrates library preparation: oligonucleotide-guided degradation of ribosomal RNA and / or transfer RNA and / or PCR products to maximize sequencing capacity. Figure 31 illustrates a technology described herein that is capable of capturing / targeting all species of RNA simultaneously. Figure 31 shows cell free RNA library that was obtained according to the methods described herein. The graph corresponds to Illumina sequencing results of library prepared from 20 ng cell free RNA (cfRNA). 28357171 reads were analyzed, 91.9% mapped. Examples of captured items / analytes included, but was not limited to, vault RNA, tRNA, srpRNA, sRNA, snRNA, snoRNA, scRNA, scaRNA, rRNA, RNA, long non-coding RNAs (lncRNAs), micro RNA (miRNA), macro lnc RNA, miscellaneous RNA, 3 prime overlapping ncRNA, DNA, bidirectional promoter incRNA, lincRNA, MT_tRNA, MT_rRNA, ribozyme, LTR, retroposon, and SINE. DETAILED DESCRIPTION

[0015] While various embodiments of the invention been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. It should be understood that various alternatives to the embodiments described herein may be employed.

[0016] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In case of conflict, the present application including the definitions will control. Also, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular. In order to further define the present invention, the following terms, abbreviations and definitions are provided.

[0017] As used herein, the term "about" refers to variations in the numerical quantity that may occur, for example, through typical measuring and liquid handling procedures used for making concentrates or solutions in the real world; through inadvertent error in these procedures; through differences in the manufacture, source, or purity of the ingredients employed to make the compositions or to carry out the methods; and the like. The term "about" also encompasses amounts that differ due to different equilibrium conditions for a composition resulting from a particular initial mixture. Whether or not modified by the term "about", the claims include equivalents to the quantities. In some embodiments, the term "about" means within 10% of the reported numerical value, or within 5% of the reported numerical value, or within 20% of the reported numerical value.

[0018] The indefinite articles "a" and "an" preceding an element or component of the methods described herein are intended to be nonrestrictive regarding the number of instances, i.e., occurrences of the element or component. Therefore "a" or "an" should be read to include one or at least one, and the singular word form of the element or component also includes the plural unless the number is obviously meant to be singular.

[0019] The terms "anneal", "hybridize" or "bind," can be used interchangeably herein to refer to the combining of one or more single-stranded polynucleotide sequences, segments or strands, and allowing them to form a double-stranded molecule through base pairing. Two complementary sequences (e.g., ribonucleic acid (RNA) and / or deoxyribonucleic acid (DNA)) can anneal or hybridize by forming hydrogen bonds with complementary bases to produce a double-stranded polynucleotide or a double-stranded region of a polynucleotide.

[0020] The term "subject" can be any animal which may benefit from the methods of the disclosure, including, e.g., humans and non-human mammals, such as primates, rodents, horses, dogs and cats. Subjects include a eukaryotic organism, a mammal such as a primate, e.g., chimpanzee or human, cow; dog; cat; a rodent, e.g., guinea pig, rat, mouse; rabbit; or a bird; reptile; or fish. Subjects specifically intended for treatment using the methods described herein include humans. A subject may be an individual or a patient.

[0021] As used herein, the term "primer extension reaction" generally refers to the denaturing of a double-stranded nucleic acid, binding of a primer to one or both strands of the denatured nucleic acid, followed by elongation of the primer(s).

[0022] As used herein, the term "reaction mixture" generally refers to a composition comprising reagents necessary to complete nucleic acid amplification (e.g., DNA amplification, RNA amplification), with examples of such reagents that include primer sets having specificity for target RNA or target DNA, DNA produced from reverse transcription of RNA, a DNA polymerase, a reverse transcriptase (e.g., for reverse transcription of RNA), suitable buffers (including zwitterionic buffers), co-factors (e.g., divalent and monovalent cations), dNTPs, and other enzymes (e.g., uracil-DNA glycosylase (UNG))). In some cases, reaction mixtures can also comprise one or more reporter agents.

[0023] As used herein, a "reporter agent" generally refers to a composition that yields a detectable signal, the presence or absence of which can be used to detect the presence of amplified product.

[0024] As used herein, the term "target nucleic acid" generally refers to a nucleic acid molecule in a starting population of nucleic acid molecules having a nucleotide sequence whose presence, amount, and / or sequence, or changes in one or more of these, are desired to be determined. A target nucleic acid may be any type of nucleic acid, including DNA, RNA, and analogues thereof.

[0025] The term "primer", as used herein, refers to an oligonucleotide, occurring naturally as in a purified restriction digest or produced synthetically that is characterized by an ability to be extended against a template oligonucleotide, so that an oligonucleotide whose sequence is complementary to that of at least a portion of the template molecule is linked to the primer, when all are placed in the presence of nucleotides at a suitable temperature and pH. However, the mere ability to be used in this fashion does not require that primers be fully extended against a template, and in some embodiments, primers are used only as a site for the addition of a small number of non-templated nucleotides. Primers such as primer hexamers having a length of at least 6 nucleotides long can be used. In some embodiments, a primer may be fluorescently labeled (e.g., 5'- / 56FAM / TGATGACGAGGCATTTGGC / 3'). In some embodiments, primers have a length within the range of about 6 to about 100 nucleotides, or in some embodiments from about 10 to about 70 nucleotides. In some embodiments, larger primers can be used. In some embodiments, random primers may be used. In some embodiments, a primer may be a random primer. In some embodiments, one or more primer(s) may be one or more random primer(s).

[0026] The term "one or more primer(s)" can comprise any number of primers or random primers. For example, "one or more primer(s)" can include at least, at most, or about 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, 20, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, or 100 primers or random primers. One or more primer(s) can include about 1 to about 2, about 1 to about 3, about 1 to about 4, about 1 to about 5, about 1 to about 6, about 1 to about 7, about 1 to about 8, about 1 to about 9, about 1 to about 10, about 1 to about 15, about 1 to about 20, about 1 to about 25, about 1 to about 30, about 1 to about 35, about 5 to about 15, about 3 to about 10, about 5 to about 20, about 10 to about 50, about 30 to about 100, or more than about 100 primers. One or more primer(s) can comprise any number of primers. For example, one or more primer(s) can include at least, at most, or about 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, 20, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 86, 87, 88, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99, 100, 150, 200, 250, 300, 350, 400, 450, 500, 550, 600, 700, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10000, 11000, 12000, 13000, 14000, 15000, 16000, 17000, 18000, 19000, 20000, 25000, 30000, 35000, 40000, 45000, 50000, 55000, 60000, 65000, 70000, 75000, 80000, 85000, 90000, 95000, 100000, 150000, 200000, 250000, 300000, 350000, 400000, 450000, 500000, 550000, 600000, 650000, 700000, 750000, 800000, 850000, 900000, 950000, 1000000, 1500000, 2000000, 2500000, 3000000, 3500000, 4000000, 4500000, 5000000, 5500000, 6000000, 6500000, 7000000, 7500000, 8000000, 8500000, 9000000, 9500000, or 10000000 primers. One or more primer(s) can include about 10 to about 100, about 100 to about 1000, about 1000 to about 10,000, about 10,000 to about 100,000, about 100,000 to about 1,000,000, or about 1,000,000 to about 10,000,000 primers.

[0027] The term "random primer," as used herein, refers to a primer containing a random base sequence therein, and is intended to encompass primers whether they consist partially or wholly of random base sequences.

[0028] In some embodiments, a primer may comprise an adaptor sequence. In some embodiments, the 5' tail sequence of a primer comprises a sequence which does not hybridize to a target (the adaptor sequence). The adaptor sequence may be selected such that it is the same in a variety of primers which have different 3' target binding sequences (i.e., a "universal" 5' tail sequence). This allows a single reporter probe sequence to be used for detection of any desired target sequence, which is an advantage in that synthesis of the reporter probe is more complex due to the labeling. In some embodiments, a primer may comprise an RNA primer. In some embodiments, a primer may comprise a DNA primer. In some embodiments, a primer may comprise an R2 RNA primer. In some embodiments, a primer may comprise one or more random primer(s).

[0029] As used herein, the tem "acceptor template" is synonymous to "acceptor nucleic acid molecule." In some embodiments, an acceptor nucleci acid may be modified. In some embodiments, an acceptor nucleic acid molecule may be modified at the 3' end, for example to protect it from being mistaken as an RNA primer. In some embodiments, the modification of the acceptor nucleic acid molecule may comprise a dideoxy 3' end. In some embodiments, the modification may comprise a phosphorylated 3' end. In some embodiments, the phosphorylated 3' end of a polynucleotide or of an acceptor nucleic acid molecule, which typically has a hydroxyl group on its 3' end, can act as a 3' block because extension by an enzyme of the methods described herein, or of DNA polymerase for example may be inhibited or ligation by a ligase may be inhibited. Another example of a 3' block includes the addition of a 3' C3 spacer (three-carbon spacer) to the 3' end of a polynucleotide which can function as an effective blocking agent against polymerase extension. Zhou, et al., Clin. Chem., 50: 1328-1335 (2004). Thus, the 3' end can be blocked by the addition of, for example, a C3 spacer, a phosphate, an amine group (NH2), or any other chemical modification that inhibits formation of a subsequent phosphodiester bond between the 3' end of the polynucleotide and another nucleotide.

[0030] An "overhang sequence," as used herein, refers to a single stranded region of nucleic acid extending from a double stranded region.

[0031] An "isolated" polynucleotide, as used herein, means a polynucleotide that has been either removed from its natural environment, produced using recombinant techniques, or chemically or enzymatically synthesized. A polynucleotide can also be purified, i.e., essentially free from any other polynucleotides and associated cellular products or other impurities.

[0032] The term "polymerase" as used herein can refer to an enzyme that links individual nucleotides together into a strand, using another strand as a template. In some embodiments, the polymerase is a polymerase with editing capabilities. In some embodiments, the polymerase with editing capabilities may be 3' to 5' exonuclease, T4 DNA polymerase, exonuclease I, Phi29, Pfu, Vent, KOD, exonuclease III, and exonuclease T. Examples of polymerases can include a DNA polymerase, an RNA polymerase, an RNA-directed DNA polymerase, reverse transcriptase, a polypeptide having reverse transcriptase activity, or any variant thereof, a thermostable polymerase, a wild-type polymerase, a modified polymerase, E. coli DNA polymerase I, T7 DNA polymerase, bacteriophage T4 DNA polymerase PHI 29 (phi29) DNA polymerase, Taq polymerase, Tth polymerase, Tli polymerase, Pfu polymerase VENT polymerase, DEEPVENT polymerase, EX-Taq polymerase, LA-Taq polymerase, Sso polymerase, Poc polymerase, Pab polymerase, Mth polymerase, ES4 polymerase, Tru polymerase, Tac polymerase, Tne polymerase, Tma polymerase, Tca polymerase, Tih polymerase, Tfi polymerase, Platinum Taq polymerases, Tbr polymerase, Tfl polymerase, Tth polymerase, Pfutubo polymerase, Pyrobest polymerase, Pwo polymerase, KOD polymerase, Bst polymerase, Sac polymerase, Klenow fragment, polymerase with 3' to 5' exonuclease activity, and variants, modified products and derivatives thereof. In some embodiments, the polymerase may be a reverse transcriptase or a modified reverse transcriptase, or the polymerase may be a single subunit polymerase. The polymerase can have high processivity, namely the capability of the polymerase to consecutively incorporate nucleotides into a nucleic acid template without releasing the nucleic acid template.

[0033] The term "reverse transcriptase" or RT refers to an enzyme with both an RNA-directed DNA polymerase and a DNA-directed DNA polymerase. RT refers to a group of enzymes having reverse transcriptase activity (e.g., that catalyze synthesis of DNA from an RNA template). In general, such enzymes include retroviral reverse transcriptase, retrotransposon reverse transcriptase, retroplasmid reverse transcriptases, retron reverse transcriptases, bacterial reverse transcriptases, group II intron-derived reverse transcriptase, and mutants, variants or derivatives thereof. Non-retroviral reverse transcriptases include non-long terminal repeat (LTR) retrotransposon reverse transcriptases, retroplasmid reverse transcriptases, retron reverse transciptases, and group II intron reverse transcriptases. Further bacterial reverse transcriptases are described by Simon D & Zimmerly S (2008) "A diversity of uncharacterized retroelements in bacteria" Nucleic Acids Res 36(22):7219-7229., and Kojima, KK & Kanehisa, M (2008) "Systematic survey for novel types of prokaryotic retroelements based on gene neighborhood and protein architecture" Mol Biol Evol 25:1395- 1404., which describe many classes of non-retroviral reverse transcriptases (i.e., retrons, group II introns, and diversity-generating retroelements among others). Reverse transcriptase has been used primarily to transcribe RNA into cDNA, which can then be cloned into a vector for further manipulation or used in various amplification methods such as polymerase chain reaction, nucleic acid sequence-based amplification (NASBA), transcription mediated amplification (TMA), self-sustained sequence replication (3SR), diverse primer extension reactions, 5'RACE, detection of chemical modifications or other techniques that require synthesis of DNA using an RNA template.Retroviral Reverse Transcriptase Enzymes

[0034] Moloney Murine Leukemia Virus (M-MLV) reverse transcriptase contains a single subunit of 78 kDa with RNA-dependent DNA polymerase and RNase H activity. This enzyme has been cloned and expressed in a fully active form in E. coli (reviewed in Prasad, V. R., Reverse Transcriptase, Cold Spring Harbor, N.Y.: Cold Spring Harbor Laboratory Press, p. 135 (1993)).

[0035] Human Immunodeficiency Virus (HIV) reverse transcriptase is a heterodimer of p66 and p51 subunits in which the smaller subunit is derived from the larger subunit by proteolytic cleavage. The p66 subunit has both a RNA-dependent DNA polymerase and an RNase H domain, while the p51 subunit has only a DNA polymerase domain. Active HIV p66 / p51 reverse transcriptase has also been cloned and expressed successfully in a number of expression hosts, including E. coli (reviewed in Le Grice, S. F. J., Reverse Transcriptase, Cold Spring Harbor, N.Y.: Cold Spring Harbor Laboratory press, p. 163 (1993)). Within the HIV p66 / p51 heterodimer, the 51-kD subunit is catalytically inactive, and the 66-kD subunit has both DNA polymerase and RNase H activity (Le Grice, S. F. J., et al., EMBO Journal 10:3905 (1991); Hostomsky, Z., et al., J. Virol. 66:3179 (1992)).

[0036] Members of the Avian Sarcoma-Leukosis Virus (ASLV) reverse transcriptase family are also a heterodimers of two subunits, alpha (approximately 62 kDa) and beta (approximately 94 kDa), in which the alpha subunit is derived from the beta subunit by proteolytic cleavage (reviewed in Prasad, V. R., Reverse Transcriptase, Cold Spring Harbor, N.Y.: Cold Spring Harbor Laboratory Press (1993), p. 135). Members of this family include Rous Sarcoma Virus (RSV) reverse transcriptase, Avian Myeloblastosis Virus (AMV) reverse transcriptase, Avian Erythroblastosis Virus (AEV) Helper Virus MCAV reverse transcriptase, Avian Myelocytomatosis Virus MC29 Helper Virus MCAV reverse transcriptase, Avian Reticuloendotheliosis Virus (REV-T) Helper Virus REV-A reverse transcriptase, Avian Sarcoma Virus UR2Helper Virus UR2AV reverse transcriptase, Avian Sarcoma Virus Y73 Helper Virus YAV reverse transcriptase, Rous Associated Virus (RAV) reverse transcriptase, and Myeloblastosis Associated Virus (MAV) reverse transcriptase.

[0037] ASLV reverse transcriptase can exist in two additional catalytically active structural forms, Ad and a (Hizi, A. and Joklik, W. K., J. Biol. Chem. 252: 2281 (1977)).

[0038] Sedimentation analysis suggests the presence of alpha / beta and beta / beta are dimers and that the a form exists in an equilibrium between monomeric and dimeric forms (Grandgenett, D. P., et al., Proc. Nat. Acad. Sci. USA 70:230 (1973); Hizi, A. and Joklik, W. K., J. Biol. Chem. 252:2281 (1977); and Soltis, D. A. and Skalka, A. M., Proc. Nat. Acad. Sci. USA 85:3372 (1988)). The ASLV alpha / beta and beta / beta reverse transcriptases are the only known examples of retroviral reverse transcriptase that include three different activities in the same protein complex: DNA polymerase, RNase H, and DNA endonuclease (integrase) activities (reviewed in Skalka, A. M., Reverse Transcriptase, Cold Spring Harbor, N.Y.: Cold Spring Harbor Laboratory Press (1993), p. 193). The a form lacks the integrase domain and activity.

[0039] Various forms of the individual subunits of ASLV reverse transcriptase have been cloned and expressed. These include a 98-kDa precursor polypeptide that is normally processed proteolytically to beta and a 4 kDa polypeptide removed from the beta carboxy end (Alexander, F., et al., J. Virol. 61:534 (1987) and Anderson, D. et al., Focus 17:53 (1995)), and the mature beta subunit (Weis, J. H. and Salstrom, J. S., US Patent 4,663,290 (1987); and Soltis, D. A. and Skalka, A. M., Proc. Nat. Acad. Sci. USA 85:3372 (1988)). (See also Werner S, and Wohrl B. M., Eur. J. Biochem. 267:4740-4744 (2000); Werner S, and Wohrl B. M., J. Virol. 74:3245-3252 (2000); Werner S, and Wohrl B. M., J. Biol. Chem. 274:26329-26336 (1999).) Heterodimeric RSV alpha / beta reverse transcriptase has also been purified from E. coli cells expressing a cloned RSV beta gene (Chemov, A. P., et al., Biomed. Sci. 2:49 (1991)).Reverse Transcriptases of Non-Retroviral Origin

[0040] Reverse transcriptase enzymes may also be isolated from a large number of mobile genetic elements which are not of retroviral origin. Such mobile genetic elements are resident in the genomes of higher order species and play a function role in life cycle of these mobile genetic elements. Mobile genetic elements are known to encode genes for reverse transcriptase enzymes (reviewed in Howard M Temin, Reverse Transcription in the Eukaryotic Genome: Retroviruses. Pararetroviruses, Retrotransposons, and Retrotranscripts, Mol. Biol. Evol. 2(6):455-468). These elements include, but are not limited, to retrotransposons. Retrotransposons include the non-long terminal repeat (LTR) retrotransposon and LTR mobile elements (e.g., TY3, TY5, non-LTR, LINE-L1, R2, R1). (Reviewed by Cordaux and Batzer, Nature Reviews, October 2009, volume 10, pp 691-703.).

[0041] As used herein, "non-LTR retrotransposon" refers to naturally occurring proteins encoded by non-LTR retrotransposons and polypeptide fragments thereof which possess reverse transcriptase activity, as well as proteins or polypeptides derived therefrom which contain one or more amino acid substitutions that either enhance the reverse transcriptase activity thereof or have no deleterious effect thereon. A preferred class of non-LTR retrotransposon are R2 proteins or polypeptides. Thus, as used herein, "R2 protein or R2 enzyme or polypeptide or a functional fragment thereof" refers to naturally occurring proteins encoded by R2 elements and polypeptide fragments thereof which possess reverse transcriptase activity, as well as proteins or polypeptides derived therefrom which contain one or more amino acid substitutions that either enhance the reverse transcriptase activity thereof or have no deleterious effect thereon.

[0042] Retroelements, genetic elements that encode RTs, are divided into two major families denoted LTR-containing retroelements and non-LTR-containing retroelements (Xiong Y, Eickbush TH (1990) "Origin and evolution of retroelements based upon their reverse transcriptase sequences" EMBO J 9:3353-62). Non-LTR-retroelements are a diverse family of RT-encoding elements that includes retroplasmids, non-LTR-retrotransposons, retrons, and mobile group II introns.

[0043] As used herein, the term polymerase "active fraction" is defined as a fraction of enzyme with polymerase activity. For example, a reverse transcriptase active fraction (RT active fraction) is a fraction of enzyme that has a reverse transcriptase activity.

[0044] As used herein, the terms "variant," "modified," "non-naturally occurring," and "mutant" are synonymous and refer to a polypeptide or enzyme differing from a specifically recited polypeptide or enzyme by one or more amino acid insertions, deletions, mutations, and substitutions, created using, e.g., recombinant DNA techniques, such as mutagenesis. Guidance in determining which amino acid residues may be replaced, added, or deleted without abolishing activities of interest, may be found by comparing the sequence of the particular polypeptide with that of homologous polypeptides, e.g., yeast or bacterial, and minimizing the number of amino acid sequence changes made in regions of high homology (conserved regions) or by replacing amino acids with consensus sequences. In some embodiments, the terms "derivative," "variant," "modified," "non-naturally occurring," and "mutant" are used interchangeably.

[0045] The mutants referred to in the methods described herein may be generated in accordance with any suitable method, including methods described and exemplified herein. Mutations, such as substitutions, insertions, deletions, and / or side chain modifications, may be introduced into the nucleotide and amino acid sequences of the gene of interest using any suitable technique, including site-directed mutagenesis (Wu, ed., Meth. Enzymol. 217, Academic Press (1993)). The lambda red recombinase method may be used to "knock out" genes (Datsenko et al., PNAS USA 97: 6640-6645 (2000)). Permanent, marker-free, multiple gene disruptions may be created. Non-naturally occurring nucleotides and amino acids also may be used.

[0046] As used herein, "homologue" refers to a protein that is functionally equivalent i.e. has the same enzymatic activity as an enzyme having an amino acid sequence of the specified sequence identification number, but may have a limited number of amino acid substitutions, deletions, insertions or additions in the amino acid sequence. In order to maintain the function of the protein, the substitutions may be conservative substitutions, replacing an amino acid with one having similar properties.

[0047] In some embodiments, a homologue refers to a protein which has an identity of at least about 25%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 85%, at least about 90%, at least about 95% or at least about 99% with the amino acid sequence of SEQ ID NO corresponding to the protein. Algorithms for determining sequence identity include e.g. BLAST available through the National Center for Biotechnology Information (NCBI). Sequences may be determined to be similar to a degree that indicates homology and thus similar or identical function.

[0048] A polynucleotide encoding a homologue of each enzyme may be obtained by appropriately introducing substitution, deletion, insertion, and / or addition to the DNA of the enzyme which is composed of a nucleotide sequence described herein, using methods such as random mutagenesis and site-specific mutagenesis (Nucleic Acid Res. 10, pp. 6487 (1982), Methods in Enzymol. 100, pp. 448 (1983), Molecular Cloning 2nd Edt., Cold Spring Harbor Laboratory Press (1989), PCR A Practical Approach IRL Press pp. 200 (1991)). The polynucleotide encoding a homologue of each enzyme may be introduced and expressed in a host to obtain the homologue.

[0049] The term "heterologous" refers to a molecule or activity derived from a source other than the referenced species whereas "homologous" refers to a molecule or activity derived from the host microbial organism. Accordingly, exogenous expression of an encoding nucleic acid as described herein may use either or both a heterologous or homologous encoding nucleic acid.

[0050] In some embodiments, a host cell may be selected from, and the modified or non-naturally occurring enzyme generated in, for example, bacteria, yeast, fungus or any of a variety of other organisms may be used as a host organism.

[0051] In some embodiments, the host is not particularly restricted and the enzymatic activity or activities may be incorporated into any suitable host organism using methods, for example, as described herein. In some embodiments, the host is selected from bacteria, yeast, algae, cyanobacteria, fungi, or a plant cell, or any combination thereof. E. coli and S. cerevisiae are particularly useful host organisms since they are well characterized microorganisms suitable for genetic engineering.

[0052] As used herein, "enzyme" includes proteins produced by a cell capable of catalyzing biochemical reactions. Further, unless context dictates otherwise, as used herein "enzyme" includes protein fragments that retain the relevant catalytic activity, and may include artificial enzymes synthesized to retain the relevant catalytic activity.

[0053] Each of the enzymes described herein may be attached to an additional amino acid sequence as long as it retains an activity functionally equivalent to that of the enzyme. As mentioned above, it is understood that each enzyme or a homologue thereof may be a (poly)peptide fragment as long as it retains an activity functionally equivalent to that of the enzyme.

[0054] In some embodiments, the enzymes for use in the methods and kits described herein include any enzyme having reverse transcriptase activity. Such enzymes include non-retroviral reverse transcriptases, retroviral reverse transcriptases, retrotransposon reverse transcriptases, non-LTR retrotransposons, R2 reverse transcriptases, LTR-retrotransposons, hepatitis B reverse transcriptases, cauliflower mosaic virus reverse transcriptases, bacterial reverse transcriptases, Tth DNA polymerases, Taq DNA polymerases (Saiki, R. K., et al., Science 239:487-491 (1988); US Patents 4,889,818 and 4,965,188), Tne DNA polymerases (WO 96 / 10640), Tma DNA polymerases (US Patent 5,374,553) and mutants, fragments, variants or derivatives thereof. In some embodiments, reverse transcriptases for use in the methods described hereininclude retroviral reverse transcriptases such as M-MLV reverse transcriptase, AMV reverse transcriptase, RSV reverse transcriptase, RAV reverse transcriptase, MAV reverse transcriptase, and generally ASLV reverse transcriptases. Mutant reverse transcriptases can, for example, be obtained by mutating the gene or genes encoding the reverse transcriptase of interest by site-directed or random mutagenesis. Such mutations may include point mutations, deletion mutations, insertional mutations, and truncations. For example, one or more point mutations (e.g., substitution of one or more amino acids with one or more different amino acids) may be used to construct mutant reverse transcriptases for use in the methods described herein.

[0055] In some embodiments, the enzyme is selected and / or engineered to exhibit high fidelity with low error rates. The fidelity of a nucleotide polymerase is typically measured as the error rate, i.e., the frequency of incorporation of a nucleotide in a manner that violates the widely known Watson-Crick base pairing rules. The fidelity or error rate of a polymerase (e.g., DNA polymerase) may be measured using any suitable assay (see, for example, Lundburg et al., 1991 Gene, 108:1-6). The term "fidelity" can be used to refer to the accuracy of polymerization, or the ability of the polymerase to discriminate correct from incorrect substrates, (e. g., nucleotides) when synthesizing nucleic acid molecules (e. g. RNA or DNA) which are complementary to a template. The higher the fidelity of an enzyme, the less the enzyme misincorporates nucleotides in the growing strand during nucleic acid synthesis; that is, an increase or enhancement in fidelity results in a more faithful polymerase having decreased error rate (decreased misincorporation rate). In some embodiments, the misincorporation error rate is at most about 10-2, 10-4, 10-6, or 10-8.

[0056] In some embodiments, the non-naturally occurring or modified enzyme (e.g., non-naturally occurring or modified reverse transcriptase, non-naturally occurring or modified non-LTR retrotransposon, non-naturally occurring or modified R2 reverse transcriptase) or a modified polypeptide having reverse transcriptase activity exhibits a misincorporation error rate of equal to or less than about 50%, equal to or less than about 45%, equal to or less than about 40%, equal to or less than about 35%, equal to or less than about 30%, equal to or less than about 25%, equal to or less than about 20%, equal to or less than about 15%, equal to or less than about 10%, equal to or less than about 9%, equal to or less than about 8%, equal to or less than about 7%, equal to or less than about 6%, equal to or less than about 5%, equal to or less than about 4%, equal to or less than about 3%, equal to or less than about 2%, equal to or less than about 1%, equal to or less than about 0.01%, equal to or less than about 0.001%, equal to or less than about 0.0001%, equal to or less than about 0.00001%, equal to or less than about 0.000001%, or equal to or less than about 0.0000001%.

[0057] In some embodiments, the non-naturally occurring or modified enzyme (e.g., non-naturally occurring or modified reverse transcriptase, non-naturally occurring or modified non-LTR retrotransposon, non-naturally occurring or modified R2 reverse transcriptase) or a modified polypeptide having reverse transcriptase activity generates one or more nucleic acid (e.g., cDNA) molecule(s) complementary to a template at an error rate that is at least about 10000 times lower, at least about 1500 times lower, at least about 1000 times lower, at least about 500 times lower, at least about 100 times lower, at least about 95 times lower, at least about 90 times lower, at least about 85 times lower, at least about 80 times lower, at least about 75 times lower, at least about 70 times lower, at least about 65 times lower, at least about 60 times lower, at least about 55 times lower, at least about 50 times lower, at least about 45 times lower, at least about 40 times lower, at least about 35 times lower, at least about 30 times lower, at least about 25 times lower, at least about 20 times lower, at least about 15 times lower, at least about 10 times lower, at least about 9 times lower, at least about 8 times lower, at least about 7 times lower, at least about 6 times lower, at least about 5 times lower, at least about 4 times lower, at least about 3 times lower, at least about 2 times lower, or at least about 1 time lower than the unmodified or naturally occurring enzyme or unmodified polypeptide having reverse transcriptase activity.

[0058] In some embodiments, the sequencing error rate will be equal to or less than about 1 in 100,000 bases. In some embodiments, the error rate of nucleotide sequence determination is equal to or less than about 1 in 10 bases, 1 in 20 bases, 3 in 100 bases, 1 in 100 bases, 1 in 1000 bases, and 1 in 10,000 bases.

[0059] The terms "polynucleotides", "nucleic acid", "nucleotides" and "oligonucleotides" can be used interchangeably. They can refer to a polymeric form of nucleotides of any length, either deoxyribonucleotides or ribonucleotides, fragments, or analogs thereof. The following are examples of polynucleotides: coding or non-coding regions of a gene or gene fragment, loci (locus) defined from linkage analysis, exons, introns, messenger RNA (mRNA), transfer RNA, transfer-messenger RNA, ribosomal RNA, antisense RNA, small nuclear RNA (snRNA), small nucleolar RNA (snoRNA), micro-RNA (miRNA), small interfering RNA (siRNA), ribozymes, cDNA, recombinant polynucleotides, branched polynucleotides, plasmids, vectors, isolated DNA of any sequence, isolated RNA of any sequence, nucleic acid probes, and primers. A polynucleotide may comprise modified nucleotides, such as methylated nucleotides and nucleotide analogs. If present, modifications to the nucleotide structure may be imparted before or after assembly of the polymer. The sequence of nucleotides may be interrupted by non-nucleotide components. A polynucleotide may be further modified after polymerization, such as by conjugation with a labeling component. A nucleic acid described herein can contain phosphodiester bonds. In some embodiments, the nucleic acids can be DNA (including, e.g., genomic DNA, mitochondrial DNA, and cDNA), RNA (including, e.g., mRNA and rRNA) or a hybrid, where the nucleic acid contains any combination of deoxyribo- and ribo-nucleotides, and any combination of bases, including uracil, adenine, thymine, cytosine, guanine, inosine, xathanine hypoxathanine, isocytosine, and isoguanine. A polynucleotide is intended to encompass a singular nucleic acid as well as plural nucleic acids The polynucleotide may be composed of any polyribonucleotide or polydeoxyribonucleotide, which may be unmodified RNA or DNA or modified RNA or DNA. For example, polynucleotides may be composed of single- and double-stranded DNA, DNA that is a mixture of single- and double-stranded regions, single- and double-stranded RNA, and RNA that is mixture of single- and double-stranded regions, hybrid molecules comprising DNA and RNA that may be single-stranded or, more typically, double-stranded or a mixture of single- and double-stranded regions.

[0060] Ribosomal RNAs can make up as much as 80% or more of the total RNA in a sample. It is often desirable to separate mRNA from rRNA because rRNA can adversely affect the quantitative analysis of mRNA. One approach to separating rRNA from mRNA is to deplete the rRNA from the sample. One example, is the hybridization of rRNA molecules using oligonucleotides, for example, oligonucleotides homologous to the 17S rRNA, 18S rRNA, or 28S rRNA in the case of eukaryotic rRNAs, or to the 16S rRNA or 23S rRNA in the case of bacterial rRNA. The oligonucleotides are designed such that they can be "captured" and the hybridization product removed from the sample. For example, the oligonucleotides may be immobilized on a surface such as a column or a bead. MICROBExpress (Registered Trademark) and MICROBEnrich (Registered Trademark) (Ambion, Austin, Tex.) are examples of commercially available kits for the depletion of rRNA. Methods and compositions for the depletion or rRNA from a sample are described in US 2003 / 0175709A1. The poly(A) tail at the 3' end of most eukaryotic mRNAs can be used to separate these molecules away from rRNA and other non-mRNA species that lack this poly(A) tail. In some embodiments, the methods described herein comprises depleting ribosomal RNA, such as by hybridization of an oligonucleotide to an rRNA. In some embodiments, the method described herein comprises depleting rRNA and / or tRNA by oligonucleotide probe-guided endonucleolitic cleavage of at least one rRNA and / or tRNA sequence. In some embodiments, depletion can be partial or a complete depletion. In some embodiments, depletion comprises decreasing the number of rRNA and / or tRNA from a sample. In some embodiments, the method described herein relates to methods of depleting rRNA and / or transfer RNA (tRNA). In some embodiments, the methods described herein relate to depleting at least one transfer RNA (tRNA) from one or more template nucleic acid molecules. In some embodiments, depleting rRNA and / or tRNA occurs prior to annealing of a primer (e.g., one or more primers) to a template.

[0061] In one embodiment, the methods described herein relate to a method of depleting ribosomal and / or transfer RNA from a sample for library sequencing. In some embodiments, the method comprises providing a sample comprising RNA. In some embodiments, the RNA comprises ribosomal RNA (rRNA) and / or transfer RNA (tRNA). In some embodiments, the method comprises performing a polymerase chain reaction (PCR) to convert the rRNA and / or tRNA to double stranded DNA (dsDNA). In some embodiments, the method comprises partial or full (complete) amplification. In some embodiments, the method further comprises introducing a complex comprising a nuclease and / or a polynucleotide encoding a nuclease and at least one specifically designed guide oligonucleotide. In some embodiments, the at least one guide oligonucleotide comprises a sequence complementary to at least one rRNA and / or at least one tRNA. In some embodiments, the at least one guide oligonucleotide comprises at least one sequence complementary to at least one dsDNA. In some embodiments, the nuclease or polynucleotide encoding the nuclease cleaves at least one strand of the dsDNA. In some embodiments, the nuclease or polynucleotide encoding the nuclease cleaves the rRNA and / or the tRNA and / or the dsDNA, thereby depleting the rRNA and / or the tRNA from the sample. In some embodiments, the nuclease is Cas9 or the polynucleotide encodes Cas9 or a functional variant thereof. In some embodiments, the method comprises denaturing the dsDNA into single-stranded DNA (ssDNA) strands. In some embodiments, the methods described herein further comprise introducing at least one oligonucleotide (e.g., specifically designed oligonucleotide) comprising a binding molecule and at least one sequence complementary to at least one ssDNA strand to form a hybridized complex of the oligonucleotide and the at least one ssDNA strand. In some embodiments, the method comprises immobilizing the hybridized complex to at least one solid support. In some embodiments, immobilizing the hybridized complex causes the hybridized complex to be removed from a sample. In some embodiments, the solid support comprises streptavidin. In some embodiments, the methods described herein comprise introducing at least one oligonucleotide (e.g., specifically designed oligonucleotide) comprising a binding molecule and at least one sequence complementary to at least one rRNA and / or tRNA to form a complex comprising the oligonucleotide and the at least one rRNA and / or tRNA. In some embodiments, the method described herein further comprises immobilizing the complex to at least one solid support. In some embodiments, immobilizing the complex causes the complex to be removed from a sample. In some embodiments, the solid support comprises streptavidin. In some embodiments, the binding molecule is biotin.

[0062] In some embodiments, any of the methods described herein comprises a nuclease or polynucleotide encoding the nuclease. In some embodiments, the nuclease or polynucleotide encoding the nuclease cleaves at least one strand of a dsDNA. In some embodiments, cleavage of dsDNA is an intermediate product of library preparation. In some embodiments, cleavage of dsDNA includes rRNA and / or tRNA (coding sequences). In some embodiments, oligo-guided nucleolitic cleavage may not or does not require denaturing dsDNA. In some embodiments, not requiring dsDNA denaturation is a significant improvement of the methods described herein. In some embodiments, the nuclease or a polynucleotide encoding the nuclease is Cas9, or a polynucleotide encoding Cas9, or a functional variant thereof.

[0063] In one embodiment, the method described herein comprises adding a nuclease complex to a plurality of double-stranded nucleic acid molecules. In some embodiments, the nuclease complex comprises a Cas9 nuclease or a functional variant thereof and at least one synthetic guide oligonucleotide. In some embodiments, the synthetic guide oligonucleotide is complementary to a ribosomal ribonucleic acid (rRNA) and / or transfer ribonucleic acid (tRNA) region. In some embodiments, the region is in at least one double-stranded nucleic acid molecule. In some embodiments, the method comprises permitting the complex to cleave an rRNA and / or a tRNA region. In some embodiments the region is present in at least one double-stranded nucleic acid molecule. In some embodiments, the method provides at least one cleaved double-stranded nucleic acid molecule. In some embodiments, the method comprises subjecting the at least one cleaved double-stranded nucleic acid molecule or derivative thereof to sequencing (e.g., nucleic acid sequencing). In some embodiments, the method comprises sequencing a nucleic acid sequence of at least one double-stranded nucleic acid molecule lacking an rRNA and / or a tRNA region. In some embodiments, the method comprises sequencing a nucleic acid sequence of at least one double-stranded nucleic acid molecule comprising an rRNA and / or a tRNA region. In some embodiments, the method comprises sequencing a mixture of nucleic acid sequence wherein the mixture comprises at least one double-stranded nucleic acid molecule comprising an rRNA and / or a tRNA region and at least one double-stranded nucleic acid molecule lacking an rRNA and / or a tRNA region.

[0064] In one embodiment, the method of producing a cell free deoxyribonucleic acid (cfDNA) library as described herein comprises: providing a sample comprising cfDNA; denaturing the cfDNA to produce a single stranded DNA (ssDNA) sample; introducing, in the presence of nucleotides and / or a catalytic metal, a complex comprising a template, a primer, and a reverse transcriptase to the ssDNA sample, wherein the reverse transcriptase extends the primer on the template and subsequently template jumps to the ssDNA sample to produce a double stranded DNA (dsDNA) sample, and wherein the dsDNA comprises at least one nick between the template and the ssDNA; introducing a polymerase comprising a 3'-to-5' exonuclease activity to generate a dsDNA with blunt ends and / or a 3'-overhang; introducing an asymmetric adapter comprising a nucleic acid duplex with a single-stranded overhang at the 5' end, wherein the asymmetric adapter is ligated to the 5' end of the dsDNA, and wherein the single-stranded overhang comprises a sequence complementary to at least one polymerase chain reaction (pcr) amplification primer; and performing a pcr reaction to amplify only one strand of the dsDNA.

[0065] In one embodiment, the method of producing a cell free deoxyribonucleic acid (cfDNA) library described herein comprises providing a sample comprising cfDNA. In some embodiments, the method comprises denaturing the cfDNA to produce a single stranded DNA (ssDNA) sample. In some embodiments, the method comprises introducing a terminal deoxynucleotidyl transferase (TdT) and a deoxyadenosine triphosphate (dATP) to the ssDNA sample to generate a poly(A) and / or a poly(C) tail. In some embodiments, the method comprises introducing a non-extendable nucleotide. In some embodiments, the method comprises annealing a complex comprising a primer and a first adapter to the tail of the ssDNA sample. In some embodiments, the complex comprises a sequence complementary to the tail. In some embodiments, the method comprises introducing, in the presence of nucleotides and / or a catalytic metal, a reverse transcriptase (e.g., a modified reverse transcriptase) and a complex comprising an acceptor and a second adapter to produce a double strand DNA (dsDNA) sample. In some embodiments, the nucleotides comprise degradable nucleotides. In some embodiments, the reverse transcriptase extends the primer and subsequently template jumps to the complex to continue extension. In some embodiments, the complex comprises a nucleotide block to prevent the reverse transcriptase from reaching the end of the complex and jumping to another complex. In some embodiments, the dsDNA comprises an original strand and a copy strand. In some embodiments, the original strand comprises at least one nick between the complex and the ssDNA. In some embodiments, the copy strand comprises at least one degradable nucleotide. In some embodiments, the method further comprises introducing a polymerase comprising a 3'-to-5' exonuclease activity to generate a dsDNA with blunt ends or a 3'-overhang, and / or a DNA ligase to ligate the at least one nick. In some embodiments, the method further comprises introducing at least one uracil-DNA glycosylase to degrade at least one degradable nucleotide. In some embodiments, the method further comprises performing a polymerase chain reaction (PCR) comprising a primer (e.g., at least a first primer and / or at least a first and a second primer) to amplify the original strand. In some embodiments, the primer (e.g., the first primer) comprises a sequence complementary to the first adapter and the second primer comprises a sequence complementary to the second adapater.

[0066] In one embodiment, the method described herein is a method of producing a library for sequencing. In some embodiments, the method comprises providing a sample comprising cell free ribonucleic acid (cfRNA). In some embodiments, the method comprises subjecting the sample to high temperature. In some embodiments, the high temperature is sufficient to allow for transphosphorylation of the RNA (e.g., cfRNA). In some embodiments, the method further comprises introducing a phosphatase. In some embodiments, the phosphatase can convert a phosphate moiety of an RNA to a 3'-hydroxyl group. In some embodiments, the method further comprises introducing an adenosine triphosphate and a polymerase to generate a poly(A) tail on the 3'-hydroxyl group of the RNA. In some embodiments, the method further comprises introducing, in the presence of nucleotides, a primer, an acceptor, and a reverse transcriptase. In some embodiments, the primer comprises a sequence complementary to the poly(A) tail thereby annealing to the poly(A) tail. In some embodiments, the reverse transcriptase extends the primer and subsequently template jumps to the acceptor to continue extension. In some embodiments, the method further comprises introducing at least one solid support to immobilize excess primer and non-specific primer products to the at least one solid support, thereby removing the excess primer and the non-specific primer products from the sample. In some embodiments, the method further comprises performing a polymerase chain reaction (PCR) reaction to amplify the RNA. In some embodiments, the method further comprises using an isothermal amplification reaction.

[0067] In one embodiment, the method described herein is a method for preparing a nucleic acid library for sequencing. In some embodiments, the method comprises obtaining a plurality of nucleic acid molecules. In some embodiments, the method comprises inducing a non-enzymatic intramolecular transphosphorylation of at least one nucleic acid molecule (e.g., in the plurality of nucleic acid molecules). In some embodiments, the non-enzymatic intramolecular transphosphorylation can occur by increasing temperature (e.g., increase the temperature of a plurality of nucleic acid molecules). In some embodiments, non-enzymatic intramolecular transphosphorylation and / or an increase of temperature results in a nucleic acid molecule having a free 5'-phosphate moiety (e.g., a plurality of nucleic acid molecules can have a free 5'-phosphate moiety). In some embodiments, the method comprises adding a phosphatase to the nucleic acid molecules with the free 5'-phosphate moiety. In some embodiments, the phosphatase converts one or more of the free 5'-phosphate moieties to a hydroxyl group. In some embodiments, this results in a plurality of nucleic acid molecules to have a free hydroxyl group. In some embodiments, the method comprises mixing (e.g., in the presence of an amount of adenosine triphosphates) a plurality of nucleic acid molecules and a polymerase. In some embodiments, the polymerase generates a poly(A) tail on the free hydroxyl group. In some embodiments, the method comprises mixing, in the presence of nucleotides, (i) one or more primers comprising a sequence complementary to said poly(A) tail; (ii) one or more acceptor nucleic acid molecules; and (iii) a modified reverse transcriptase. In some embodiments, the modified reverse transcriptase generates a plurality of continuous complementary deoxyribonucleic acid molecule by reverse transcribing a sequence of an annealed template nucleic acid molecule, migrating to an acceptor nucleic acid molecule, and reverse transcribing a sequence of said acceptor nucleic acid molecule. In some embodiments, the method comprises adding at least one solid support. In some embodiments, the solid support immobilizes an excess of the one or more primers comprising a sequence complementary to said poly(A) tail. In some embodiments, the method comprises performing a polymerase chain reaction (PCR) reaction. In some embodiments, the method comprises performing an isothermal amplification.

[0068] In one embodiment, the method described herein is a method of producing a library for sequencing. In some embodiments, the method comprises providing a sample comprising at least one nucleic acid molecule (such as ribonucleic acid (e.g., cfRNA)). In some embodiments, the method comprises subjecting the sample (or the nucleic acid molecule) to high temperature sufficient to allow for transphosphorylation of the nucleic acid molecule (e.g., RNA). In some embodiments, the method further comprises adding a catalytic metal (e.g., magnesium) and / or a polyamine. In some embodiments, the method comprises introducing a phosphatase to convert a phosphate moiety of a nucleic acid molecule (e.g., RNA) to a 3'-hydroxyl group. In some embodiments, the method comprises introducing an adenosine triphosphate and a polymerase to generate a poly(A) tail. In some embodiments, the poly(A) tail is generated on the 3'-hydroxyl group of the nucleic acid molecule (e.g., RNA). In some embodiments, the method comprises introducing, in the presence of nucleotides, a primer, an acceptor, and a reverse transcriptase to the sample or to the nucleic acid molecule. In some embodiments, the primer comprises a sequence complementary to the poly(A) tail thereby annealing to the poly(A) tail. In some embodiments, the reverse transcriptase extends the primer and subsequently template jumps to the acceptor to continue extension. In some embodiments, the method comprises introducing at least one solid support. In some embodiments, the solid support immobilizes excess primer and non-specific primer products. In some embodiments, the excess primer and the non-specific primer products is removed from the sample / mixture. In some embodiments, the method further comprises performing a polymerase chain reaction (PCR) reaction to amplify the nucleic acid molecule (e.g., RNA). In some embodiments, the method further comprises an isothermal amplification reaction.

[0069] In one embodiment, the methods described herein is a method of depleting rRNA and / or tRNA and / or to a method comprising reverse transcribing at least one nucleic acid molecule by performing an amplification reaction. In some embodiments, at least one nucleic acid moleculte is rRNA and / or tRNA. In some embodiments, the amplification reaction provides a plurality of double-stranded nucleic acid molecules (e.g., cDNA). In some embodiments, the method comprises adding a nuclease or a polypeptide comprising a nuclease and / or a guide oligonucleotide. In some embodiments, the method comprises adding a complex comprising a nuclease or a polypeptide comprising a nuclease and a guide oligonucleotide. In some embodiments, the nuclease or polypeptide comprising the nuclease is Cas9 or a polypeptide comprising Cas9. In some embodiments, the guide oligonucleotide is complementary to region of a nucleic acid molecule. In some embodiments, the guide oligonucleotide is complementary to a pre-determined region in at least one nucleic acid molecule (e.g., double-stranded nucleic acid molecule). In some embodiments, the oligonucleotide directs the nuclease (e.g., Cas9) to the site of cleavage. In some embodiments, the complex comprising a nuclease and a guide oligonucleotide cleaves a region or a pre-determined region of the nucleic acid molecule. In some embodiments, the cleavage is at a gene. In some embodiments, the method comprises sequencing the cleaved nucleic acid molecules (e.g., cleaved double stranded nucleic acid molecules) (e.g., sequencing a library of cleaved nucleic acid molecules). In some embodiments the double-stranded nucleic acid molecules comprises sequences derived from an rRNA, a tRNA, or both an rRNA and a tRNA. In some embodiments, the pre-determined region of at least one double-stranded nucleic acid molecule is a region of an rRNA, a tRNA, or both (e.g., a combination). In some embodiments, the pre-determined region is a region of an rRNA. In some embodiments, the pre-determined region is a region of a tRNA. In some embodiments the method does not require denaturation of nucleic acid molecules. In some embodiments, the method does not require denaturation of the plurality of double-stranded nucleic acid molecules. In some embodiments, a double-stranded nucleic acid molecule comprises a sequence derived from an rRNAs and / or a tRNA prior to sequencing. In some embodiments, the double-stranded nucleic acid molecules comprise a cDNA.

[0070] In one embodiment, the methods described herein is a method for preparing a concatemer of nucleic acid molecules. In some embodiments, the method comprises processing ends of a plurality of double-stranded nucleic acid molecules. In some embodiments, the method comprises adding a first plurality of adaptor molecules to the plurality of double stranded nucleic acid molecules. In some embodiments, the first plurality of adaptor molecules comprise one or more overhang sequences. In some embodiments, at least two of the one or more overhang sequences are complentary to each other. In some embodiments, the method provides a first plurality of adaptor connected double-stranded nucleic acid molecules. In some embodiments, the method comprises adding a polymerizing enzyme (e.g., adding a polymerase enzyme to the first plurality of adaptor connected double-stranded nucleic acid molecules). In some embodiments, adding a polymerase enzyme is in the absence of a primer. In some embodiments, the method does not comprise adding a primer. In some embodiments, the polymerizing enzyme forms a first set of adaptor connected double-stranded nucleic acid concatemers. In some embodiments, forming a first set of adaptor connected double-stranded nucleic acid concatemers is by joining two or more adaptor connected double-stranded nucleic acid molecules by the one or more overhang sequences. In some embodiments, the method comprises adding a second plurality of adaptor molecules to the first set (e.g., first adaptor molecules). In some embodiments, the second plurality of adaptor molecules comprise one or more overhang sequences. In some embodiments, at least two of the one or more overhang sequences are complementary to each other. In some embodiments, the method provides a second set of adaptor connected double-stranded nucleic acid molecules. In some embodiments, any one of the previous embodiments can be repeated with a set of adaptor molecules to yield a concatemer comprising a predetermined average length.

[0071] In one embodiment, the methods described herein is a method for preparing a concatemer of nucleic acid molecules. In some embodiments, the method comprises subjecting at least one nucleic acid molecule and / or a plurality of double-stranded nucleic acid molecules to end-repair. In some embodiments, the method comprises adding at least one or a plurality of adaptor molecules to the at least one nucleic acid molecule and / or the plurality of double-stranded nucleic acid molecules. In some embodiments, adding at least one or a (first) plurality of adaptor molecules to the at least one nucleic acid molecule and / or the plurality of double stranded nucleic acid molecules comprises ligation. In some embodiments, adding at least one or a (first) plurality of adaptor molecules to the at least one nucleic acid molecule and / or the plurality of double stranded nucleic acid molecules comprises a reverse transcriptase (e.g., R2 reverse transcriptase, or a modified reverse transcriptase). In some embodiments, In some embodiments, the at least one or a plurality of adaptor molecules comprise one or more overhang sequences. In some embodiments, at least two overhang sequences are complentary to each other (e.g., thereby providing a (first) plurality of adaptor connected double-stranded nucleic acid molecules). In some embodiments, the at least one or a plurality of adaptor molecules comprise a sequence (e.g., overhang sequence) that attaches / ligates to the 3' end of the nucleic acid molecule and / or a sequence (e.g., overhang sequence) that attaches / ligates to the 5' end of the nucleic acid molecule. In some embodiments, the nucleic acid molecule comprises adaptors on both the 3' and the 5' end. In some embodiments, the adaptor that binds to the 3' end is complementary to the adaptor that binds to the 5' end. In some embodiments, the sequence of the adaptors is unknown. In some embodiments, the sequence of the adaptors is pre-determined. In some embodiments, the adaptor serves as a template and / or as a primer. In some embodiments, the adaptor that binds to the 3' end of one nucleic acid molecule can bind to an adaptor on the 5' end of another nucleic acid molecule. In some embodiments, the method further comprises adding a polymerase enzyme to the adaptor connected to a nucleic acid molecule. In some embodiments, the method further comprises adding a polymerase to the (first) plurality of adaptor connected double-stranded nucleic acid molecules. In some embodiments, the polymerase is added in the absence of a primer. In some embodiments, the polymerase enzyme forms a first set of adaptor connected double-stranded nucleic acid concatemers by joining two or more adaptor connected double-stranded nucleic acid molecules by the one or more overhang sequences. In some embodiments, the polymerase permits that the adaptor connected to the nucleic acid molecule form concatemers. In some embodiments, the method comprises adding a second plurality of adaptor molecules to the first set. In some embodiments, the second plurality of adaptor molecules comprise one or more overhang sequences. In some embodiments, the at least two overhang sequences are complementary to each other. In some embodiments, a second set of adaptor connected double-stranded nucleic acid molecules is formed. In some embodiments, the concatemer length or the number of attached templates can be determined, for example, by tagging the adaptors with modified nucleotides (e.g., by introducing methylated nucleotides or by inserting dUTP). In some embodiments the length of the concatemer can be regulated based on the ratio between modified / unmodified adaptors. In some embodiments the adaptor sequences can serve as a homology priming location (annealed to the homology spot ssDNA fragments serve as template and primer). In some embodiments, the method comprises amplifying the concatemers by PCR or isothermal reaction. In some embodiments, the reaction in the PCR undergoes a selected number of cycles (the more cycles, the longer the concatemer) or time (isothermal amplification). In some embodiments, the reaction is stopped and the (long) dsDNA concatemers are ligated with two unique dsDNA adaptors. In some embodiments, the length of the concatemer can be manipulated. In some embodiments, the length of the concatemer can be determined at least based on the number of PCR cycles, and / or the amount of time (e.g., in an isothermal amplification), and / or based on the modified nucleotide present in the adaptor. In some embodiments, the adaptor comprises a unique molecular identifier sequence (UMI). In some embodiments, the polymerase enzyme joins two or more adaptor connected double-stranded nucleic acid molecules in a PCR or isothermal amplification reaction. In some embodiments, the adaptor comprises at least one modified nucleotide.

[0072] In some embodiments, nucleic acid from a biological sample obtained from a subject is amplified. In some cases, the biological sample is obtained directly from the subject. In some embodiments, a biological sample obtained directly from a subject refers to a biological sample that has been further processed after being obtained from the subject. In some embodiments, a biological sample obtained directly from a subject refers to a biological sample that has not been further processed after being obtained from the subject, with the exception of any approach used to collect the biological sample from the subject for further processing. For example, blood is obtained directly from a subject by accessing the subject's circulatory system, removing the blood from the subject (e.g., via a needle), and entering the removed blood into a receptacle. The receptacle may comprise reagents (e.g., anticoagulants) such that the blood sample is useful for further analysis. In another example, a swab may be used to access epithelial cells on an oropharyngeal surface of the subject. After obtaining the biological sample from the subject, the swab containing the biological sample can be contacted with a fluid (e.g., a buffer) to collect the biological fluid from the swab.

[0073] In some embodiments, a biological sample has been purified. In some embodiments, a biological sample has not been purified. In some embodiments, the nucleic acid of a biological sample has not been extracted when the biological sample is provided to a tube. For example, the RNA or DNA in a biological sample may not be extracted from the biological sample when providing the biological sample to a tube. In some embodiments, a target nucleic acid (e.g., a target RNA or target DNA) present in a biological sample may not be concentrated prior to providing the biological sample to a reaction vessel (e.g., a tube). Any suitable biological sample that comprises nucleic acid may be obtained from a subject.

[0074] Describrd herein are non-naturally occurring or modified enzymes (e.g., a non-naturally occurring or modified reverse transcriptase, modified reverse transcriptase) or a modified polypeptide having reverse transcriptase activity that has an improved enzyme property compared to a naturally occurring or wild type or unmodified enzyme (e.g., a wild type reverse transcriptase) or unmodified polypeptide having reverse transcriptase activity. In some embodiments, the non-naturally occurring or modified enzyme is an enzyme with reverse transcriptase activity. In some embodiments, the non-naturally occurring or modified enzyme is a modified reverse transcriptase. In some embodiments, the non naturally occurring or modified enzyme is a modified non-retroviral reverse transcriptase. In some embodiments, the non-naturally occurring or modified enzyme is a modified non-LTR retrotransposon. In some embodiments, the non-naturally occurring or modified enzyme is a modified R2 reverse transcriptase. In some embodiments, a non-naturally occurring or modified enzyme or a modified polypeptide having reverse transcriptase activity can amplify a template nucleic acid molecule at a processivity of at least about 80% per base, of at least about 85% per base, of at least about 88% per base, of at least about 89% per base, of at least about 90% per base, of at least about 91% per base, of at least about 92% per base, of at least about 93% per base, of at least about 94% per base, of at least about 95% per base, of at least about 96% per base, of at least about 97% per base, of at least about 98% per base, of at least about 99% per base, of at least about 99.5% per base, or of about 100% per base.

[0075] In some embodiments, a non-naturally occurring or modified enzyme or a modified polypeptide having reverse transcriptase activity can amplify or is capable of amplifying a template nucleic acid molecule at a processivity measured at a temperature of between about 12 °C and about 40 °C. In some embodiments, the temperature is between about 10 °C and about 35 °C, between about 12 °C and about 30 °C, between about 25 °C and about 40 °C, or between about 12 °C and about 42 °C. In some embodiments, the temperature is between about 8 °C to about 50 °C, between about 2 °C to about 60 °C, between about 8 °C to about 42 °C, between about 6 °C to about 32 °C, or between about 7 °C to about 35 °C.

[0076] In some embodiments, a non-naturally occurring or modified enzyme or a modified polypeptide having reverse transcriptase activity can amplify or is capable of amplifying a template nucleic acid molecule at a processivity of at least about 80% per base at a temperature at about or at most about 4 °C, at about or at most about 8 °C, at about or at most about 12 °C, at about or at most about 15 °C, at about or at most about 20 °C, at about or at most about 25 °C, at about or at most about 30 °C, at about or at most about 35 °C, at about or at most about 40 °C, or at about or at most about 42 °C; of at least about 85% per base at a temperature of about or at most about 12 °C, at about or at most about 15 °C, at about or at most about 20 °C, at about or at most about 25 °C, at about or at most about 30 °C, at about or at most about 35 °C, at about or at most about 40 °C, at about or at most about 42 °C, at about or at most about 45 °C, at about or at most about 50 °C; of at least about 89% per base at a temperature at about or at most about 4 °C, at about or at most about 8 °C, at about or at most about 12 °C, at about or at most about 15 °C, at about or at most about 20 °C, at about or at most about 25 °C, at about or at most about 30 °C, at about or at most about 35 °C, at about or at most about 40 °C, or at about or at most about 42 °C; of at least about 90% per base at a temperature of about or at most about 12 °C, at about or at most about 15 °C, at about or at most about 20 °C, at about or at most about 25 °C, at about or at most about 30 °C, at about or at most about 35 °C, at about or at most about 40 °C, at about or at most about 42 °C, at about or at most about 45 °C, at about or at most about 50 °C; of at least about 91% per base at a temperature at about or at most about 4 °C, at about or at most about 8 °C, at about or at most about 12 °C, at about or at most about 15 °C, at about or at most about 20 °C, at about or at most about 25 °C, at about or at most about 30 °C, at about or at most about 35 °C, at about or at most about 40 °C, or at about or at most about 42 °C; of at least about 85% per base at a temperature of about or at most about 12 °C, at about or at most about 15 °C, at about or at most about 20 °C, at about or at most about 25 °C, at about or at most about 30 °C, at about or at most about 35 °C, at about or at most about 40 °C, at about or at most about 42 °C, at about or at most about 45 °C, at about or at most about 50 °C; of at least about 95% per base at a temperature at about or at most about 4 °C, at about or at most about 8 °C, at about or at most about 12 °C, at about or at most about 15 °C, at about or at most about 20 °C, at about or at most about 25 °C, at about or at most about 30 °C, at about or at most about 35 °C, at about or at most about 40 °C, or at about or at most about 42 °C; of at least about 85% per base at a temperature of about or at most about 12 °C, at about or at most about 15 °C, at about or at most about 20 °C, at about or at most about 25 °C, at about or at most about 30 °C, at about or at most about 35 °C, at about or at most about 40 °C, at about or at most about 42 °C, at about or at most about 45 °C, at about or at most about 50 °C; of at least about 99% per base at a temperature at about or at most about 4 °C, at about or at most about 8 °C, at about or at most about 12 °C, at about or at most about 15 °C, at about or at most about 20 °C, at about or at most about 25 °C, at about or at most about 30 °C, at about or at most about 35 °C, at about or at most about 40 °C, or at about or at most about 42 °C; of at least about 85% per base at a temperature of about or at most about 12 °C, at about or at most about 15 °C, at about or at most about 20 °C, at about or at most about 25 °C, at about or at most about 30 °C, at about or at most about 35 °C, at about or at most about 40 °C, at about or at most about 42 °C, at about or at most about 45 °C, at about or at most about 50 °C; of at least about 99.5% per base at at a temperature at about or at most about 4 °C, at about or at most about 8 °C, at about or at most about 12 °C, at about or at most about 15 °C, at about or at most about 20 °C, at about or at most about 25 °C, at about or at most about 30 °C, at about or at most about 35 °C, at about or at most about 40 °C, or at about or at most about 42 °C; of at least about 85% per base at a temperature of about or at most about 12 °C, at about or at most about 15 °C, at about or at most about 20 °C, at about or at most about 25 °C, at about or at most about 30 °C, at about or at most about 35 °C, at about or at most about 40 °C, at about or at most about 42 °C, at about or at most about 45 °C, at about or at most about 50 °C; or of about 100% per base at a temperature at about or at most about 4 °C, at about or at most about 8 °C, at about or at most about 12 °C, at about or at most about 15 °C, at about or at most about 20 °C, at about or at most about 25 °C, at about or at most about 30 °C, at about or at most about 35 °C, at about or at most about 40 °C, or at about or at most about 42 °C; of at least about 85% per base at a temperature of about or at most about 12 °C, at about or at most about 15 °C, at about or at most about 20 °C, at about or at most about 25 °C, at about or at most about 30 °C, at about or at most about 35 °C, at about or at most about 40 °C, at about or at most about 42 °C, at about or at most about 45 °C, at about or at most about 50 °C.

[0077] In some embodiments, the non-naturally occurring or modified enzyme or a modified polypeptide having reverse transcriptase activity can amplify or is capable of amplifying a template nucleic acid molecule at a processivity of at least about 80% per base at a temperature of at most about 35 °C, of at least about 85% per base at a temperature of at most about 40 °C, of at least about 88% per base at a temperature of at most about 35 °C, of at least about 89% per base at a temperature of at most about 40 °C, of at least about 90% per base at a temperature of at most about 35 °C, of at least about 91% per base at a temperature of at most about 35 °C, of at least about 92% per base at a temperature of at most about 40 °C, of at least about 93% per base at a temperature of at most about 35 °C, of at least about 94% per base at a temperature of at most about 40 °C, of at least about 95% per base at a temperature of at most about 35 °C, of at least about 96% per base at a temperature of at most about 40 °C, of at least about 97% per base at a temperature of at most about 35 °C, of at least about 98% per base at a temperature of at most about 40 °C, of at least about 99% per base at a temperature of at most about 40 °C, of at least about 99.5% per base at a temperature of at most about 40 °C, or of about 100% per base at a temperature of at most about 40 °C.

[0078] In some embodiments, the improved enzyme property is selected from at least one of the following: improved stability (e.g., improved thermostability), improved specific activity, improved protein expression, improved purification, improved processivity, improved strand displacement, improved template jumping, improved DNA / RNA affinity, and improved fidelity. In some embodiments, a non-naturally occurring enzyme or a modified enzyme or a modified polypeptide having reverse transcriptase activity amplifies a template nucleic acid molecule. In some embodiments, the non-naturally occurring enzyme or the modified enzyme or the modified polypeptide having reverse transcriptase activity that amplifies a template nucleic acid molecule has a performance index greater than about 1, greater than about 2, greater than about 3, greater than about 4, greater than about 5, greater than about 6, greater than about 7, greater than about 8, greater than about 9, greater than about 10, greater than about 15, greater than about 20, greater than about 25, greater than about 30, greater than about 35, greater than about 40, greater than about 45, greater than about 50, greater than about 60, greater than about 70, greater than about 80, greater than about 90, or greater than about 100 for at least one enzyme property. In some embodiments, the enzyme property and / or the performance index is performed at a temperature equal to or lower than or at most about 50 °C, equal to or lower than or at most about 42 °C, equal to or lower than or at most about 40 °C, equal to or lower than or at most about 39 °C, equal to or lower than or at most about 38 °C, equal to or lower than or at most about 37 °C, equal to or lower than or at most about 36 °C, equal to or lower than or at most about 35 °C, equal to or lower than or at most about 34 °C, equal to or lower than or at most about 33 °C, equal to or lower than or at most about 32 °C, equal to or lower than or at most about 31 °C, equal to or lower than or at most about 30 °C, equal to or lower than or at most about 29 °C, equal to or lower than or at most about 28 °C, equal to or lower than or at most about 27 °C, equal to or lower than or at most about 26 °C, equal to or lower than or at most about 25 °C, equal to or lower than or at most about 23 °C, equal to or lower than or at most about 20 °C, equal to or lower than or at most about 15 °C, equal to or lower than or at most about 13 °C, equal to or lower than or at most about 12 °C, equal to or lower than or at most about 10 °C, equal to or lower than or at most about 8 °C, equal to or lower than or at most about 4 °C. In some embodiments, the non-naturally occurring enzyme or the modified enzyme (e.g., modified reverse transcriptase) or the modified polypeptide having reverse transcriptase activity exhibits a processivity for a given nucleotide substrate that is at least about 5%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 37.5%, at least about 40%, at least about 45%, at least about 50%, at least about 60%, at least about 70%, at least about 75%, at least about 80%, at least about 90%, at least about 95%, at least about 100%, at least about 110%, at least about 125%, at least about 150%, at least about 170%, at least about 190%, at least about 200%, at least about 250%, at least about 500%, at least about 750%, at least about 1000%, at least about 5000%, or at least about 10000% higher than the processivity of a reference enzyme or a reference polypeptide for the same nucleotide substrate. In some embodiments, the non-naturally occurring enzyme is a non-naturally occurring reverse transcriptase enzyme. In some embodiments, the modified enzyme is a modified reverse transcriptase.

[0079] Described herein are processes and / or methods that require considerably less hands-on time, the protocol is much simpler to perform and requires a much shorter duration time than other methods used for RNA sequencing and / or liquid biopsy, for example. In some embodiments, the methods and processes described herein comprise a protocol that is less than about 2 h and / or less than about 30 min of hands-on time. In some embodiments, the protocol is less than about 20 h, less than about 15 h, less than about 12 h, less than about 11 h, less than about 10 h, less than about 9 h, less than about 8 h, less than about 7 h, less than about 6 h, less than about 5 h, less than about 4 h, less than about 3 h, less than about 2.5 h, less than about 2 h, less than about 1.5 h, less than about 1 hour, or less than about 30 min. In some embodiments, the hands-on time is less than about 5 h, less than about 4 h, less than about 3 h, less than about 2.5 h, less than about 2 h, less than about 1.5 h, less than about 1 hour, less than about 50 min, less than about 40 min, less than about 35 min, less than about 30 min, less than about 25 min, less than about 20 min, or less than about 15 min.

[0080] In some embodiments, the method for preparing a nucleic acid library and / or a complementary cDNA library described herein comprises preparing the library in at most about 1 hour, at most about 2 h, at most about 3 h, at most about 4 h, at most about 5 h, at most about 7 h, at most about 10 h, at most about 15 h, or at most about 20 h.

[0081] In one embodiment, described herein are methods and processes that enable the discovery of novel markers and mutations for cancer, and / or approaches for precision medicine. In some embodiments, the methods and processes described herein provide for higher sensitivity to capture minor allele in ctDNA of <0.1% (available current methods have sensitivity >1%). In some embodiments, the methods and / or processes described herein comprise a 1-pot (e.g., single vessel), 1-step protocol, and the library is prepared from a sample in an amount of time that is equal to or less than about 2 h. See figure 2.

[0082] The methods described herein relate to methods for preparing a modified reverse transcriptase, which method comprises at least one of the following steps: (a) subjecting a nucleic acid sequence encoding a reverse transcriptase enzyme to random or rational mutagenesis; (b) subjecting a nucleic acid sequence encoding a reverse transcriptase enzyme to truncation of amino acids; (c) subjecting a nucleic acid sequence encoding a reverse transcriptase enzyme to alteration comprising an insertion, a deletion or a substitution of an amino acid residue; and (d) subjecting a nucleic acid sequence encoding a reverse transcriptase enzyme to fusion with a protein or domain. In some embodiments, the nucleic acid sequence obtained in any one of steps (a) to (d) is expressed in a host cell. In some embodiments, the modified reverse transcriptase comprises at least one improved enzyme property relative to a wild type or unmodified reverse transcriptase. In some embodiments the nucleic acid sequence is DNA, RNA, or a combination of RNA and DNA. In some embodiments, the method comprises screening for host cells expressing modified reverse transcriptase(s). In some embodiments, the method comprises preparing modified reverse transcriptase(s) expressed by the host cell(s). In some embodiments, the method may comprise purifying the modified reverse transcriptase(s) according to any method including any method described herein. In some embodiments, the method may comprise determining the reverse transcriptase activity, estimating the reverse transcriptase activity fractions, and / or testing the stability and / or robustness of the modified reverse transcriptase(s). In some embodiments, determining the reverse transcriptase activity, estimating the reverse transcriptase activity fractions, and / or testing the stability and / or robustness of the modified reverse transcriptase(s) are performed or tested using a reverse transcriptase activity assay. In some embodiments, the reverse transcriptase activity, the reverse transcriptase active fraction, and / or the stability and / or robustness of the modified reverse transcriptase(s) is increased / improved compared to the unmodified or naturally occurring reverse transcriptase.

[0083] The methods described herein relate to methods for preparing a complementary deoxyribonucleic acid (cDNA) molecule. In some embodiments, the method comprises annealing a primer to a template nucleic acid molecule, thereby generating an annealed template nucleic acid molecule. In some embodiments, the method further comprises mixing, in the presence of nucleotides, the annealed template nucleic acid molecule, a one or more acceptor nucleic acid molecules, and a modified reverse transcriptase. In some embodiments, the modified reverse transcriptase generates a plurality of continuous complementary deoxyribonucleic acid molecules. In some embodiments, the plurality of continuous complementary deoxyribonucleic acid molecules are prepared in at most about 2 h. In some embodiments, the plurality of continuous complementary deoxyribonucleic acid molecules is generated by having the modified reverse transcriptase reverse transcribe a sequence of the annealed template nucleic acid molecule. In some embodiments, the modified reverse transcriptase then migrates to an acceptor nucleic acid molecule (e.g., one or more acceptor nucleic acid molecules). In some embodiments, the reverse transcriptase (e.g., modified reverse transcriptase) is able to reverse transcribe a sequence of the template and / or the acceptor nucleic acid molecule at a temperature of from about 12 °C to about 42 °C. In some embodiments, the reverse transcriptase (e.g., modified reverse transcriptase) is able to reverse transcribe a sequence of the template and / or the acceptor nucleic acid molecule at a temperature of from about 8 °C to about 50 °C (e.g., about 8 °C, about 15 °C, about 20 °C, about 25 °C, about 30 °C, about 35 °C, about 40 °C, about 45 °C, about 48 °C). In some embodiments, the reverse transcriptase (e.g., modified reverse transcriptase) is able to reverse transcribe a sequence of the template and / or the acceptor nucleic acid molecule at a temperature of at most about 4 °C, at most about 8 °C, at most about 15 °C, at most about 20 °C, at most about 25 °C, at most about 30 °C, at most about 35 °C, at most about 40 °C, at most about 45 °C, or at most about 48 °C. In some embodiments, reverse transcription occurs at an error rate of at most about 5%. In some embodiments, the reverse transcriptase (e.g., modified reverse transcriptase) is capable of reverse transcribing the template and / or the acceptor nucleic acid molecule at an error rate of at most about 45%, at most about 40%, at most about 35%, at most about 30%, at most about 25%, at most about 20%, at most about 15%, at most about 10%, at most about 8%, at most about 7%, at most about 6%, at most about 5%, at most about 4%, at most about 3%, at most about 2%, or at most about 1%. In some embodiments, the reverse transcriptase (e.g., modified reverse transcriptase) can migrate from the template to the acceptor nucleic acid molecule independently of sequence identity between the template and the acceptor nucleic acid molecule. In some embodiments, the method is prepared in a single vessel. In some embodiments, the template nucleic acid molecule is a fragmented DNA template, a fragmented RNA template, a non-fragmented DNA template, a non-fragmented RNA template, or a combination thereof. In some embodiments, the method further comprises adding a tag to a template nucleic acid molecule, thereby generating a plurality of tagged continuous complementary deoxyribonucleic acid molecules. In some embodiments, the method further comprises performing a polymerase chain reaction amplification reaction, thereby forming one or more amplicons.

[0084] The methods described herein relate to methods for preparing a complementary deoxyribonucleic acid (cDNA) molecule using a modified reverse transcriptase. In some embodiments, the method for preparing a cDNA molecule is via template jumping. In some embodiments, the modified reverse transcriptase has an improved enzyme property compared to a naturally occurring or unmodified or wild type enzyme (e.g., wild type reverse transcriptase). In some embodiments, the method for preparing a cDNA molecule comprises: (a) annealing a primer to a template; and (b) mixing, in the presence of nucleotides (e.g., dNTPs), the template annealed to the primer with a modified reverse transcriptase and an acceptor nucleic acid molecule (e.g., acceptor RNA, DNA, or a combination thereof) under conditions sufficient to generate a cDNA molecule complementary to the template and / or to the acceptor nucleic acid molecule (Figure 3). In some embodiments, the enzyme (e.g., modified reverse transcriptase) generates a continuous cDNA molecule by migrating from the template to the acceptor nucleic acid molecule. In some embodiments, template jumping is independent of sequence identity between the template and the acceptor nucleic acid molecule. In some embodiments, step (a) and step (b) are done at the same time. In some embodiments, step (a) comprises step (b) (e.g., step (a) and step (b) are merged into one step). In some embodiments, at least one of step (a) and / or step (b) further comprises addition of a hot start thermostable polymerase. In some embodiments, the method described herein is performed in a single tube. In some embodiments, the method described herein further comprises a polymerase chain reaction (PCR) amplification reaction. In some embodiments, the PCR amplification reaction is performed in a single tube (e.g., the same one tube from steps (a) and (b)). In some embodiments, all the steps of the methods described herein are performed in a single tube.

[0085] Described herein is a method for preparing a concatemer of nucleic acid molecules for sequencing. In some embodiments, the method comprises ligating a nucleic acid molecule with a first adaptor. In some embodiments, the method further comprises amplifying the ligated nucleic acid molecule by performing a nucleic acid amplification reaction to form a concatemer. In some embodiments, the amplification reaction is performed in the absence of a primer. In some embodiments, the method further comprises ligating the concatemer with a second adaptor. In some embodiments, the adaptor(s) (first and / or second adaptor) is / are designed to allow recombination or homology based annealing and extension of molecules (e.g., nucleic acid molecules, and / or a template, and / or a primer, and / or an acceptor). In some embodiments, the nucleic acid amplification reaction is polymerase chain reaction (PCR) or isothermal amplification. In some embodiments, the first adaptor comprises a unique molecular identifier (UMI) sequence. In some embodiments, the first adaptor serves as a primer. In some embodiments, the first adaptor comprises single stranded nucleic acid. In some embodiments, the single stranded nucleic acid comprises single stranded DNA (ssDNA). In some embodiments, the second adaptor comprises double stranded nucleic acid. In some embodiments, the double stranded nucleic acid comprises double stranded DNA (dsDNA). In some embodiments, the first adaptor is different from the second adaptor. In some embodiments, the first adaptor comprises two or more adaptors. In some embodiments, the second adaptor comprises two or more adaptors. In some embodiments, both ends of the nucleic acid molecule comprise an adaptor. In some embodiments, only one end of the nucleic acid molecule comprises an adaptor. In some embodiments, both the 3' and the 5' ends of a nucleic acid molecule comprise an adaptor.

[0086] Described herein are methods for preparing a complementary deoxyribonucleic acid (cDNA) molecule using a modified reverse transcriptase. In some embodiments, the method for preparing a cDNA molecule is via template jumping. In some embodiments, the modified reverse transcriptase has an improved enzyme property compared to a naturally occurring or unmodified or wild type enzyme (e.g., wild type reverse transcriptase). In some embodiments, the method for preparing a cDNA molecule comprises mixing, in the presence of nucleotides (e.g., dNTPs), a primer, a template, a modified reverse transcriptase and an acceptor nucleic acid molecule (e.g., acceptor RNA, DNA, or a combination thereof) under conditions sufficient to generate a cDNA molecule complementary to the template and / or to the acceptor nucleic acid molecule. In some embodiments, the method comprises addition of a hot start thermostable polymerase (e.g., to the mixing step). In some embodiments, the method described herein is performed in a single tube. In some embodiments, the method described herein further comprises a polymerase chain reaction (PCR) amplification reaction. In some embodiments, the PCR amplification reaction is performed in a single tube (e.g., the same one tube as the mixing step). In some embodiments, all the steps of the method described herein is performed in a single tube (single vessel).

[0087] In some embodiments, the method for preparing a cDNA molecule comprises: (a) annealing one or more primer(s) to a template; and (b) mixing, in the presence of nucleotides (e.g., dNTPs), the template annealed to one or more primer(s) with a modified reverse transcriptase and an acceptor nucleic acid molecule (e.g., acceptor RNA, DNA, or a combination thereof) under conditions sufficient to generate a cDNA molecule complementary to the template and / or to the acceptor nucleic acid molecule (Figure 4). In some embodiments, the method for preparing a cDNA molecule is via template jumping. In some embodiments, step (a) and step (b) are done at the same time. In some embodiments, step (a) comprises step (b) (e.g., step (a) and step (b) are merged into one step). In some embodiments, at least one of step (a) and / or step (b) further comprises addition of a hot start thermostable polymerase. In some embodiments, the method described herein is performed in a single tube. In some embodiments, the method described herein further comprises a polymerase chain reaction (PCR) amplification reaction. In some embodiments, the PCR amplification reaction is performed in a single tube (e.g., the same one tube used in or from steps (a) and (b)). In some embodiments, all the steps of the method described herein is performed in a single tube.

[0088] In some embodiments, the method for preparing a cDNA molecule comprises mixing, in the presence of nucleotides (e.g., dNTPs), one or more primer(s), a template, a modified reverse transcriptase, and an acceptor nucleic acid molecule (e.g., acceptor RNA, DNA, or a combination thereof) under conditions sufficient to generate a cDNA molecule complementary to the template and / or to the acceptor nucleic acid molecule. In some embodiments, the method for preparing a cDNA molecule is via template jumping. In some embodiments, the method comprises addition of a hot start thermostable polymerase (e.g., to the mixing step). In some embodiments, the method described herein is performed in a single tube. In some embodiments, the method described herein further comprises a polymerase chain reaction (PCR) amplification reaction. In some embodiments, the PCR amplification reaction is performed in a single tube (e.g., the same one tube as the mixing step). In some embodiments, all the steps of the method described herein is performed in a single tube.

[0089] Described herein are methods for preparing a nucleic acid molecule comprising: mixing, in the presence of nucleotides (e.g., dNTPs), a fragment or degraded template (e.g., a nucleic acid fragment), a primer, a modified reverse transcriptase, and an acceptor nucleic acid molecule under conditions sufficient to generate a nucleic acid molecule (Figure 5A and 5B). In some embodiments, the acceptor nucleic acid molecule comprises a modified nucleotide. In some embodiments, the primer extension stops at the modified nucleotide. In some embodiments, the modified reverse transcriptase comprises at least one improved enzyme property relative to a wild type, naturally occurring, or unmodified reverse transcriptase. In some embodiments, the primer is an RNA primer. In some embodiments, the primer is an engineered primer (e.g., engineered RNA primer). In some embodiments, the primer has been optimized. In some embodiments, the primer is an optimized and / or engineered primer (e.g., optimized and / or engineered RNA primer). In some embodiments, the primer is RNA R2 primer. In some embodiments, the method for preparing a nucleic acid molecule is via template jumping. In some embodiments, the mixing step of the method described herein further comprises addition of a hot start thermostable polymerase. In some embodiments, the method described herein is performed in a single tube. In some embodiments, the method described herein further comprises a polymerase chain reaction (PCR) amplification reaction. In some embodiments, the PCR amplification reaction is performed in the same single tube. In some embodiments, all the steps of the method described herein is performed in a single tube.

[0090] Described herein are methods for preparing a nucleic acid molecule comprising: mixing, in the presence of nucleotides (e.g., dNTPs), a fragment or degraded template (e.g., a nucleic acid fragment), a donor complex, a modified reverse transcriptase, and an acceptor nucleic acid molecule under conditions sufficient to generate a nucleic acid molecule (Figure 6A and 6B). In some embodiments, the acceptor nucleic acid molecule comprises a modified nucleotide. In some embodiments, the primer extension stops at the modified nucleotide. In some embodiments, the modified reverse transcriptase comprises at least one improved enzyme property relative to a wild type or naturally occurring or unmodified reverse transcriptase. In some embodiments, the donor complex comprises a template and a primer. In some embodiments, the donor complex is a donor R2 complex. In some embodiments, the donor R2 complex comprises an RNA R2 primer. In some embodiments, the method for preparing a nucleic acid molecule is via template jumping. In some embodiments, the mixing step of the method described herein further comprises addition of a hot start thermostable polymerase. In some embodiments, the method described herein is performed in a single tube. In some embodiments, the method described herein further comprises a polymerase chain reaction (PCR) amplification reaction. In some embodiments, the PCR amplification reaction is performed in the same single tube (e.g., the same single tube used to prepare a nucleic acid molecule). In some embodiments, all the steps of the method described herein are performed in a single tube.

[0091] Described herein are methods for preparing a complementary deoxyribonucleic acid (cDNA) library using a modified reverse transcriptase. In some embodiments, the method for preparing a cDNA library uses template jumping. In some embodiments, the modified reverse transcriptase has an improved enzyme property compared to a naturally occurring or wild type or unmodified enzyme (e.g., wild type reverse transcriptase). In some embodiments, the method for preparing a cDNA library comprises: (a) annealing a primer or one or more primer(s) to a template; and (b) mixing, in the presence of nucleotides (e.g., dNTPs), the template annealed to the primer or the template annealed to one or more primer(s) with a modified reverse transcriptase and an acceptor nucleic acid molecule (e.g., acceptor RNA, DNA, or a combination thereof) under conditions sufficient to generate a cDNA molecule complementary to the template and / or to the acceptor nucleic acid molecule. In some embodiments, the method for preparing a cDNA library comprises mixing, in the presence of nucleotides (e.g., dNTPs), a primer or one or more primer(s), a template, a modified reverse transcriptase, and an acceptor nucleic acid molecule (e.g., acceptor RNA, DNA, or a combination thereof) under conditions sufficient to generate a cDNA molecule complementary to the template and / or to the acceptor nucleic acid molecule. In some embodiments, the enzyme (e.g., modified reverse transcriptase) generates a continuous cDNA molecule by migrating from the template to the acceptor nucleic acid molecule. In some embodiments, template jumping is independent of sequence identity between the template and the acceptor nucleic acid molecule. In some embodiments the method further comprises amplifying the cDNA molecule to generate a cDNA library. In some embodiments, step (a) and step (b) are done at the same time. In some embodiments, step (a) comprises step (b) (e.g., step (a) and step (b) are merged into one step). In some embodiments, the mixing step or at least one of step (a) and / or step (b) further comprises addition of a hot start thermostable polymerase. In some embodiments, the method described herein is performed in a single tube. In some embodiments, the method described herein further comprises a polymerase chain reaction (PCR) amplification reaction. In some embodiments, the PCR amplification reaction is performed in a single tube (e.g., the same one tube used in or from the mixing step, or in or from steps (a) and (b)). In some embodiments, all the steps of the method described herein is performed in a single tube.

[0092] Described herein are methods for preparing a cDNA and / or DNA library comprising: mixing, in the presence of nucleotides (e.g., dNTPs), a fragment or degraded template (e.g., a nucleic acid fragment), a primer, a modified reverse transcriptase, and an acceptor nucleic acid molecule under conditions sufficient to generate a nucleic acid (e.g., cDNA and / or DNA) molecule. In some embodiments, the acceptor nucleic acid molecule comprises a modified nucleotide. In some embodiments, the primer extension stops at the modified nucleotide. In some embodiments, the modified reverse transcriptase comprises at least one improved enzyme property relative to a wild type or unmodified reverse transcriptase. In some embodiments, the primer is an RNA R2 primer. In some embodiments, the method further comprises amplifying the nucleic acid (e.g., cDNA and / or DNA) molecule to generate a cDNA library. In some embodiments, the method for preparing a cDNA and / or DNA and / or nucleic acid molecule is via template jumping.

[0093] Described herein are methods for preparing a cDNA and / or DNA library comprising: mixing, in the presence of nucleotides (e.g., dNTPs), a fragment or degraded template (e.g., a nucleic acid fragment), a donor complex, a modified reverse transcriptase, and an acceptor nucleic acid molecule under conditions sufficient to generate a nucleic acid (e.g., cDNA and / or DNA) molecule. In some embodiments, the acceptor nucleic acid molecule comprises a modified nucleotide. In some embodiments, the primer extension stops at the modified nucleotide. In some embodiments, the modified reverse transcriptase comprises at least one improved enzyme property relative to a wild type or unmodified reverse transcriptase. In some embodiments, the donor complex comprises a template and a primer. In some embodiments, the donor complex is a donor R2 complex. In some embodiments, the donor R2 complex comprises an RNA R2 primer. In some embodiments, the method further comprises amplifying the nucleic acid (e.g., cDNA and / or DNA) molecule to generate a cDNA and / or DNA library. In some embodiments, the method for preparing a cDNA and / or DNA and / or nucleic acid molecule molecule is via template jumping.

[0094] In some embodiments, the method described herein may comprise a donor complex. In some embodiments, the donor complex comprises a template and a primer. In some embodiments, the method described herein may comprise a template. In some embodiments, the template is a fragmented and / or degraded template. In some embodiments, the template is not fragmented. In some embodiments, the template is RNA, DNA, or a combination of DNA and RNA. In some embodiments, the RNA is mRNA. In some embodiments, the template is mRNA.

[0095] Described herein are methods for preparing a library for sequencing comprising: (a) obtaining a sample with cell-free nucleic acid from a subject; and (b) adding a modified reverse transcriptase enzyme, a template (e.g., a nucleic acid template), nucleotides, an acceptor nucleic acid molecule, and one or more primer(s) to the nucleic acid. In some embodiments, the method further comprises conducting an amplification reaction on the cell-free nucleic acid (cf nucleic acid) derived from the sample to produce a plurality of amplicons. In some embodiments, the amplification reaction comprises 35 or fewer amplification cycles. In some embodiments, the method comprises producing a library for sequencing. In some embodiments, the library comprises a plurality of amplicons. In some embodiments, the modified reverse transcriptase is capable of template jumping and / or comprises at least one improved enzyme property relative to a wild type or unmodified reverse transcriptase. In some embodiments, the nucleic acid is DNA, RNA, or a combination of RNA and DNA.

[0096] Described herein is a method for preparing a complementary deoxyribonucleic acid (cDNA) molecule using template jumping, comprising mixing, in a single tube, a primer or one or more primer(s), a messenger RNA (mRNA) template, nucleotides, a modified reverse transcriptase, an acceptor nucleic acid molecule, and a catalytic metal under conditions sufficient to generate a continuous cDNA molecule. In some embodiments, the continuous cDNA molecule is complementary to the mRNA template and / or to the acceptor nucleic acid molecule. In some embodiments, the modified reverse transcriptase comprises at least one improved enzyme property relative to a wild type or unmodified reverse transcriptase. In some embodiments, a continuous cDNA molecule is produced. In some embodiments, the modified reverse transcriptase undergoes migration from the template to the acceptor nucleic acid molecule.

[0097] Described herein is a method for preparing a library for sequencing comprising mixing, in a single tube, a cell-free nucleic acid, a modified reverse transcriptase enzyme, a template, nucleotides, an acceptor nucleic acid molecule, a catalytic metal, and one or more primer(s), under conditions sufficient to generate a library. In some embodiments, the modified reverse transcriptase comprises at least one improved enzyme property relative to a wild type or unmodified reverse transcriptase.

[0098] In some embodiments, the nucleic acid molecule comprises an unknown nucleic acid sequence. In some embodiments, the template comprises an unknown nucleic acid sequence. In some embodiments, the migration from the template to the acceptor nucleic acid molecule is independent of sequence identity between the template and the acceptor nucleic acid molecule. In some embodiments, the acceptor nucleic acid molecule comprises a modified nucleotide that may cause primer extension to stop. In some embodiments, the cell-free nucleic acid is cell-free DNA (cfDNA), circulating tumor DNA (ctDNA), and / or formalin-fixed, paraffin-embedded DNA (FFPE DNA), or combinations thereof.

[0099] In some embodiments, a hot start thermostable polymerase may be added to a method described herein at or prior to any step of the method and / or at the same time that a mixing step takes place. For example, a hot start thermostable polymerase may be added at the same time that the modified reverse transcriptase is added to the reaction. The hot start thermostable polymerase may be added at the same time that the acceptor nucleic acid molecule is added, and / or at the same time that the template, and / or primer, and / or reverse transcriptase, and / or nucleotides is added to the reaction tube. In some embodiments, the hot start thermostable polymerase is added prior to the start of the PCR reaction. In some embodiments, the hot start thermostable polymerase is added prior to or at the same time as the RT reaction. In some embodiments, the hot start thermostable polymerase is hot start taq polymerase. Amplification of target nucleic acids can occur on a bead. In some embodiments, amplification does not occur on a bead. Amplification can be by isothermal amplification, e.g., isothermal linear amplification. In some embodiments, a hot start PCR can be performed wherein the reaction is heated to 95 °C e.g., for two minutes prior to addition of a polymerase or the polymerase can be kept inactive until a first heating step in cycle 1. Hot start PCR can be used to minimize nonspecific amplification.

[0100] In some embodiments, the method described herein is performed in a single tube. In some embodiments, all the steps of the method described herein is performed in a single tube. In some embodiments, the method (from start to finish) is performed in a single tube. In some embodiments, the same tube used for the RT reaction is used for the PCR amplification reaction.

[0101] In some embodiments, the PCR amplification is performed at a temperature sufficient to inactivate the reverse transcriptase enzyme. In some embodiments, the PCR amplification is performed at a temperature sufficient to activate the hot start thermostable polymerase.

[0102] Described herein aremethods of amplifying a cell-free nucleic acid molecule from a sample. In some embodiments, the sample is a biological sample. In some embodiments, the cell-free nucleic acid molecule is subjected to nucleic acid amplification comprising a reverse transcriptase (e.g., modified reverse transcriptase). In some embodiments, the cell-free nucleic acid molecule is subjected to nucleic acid amplification comprising a reverse transcriptase (e.g., modified reverse transcriptase) under conditions that amplify the nucleic acid molecule at a specified processivity. In some embodiments the processivity is of at least about 80% per base, at least about 81% per base, at least about 82% per base, at least about 83% per base, at least about 84% per base, at least about 85% per base, at least about 86% per base, at least about 87% per base, at least about 88% per base, at least about 89% per base, at least about 90% per base, at least about 91% per base, at least about 92% per base, at least about 93% per base, at least about 94% per base, at least about 95% per base, at least about 96% per base, at least about 97% per base, at least about 98% per base, at least about 99% per base, or at least about 100% per base. In some embodiments, the processivity is performed at a temperature of about or at most about or at least about 12 °C, of about or at most about or at least about 13 °C, of about or at most about or at least about 14 °C, of about or at most about or at least about 15 °C, of about or at most about or at least about 16 °C, of about or at most about or at least about 17 °C, of about or at most about or at least about 18 °C, of about or at most about or at least about 19 °C, of about or at most about or at least about 20 °C, of about or at most about or at least about 21 °C, of about or at most about or at least about 22 °C, of about or at most about or at least about 23 °C, of about or at most about or at least about 24 °C, of about or at most about or at least about 25 °C, of about or at most about or at least about 26 °C, of about or at most about or at least about 27 °Cof about or at most about or at least about 28 °C, of about or at most about or at least about 29 °C, of about or at most about or at least about 30 °C, of about or at most about or at least about 31 °C, of about or at most about or at least about 32 °C, of about or at most about or at least about 33 °C, of about or at most about or at least about 34 °C, of about or at most about or at least about 35 °C, of about or at most about or at least about 36 °C, of about or at most about or at least about 37 °C, of about or at most about or at least about 38 °C, of about or at most about or at least about 39 °C, of about or at most about or at least about 40 °C, of about or at most about or at least about 45 °C, of about or at most about or at least about 50 °C, of about or at most about or at least about 60 °C, of about or at most about or at least about 70 °C, of about or at most about or at least about 80 °C, of about or at most about or at least about 8 °C. In some embodiments the processivity is of at least about 80% per base, at least about 81% per base, at least about 82% per base, at least about 83% per base, at least about 84% per base, at least about 85% per base, at least about 86% per base, at least about 87% per base, at least about 88% per base, at least about 89% per base, at least about 90% per base, at least about 91% per base, at least about 92% per base, at least about 93% per base, at least about 94% per base, at least about 95% per base, at least about 96% per base, at least about 97% per base, at least about 98% per base, at least about 99% per base, or at least about 100% per base, at a temperature of about or at most about or of at least about 30 °C, or of about or at most about or of at least about 12 °C, of about or at most about or of at least about 45 °C, of about or at most about or of at least about 35 °C. In some embodiments, the reverse transcriptase is a non-LTR retrotransposon or a modified non-LTR retrotransposon. In some embodiments, the reverse transcriptase is an R2 reverse transcriptase or a modified R2 reverse transcriptase. In some embodiments, the reverse transcriptase is an R2 non-LTR retrotransposon or a modified R2 non-LTR retrotransposon.

[0103] Described herein are methods for preparing a complementary deoxyribonucleic acid (cDNA) library and / or a DNA library from a plurality of single cells. In some embodiments, the method comprises the steps of: releasing nucleic acid from each single cell to provide a plurality of individual nucleic acid samples. In some embodiments, the nucleic acid in each individual nucleic acid sample is from a single cell. In some embodiments, the method further comprises annealing the nucleic acid template to one or more primer(s). In some embodiments, the method further comprises mixing the nucleic acid template annealed to one or more primer(s) with an acceptor template (or an acceptor nucleic acid molecule) and a modified reverse transcriptase, in the presence of nucleotides, under conditions effective for producing a cDNA and / or a DNAmolecule. In some embodiments, the modified reverse transcriptase is capable of template jumping and / or comprises at least one improved enzyme property relative to a wild type or unmodified reverse transcriptase. In some embodiments, the method further comprises amplifying the cDNA molecule and / or DNA molecule to generate a cDNA and / or DNA library.

[0104] Described herein are methods of detecting a nucleic acid molecule. In some embodiments, the method comprises mixing a sample comprising a nucleic acid molecule with an acceptor template (or an acceptor nucleic acid molecule), a modified reverse transcriptase, a primer, and nucleotides, under conditions effective for generating a nucleic acid molecule. In some embodiments, the modified reverse transcriptase comprises at least one improved enzyme property relative to a wild type or unmodified reverse transcriptase. In some embodiments, the acceptor template (or an acceptor nucleic acid molecule) comprises at least one modified nucleotide. In some embodiments, the modified nucleotide may cause primer extension to stop. In some embodiments, the method further comprises amplifying the nucleic acid molecule.

[0105] Described herein are methods of detecting, diagnosing, and / or prognosing a disease (e.g., cancer) in a subject comprising: (a) obtaining sequence information of a nucleic acid sample (e.g., a cell-free nucleic acid sample) derived from a subject and (b) using the sequence information derived from step (a) to detect circulating tumor nucleic acid in the sample. In some embodiments, obtaining sequence information according to step (a) comprises using one or more adaptor(s). In some embodiments, the one or more adaptor(s) comprises a molecular barcode. An adaptor can comprise one or more end modifications. An adaptor can comprise one 5' phosphate. An adaptor can comprise two 5' phosphates. An adaptor can comprise one 3' hydroxyl. An adaptor can comprise two 3' hydroxyls. An adaptor can lack a 3' hydroxyl.

[0106] In some embodiments, the molecular barcode comprises a randomer sequence. In some embodiments, the method is capable of detecting cell-free nucleic acid that is less than or equal to about 0.75%, 0.50%, 0.25%, 0.1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, 0.05%, 0.01%, 0.009%, 0.008%, 0.007%, 0.006%, 0.005%, 0.004%, 0.003%, 0.002%, 0.001%, 0.0005%, or 0.00001%, 1%, 1.75%, 1.5%, 1.25%, 2%, 3%, 4%, 5%, 6%, 8%, 9%, 10%, 11%, 12%, 13%, 14% 15%, 16%, 17%, 18%, 19%, 20%, 22%, 25%, 27%, 30%, 32%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% of total cell-free nucleic acid. In some embodiments, the method is capable of detecting circulating tumor nucleic acid that is less than or equal to about 0.75%, 0.50%, 0.25%, 0.1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, 0.05%, 0.01%, 0.009%, 0.008%, 0.007%, 0.006%, 0.005%, 0.004%, 0.003%, 0.002%, 0.001%, 0.0005%, or 0.00001%, 1%, 1.75%, 1.5%, 1.25%, 2%, 3%, 4%, 5%, 6%, 8%, 9%, 10%, 11%, 12%, 13%, 14% 15%, 16%, 17%, 18%, 19%, 20%, 22%, 25%, 27%, 30%, 32%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, or 100% of total circulating nucleic acid. In some embodiments, the method is capable of detecting a percentage of circulating tumor nucleic acid (ct nucleic acid) that is less than or equal to 1.75%, 1.5%, 1.25%, 1%, 0.75%, 0.50%, 0.25%, 0.1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%, 0.1%, 0.05%, 0.01%, 0.009%, 0.008%, 0.007%, 0.006%, 0.005%, 0.004%, 0.003%, 0.002%, 0.001%, 0.0005%, or 0.00001% of the total cell-free nucleic acid. In some embodiments, the sequence information comprises information related to at least about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 35, 40, 50, 70, 80, 100, 200, or 300 genomic regions. In some embodiments, the sequence information comprises information related to partially all, mostly all, or all genome sequencing. In some embodiments, concentrations as low as 50 ng of cfDNA may provide for full genome sequencing.

[0107] In some embodiments, the method described herein may be used to determine the presence of a disease (e.g., cancer) in a subject. In some embodiments, determining the presence of cancer in a subject comprises obtaining a sample from a subject and detecting a nucleic acid molecule (e.g., nucleic acid fragment) in the sample according to any of the methods described herein. In some embodiments, determining the presence of a disease (e.g., cancer) in a subject comprises amplifying and / or sequencing the nucleic acid molecule. In some embodiments, the presence of a nucleic acid molecule is indicative of cancer. In some embodiments, the presence of a nucleic acid molecule is indicative of a prenatal condition. In some embodiments, the nucleic acid molecule and / or template comprises an unknown sequence. In some embodiments, the sample is a biological sample. In some embodiments, the biological sample comprises circulating tumor DNA. In some embodiments, the biological sample comprises a tissue sample.

[0108] In some embodiments, the method described herein comprises detecting an amplicon generated by the amplification primers, wherein the presence of the amplicon determines whether the modified reverse transcriptase is present in the sample.

[0109] In some embodiments, the method described herein comprises providing a prenatal diagnosis based on the presence or absence of a nucleic acid molecule (e.g., cDNA molecule).

[0110] Described herein isa kit of producing a nucleic acid molecule (e.g., cDNA molecule) comprising: one or more primer(s), nucleotides, at least one modified reverse transcriptase, a template, and instructions for performing any of the methods described herein. In some embodiments, a kit can be used for detecting nucleic acid comprising a nucleic acid template (e.g., a DNA template), at least one modified reverse transcriptase, nucleotides, and instructions for performing any of the methods described herein. In some embodiments, the modified reverse transcriptase present in the kit or to be used with the kit has activity and / or is capable of template jumping at a temperature equal to or less than about or more than about 4 °C, 8 °C, 12 °C, 13 °C, 14 °C, 15 °C, 16 °C, 17 °C, 18 °C, 19 °C, 20 °C, 21 °C, 22 °C, 23 °C, 24 °C, 25 °C, 26 °C, 27 °C, 28 °C, 29 °C, 30 °C, 31 °C, 32 °C, 33 °C, 34 °C, 35 °C, 36 °C, 37 °C, 38 °C, 39 °C, 40 °C, 41 °C, 42 °C, 45 °C, 46 °C, 47 °C, 48 °C, 49 °C, 50 °C, 52 °C, 55 °C, or 60 °C. In some embodiments, the nucleic acid and / or the template (e.g., nucleic acid template, DNA, or RNA) is present at a concentration as low as about 50 femtomolar, as low as about 60 femtomolar, as low as about 70 femtomolar, as low as about 75 femtomolar, as low as about 80 femtomolar, as low as about 90 femtomolar, as low as about 100 femtomolar, as low as about 120 femtomolar, as low as about 150 femtomolar, as low as about 200 femtomolar, as low as about 250 femtomolar, as low as about 300 femtomolar, as low as about 350 femtomolar, as low as about 400 femtomolar, as low as about 500 femtomolar, as low as about 550 femtomolar, as low as about 600 femtomolar, as low as about 700 femtomolar, or as low as about 800 femtomolar. In some embodiments, a kit may comprise one or more primer(s), and / or a template annealed to a primer. Also described herein is a kit of producing modified enzymes, modified reverse transcriptases, or modified polypeptides. In some embodiments, the kit includes a PCR step and / or components to use for PCR.

[0111] In some embodiments, the kit described herein is a kit for detecting nucleic acid comprising a template, at least one modified reverse transcriptase, nucleotides, and instructions to perform the method described herein. In some embodiments, the nucleic acid is present at a concentration of at least about 50 femtomolar, at least about 20 femtomolar, at least about 100 femtomolar, or greater than about 1000 femtomolar.

[0112] Any method described herein may further comprise detecting at least one amplicon generated by the amplification primers. In some embodiments, the presence of at least one amplicon indicates the presence of at least one modified reverse transcriptase in a sample.

[0113] In some embodiments, any of the methods described herein does not comprise a purification step. In some embodiments, any of the methods described herein comprises at least one purification step. In some embodiments, any of the methods of described herein comprises at least two purification steps. In some embodiments, any of the methods described herein comprise at least three, at least four, at least five, at least six, at least seven, at least eight, at least nine, at least ten, at least fifteen, or at least twenty purification steps.

[0114] Described herein is a method for preparing a library for sequencing.

[0115] In some embodiments, the modified reverse transcriptase is a modified non-retroviral reverse transcriptase. In some embodiments, the modified reverse transcriptase is a modified non-LTR retrotransposon. In some embodiments, the modified reverse transcriptase is a modified R2 reverse transcriptase.

[0116] In some embodiments, the variants or modified enzymes or non-naturally occurring enzymes or modified polypeptides have / has improved enzyme property compared to the unmodified, wild type or naturally occurring enzyme or polypeptide. In some embodiments, the improved enzyme property is selected from at least one of the following: increased stability (e.g., increased thermostability), increased specific activity, increased protein expression, improved purification, improved processivity, improved strand displacement, increased template jumping, and improved fidelity. In some embodiments, the term stability may include thermal stability, storage stability, and pH stability. In some embodiments, specific activity is a measurement of the enzymatic activity (in units) of the protein or enzyme relative to the total amount of protein or enzyme used in a reaction. In some embodiments, specific activity is measured based on the ability of the enzyme to produce cDNA molecule. In some embodiments, the specific activity is measured in U / mg protein determined based on a primer extension reaction. In some embodiments, the altered or improved property may be characterized by a Performance Index (PI), where the PI is a ratio of performance of the variant, the modified enzyme, or the non-naturally occurring enzyme compared to the wild-type or compared to a naturally occurring enzyme or protein. The term "performance index (PI)" may refer to the ratio of performance of a variant polypeptide to a parent polypeptide or of a modified enzyme to an unmodified enzyme (e.g., reverse transcriptase) or of a non-naturally occurring enzyme to a naturally-occurring enzyme for a specified performance characteristic. In some embodiments, the specified performance or enzyme property characteristic may include, but is not limited to, stability (e.g., thermostability), specific activity, protein expression, purification, processivity, strand displacement, end-to-end template jumping, and / or fidelity. In some embodiments, the PI is greater than about 0.5, while in other embodiments, the PI is about 1 or is greater than about 1. In some embodiments, the variant polypeptide, modified enzyme (e.g., modified reverse transcriptase), or the non-naturally occurring enzyme comprises a modification at one or more amino acid positions. In some embodiments, the modified enzyme or the non-naturally occurring enzyme has a performance index (PI) that is equal to or greater than about 0.1, equal to or greater than about 0.2, equal to or greater than about 0.3, equal to or greater than about 0.4, equal to or greater than about 0.5, equal to or greater than about 0.6, equal to or greater than about 0.7, equal to or greater than about 0.8, equal to or greater than about 0.9, equal to or greater than about 1, equal to or greater than about 1.2, equal to or greater than about 1.5, equal to or greater than about 2, equal to or greater than about 2.5, equal to or greater than about 3, equal to or greater than about 3.5, equal to or greater than about 4, equal to or greater than about 4.5, equal to or greater than about 5, equal to or greater than about 5.5, equal to or greater than about 6, equal to or greater than about 6.5, equal to or greater than about 7, equal to or greater than about 8, equal to or greater than about 9, equal to or greater than about 10, equal to or greater than about 50, equal to or greater than about 75, equal to or greater than about 100, equal to or greater than about 500, equal to or greater than about 1000. In some embodiments, the variant or modified enzyme has a performance index (PI) from about 0.1 to about 1, from about 0.5 to about 1, from about 0.1 to about 2, from about 1 to about 2, from about 0.5 to about 2, from about 0.5 to about 10, from about 1 to about 10, from about 0.1 to about 10, from about 1 to about 5, from about 0.5 to about 5, from about 0.5 to about 20, from about 0.3 to about 20, from about 5 to about 10, from about 1.5 to about 10, from about 1.5 to about 50, from about 1 to about 50, from about 1.5 to about 100, from about 1.5 to about 75, from about 4 to about 10, from 3 to about 10, from about 3 to about 25, from about 3 to about 50, from about 2 to about 20, from about 2 to about 100, from about 2 to about 1000, from about 1 to about 1000. In some embodiments, the performance index is determined for protein expression. In some embodiments, the performance index is determined for at least one characteristic that improves enzyme property. In some embodiments, the performance index is determined for purification. In some embodiments, the performance index is determined for stability (e.g., thermostability). In some embodiments, the performance index is determined for specific activity. In some embodiments, the performance index is determined for processivity. In some embodiments, the performance index is determined for strand displacement. In some embodiments, the performance index is determined for template jumping. In some embodiments, the performance index is determined for fidelity. In some embodiments, the characteristic that improves enzyme property is selected from the group consisting of increased thermal stability, increased specific activity, and increased protein expression. In some embodiments, the performance index is performed at 30 °C. In some embodiments, the enzyme property is analyzed at 30 °C. In some embodiments, the enzyme property, stability (e.g., thermostability), specific activity, protein expression, purification, processivity, strand displacement, template jumping, and / or fidelity is performed at 30 °C. In some embodiments, the performance index for measuring enzyme property, is performed at a specific temperature. In some embodiments, the temperature is from about 25 °C to about 42 °C. In some embodiments, the temperature is from about 8 °C to about 50 °C. In some embodiments, the performance index for measuring enzyme property may be carried out at a temperature ranging from about from about 8 °C to about 50 °C, from about 12 °C to about 42 °C, 25 °C to about 42 °C, from about 25 °C to about 40 °C, from about 28 °C to about 38 °C, from about 30 °C to about 38 °C, from about 35 °C to about 37 °C, from about 27 °C to about 38 °C, from about 27 °C to about 37 °C, from about 26 °C to about 42 °C, from about 25 °C to about 38 °C, from about 27 °C to about 38 °C, from about 29 °C to about 38 °C, from about 29 °C to about 32 °C. In some embodiments, the performance index for measuring enzyme property may be carried out at a temperature that is equal to or lower than about 8 °C, equal to or lower than about 12 °C, equal to or lower than about 20 °C, equal to or lower than about 4 °C, equal to or lower than about 55 °C, equal to or lower than about 37 °C, equal to or lower than about 25 °C, equal to or lower than about 28 °C, equal to or lower than about 30 °C, equal to or lower than about 32 °C, equal to or lower than about 34 °C, equal to or lower than about 35 °C, equal to or lower than about 36 °C, equal to or lower than about 33 °C, equal to or lower than about 31 °C, equal to or lower than about 60 °C, equal to or lower than about 38 °C, equal to or lower than about 39 °C, equal to or lower than about 40 °C, equal to or lower than about 41 °C, equal to or lower than about 42 °C, equal to or lower than about 50 °C. In some embodiments, the temperature may range from about 25 °C to about 80 °C.

[0117] In some embodiments, the specific activity of the modified enzyme is from about 5 units / mg to about 140,000 units / mg, from about 5 units / mg to about 125,000 units / mg, from about 50 units / mg to about 100,000 units / mg, from about 100 units / mg to about 100,000 units / mg, from about 250 units / mg to about 100,000 units / mg, from about 500 units / mg to about 100,000 units / mg, from about 1000 units / mg to about 100,000 units / mg, from about 5000 units / mg to about 100,000 units / mg, from about 10,000 units / mg to about 100,000 units / mg, from about 25,000 units / mg to about 75,000 units / mg. In some embodiments, the ranges of specific activities include a specific activity of from about 20,000 units / mg to about 140,000 units / mg, a specific activity from about 20,000 units / mg to about 130,000 units / mg, a specific activity from about 20,000 units / mg to about 120,000 units / mg, a specific activity from about 20,000 units / mg to about 110,000 units / mg, a specific activity from about 20,000 units / mg to about 100,000 units / mg, a specific activity from about 20,000 units / mg to about 90,000 units / mg, a specific activity from about 25,000 units / mg to about 140,000 units / mg, a specific activity from about 25,000 units / mg to about 130,000 units / mg, a specific activity from about 25,000 units / mg to about 120,000 units / mg, a specific activity from about 25,000 units / mg to about 110,000 units / mg, a specific activity from about 25,000 units / mg to about 100,000 units / mg, and a specific activity from about 25,000 units / mg to about 90,000 units / mg. In some embodiments, the lower end of the specific activity range may vary from 30,000, 35,000, 40,000, 45,000, 50,000, 55,000, 60,000, 65,000, 70,000, 75,000, and 80,000 units / mg. In some embodiments, the upper end of the range may vary from 150,000, 140,000, 130,000, 120,000, 110,000, 100,000, and 90,000 units / mg.

[0118] In some embodiments, the sample is a biological sample. In some embodiments, the biological sample comprises a circulating tumor DNA. In some embodiments, the biological sample comprises a tissue sample. In some embodiments, the nucleic acid is from a sample. In some embodiments, the sample is a liquid biopsy sample. In some embodiments, a sample may be an RNA sample. In some embodiments, an RNA sample may be used for various purposes, including PCR, ligation, transcriptome analysis, microarray analysis, northern analysis, and cDNA library construction. In some embodiments, the methods described herein are directed to methods for amplifying cDNA libraries from low quantities of cells and / or single cells in suitable quantity and quality for transcriptome analysis through, for example, sequencing or microarray analysis.

[0119] In some embodiments, the nucleic acid and / or a template is of an unknown sequence. In some embodiments, the nucleic acid and / or a template is RNA, DNA, or a combination of RNA and DNA. In some embodiments, the RNA is mRNA. In some embodiments, the mRNA comprises internal priming. In some embodiments, the nucleic acid may be a fragmented nucleic acid and / or a degraded nucleic acid. In some embodiments, the template may be a fragmented template and / or a degraded template. In some embodiments, the nucleic acid may be a non-fragmented nucleic acid and / or a non-degraded nucleic acid. In some embodiments, the template may be a non-fragmented template and / or a non-degraded template. In some embodiments, the nucleic acid and / or template is indicative of a disease. In some embodiments, the nucleic acid and / or template is indicative of cancer. In some embodiments, the nucleic acid is equal to or less than about 0.01 micromolar. In some embodiments, the nucleic acid is between about 0.1nM to about 100nM. In some embodiments, the nucleic acid is equal to or less than about 500 femtomolar.

[0120] In some embodiments, the RNA is obtained from a source selected from the group consisting of single cells, cultured cells, tissues, RNA transcription-based amplified RNA (such as TTR-amplified RNA or other DNA-dependent RNA polymerase transcribed RNA), RNA-promoter-driven transcribed RNA, aRNA, aRNA-amplified RNA, single-cell mRNA library, isolated mRNA, RNA contained within cells, and combinations of RNA sources. In some embodiments, the RNA is prepared from a plurality of fixed cells, wherein said fixed cells are protected from RNA degradation and also subjected to permeabilisation for enzyme penetration. In some embodiments, the fixed cells are obtained from fixative-treated cultural cells, frozen fresh tissues, fixative-treated fresh tissues or paraffin-embedded tissues on slides.

[0121] In some embodiments, the RNA molecule can be the product of in vitro synthesis or can have been isolated from cells or tissues (Ausubel, et. al., Short Protocols in Molecular Biology, 3rd ed., Wiley, 1995). Cells and tissues suitable for use in obtaining RNA useful in the practice of the methods described herein may include both animal cells and plant cells. In some embodiments, the cells include mammalian cells and insect cells. RNA may also be isolated from prokaryotic cells such as bacteria.

[0122] In some embodiments, the template is RNA, DNA, or a combination of RNA and DNA. In some embodiments, the template may be a fragmented template and / or a degraded template. In some embodiments, the template is not degraded and / or fragmented. In some embodiments, the RNA is mRNA. In some embodiments, the template is an RNA template. In some embodiments, the template is a DNA template. In some embodiments, the template is a DNA and / or RNA template. In some embodiments, the template is a mixture of DNA and RNA. In some embodiments, the RNA comprises any type of RNA (e.g., one or more of rRNA, tRNA, mRNA, and / or snRNA). In some embodiments the RNA comprises a mixture of at least one type of RNA. In some embodiments, the DNA can comprise a mixture of, or at least one of, genomic DNA or nuclear DNA, mitochondrial DNA, Y-line DNA, autosomal DNA, ribosomal DNA, or a combination thereof. In some embodiments, the template is a polymer of any length. In some embodiments, the template is from about 20 bases to about 100 bases, from about 30 bases to about 500 bases, from about 30 bases to about 1000 bases, from about 50 bases to about 300 bases, about 100 bases to about 600 bases, about 200 bases to about 800 bases, about 200 bases to about 600 bases, about 100 bases to about 2000 bases, about 100 bases and about 2500 bases, about 200 bases to about 5000 bases, about 200 bases to about 1000 bases, about 200 to about 10000 bases. In some embodiments, the template is at least about 10 bases, at least about 20 bases, at least about 30 bases, at least about 40 bases, at least about 50 bases, at least about 60 bases, at least about 70 bases, at least about 80 bases, at least about 90 bases, at least about 100 bases, at least about 150 bases, at least about 200 bases, at least about 250 bases, at least about 300 bases, at least about 350 bases, at least about 400 bases, at least about 450 bases, at least about 500 bases, at least about 550 bases, at least about 600 bases, at least about 650 bases, at least about 700 bases, at least about 750 bases, at least about 800 bases, at least about 850 bases, at least about 900 bases, at least about 950 bases, at least about 1000 bases, at least about 1100 bases, at least about 1200 bases, at least about 1300 bases, at least about 1400 bases, at least about 1500 bases, at least about 1700 bases, at least about 2000 bases, at least about 2200 bases, at least about 2500 bases, at least about 2700 bases, at least about 3000, at least about 3500 bases, at least about 4000 bases, at least about 4500 bases, at least about 5000 bases, at least about 10,000 bases, or at least about 50,000 bases. In some embodiments, the template is about or at least about or at most about 10 bases, about or at least about or at most about 20 bases, about or at least about or at most about 30 bases, about or at least about or at most about 40 bases, about or at least about or at most about 50 bases, about or at least about or at most about 60 bases, about or at least about or at most about 70 bases, about or at least about or at most about 80 bases, about or at least about or at most about 90 bases, about or at least about or at most about 100 bases, about or at least about or at most about 150 bases, about or at least about or at most about 200 bases, about or at least about or at most about 250 bases, about or at least about or at most about 300 bases, about or at least about or at most about 350 bases, about or at least about or at most about 400 bases, about or at least about or at most about 450 bases, about or at least about or at most about 500 bases, about or at least about or at most about 550 bases, about or at least about or at most about 600 bases, about or at least about or at most about 650 bases, about or at least about or at most about 700 bases, about or at least about or at most about 750 bases, about or at least about or at most about 800 bases, about or at least about or at most about 850 bases, about or at least about or at most about 900 bases, about or at least about or at most about 950 bases, about or at least about or at most about 1000 bases, about or at least about or at most about 1100 bases, about or at least about or at most about 1200 bases, about or at least about or at most about 1300 bases, about or at least about or at most about 1400 bases, about or at least about or at most about 1500 bases, about or at least about or at most about 1700 bases, about or at least about or at most about 2000 bases, about or at least about or at most about 2200 bases, about or at least about or at most about 2500 bases, about or at least about or at most about 2700 bases, about or at least about or at most about 3000, about or at least about or at most about 3500 bases, about or at least about or at most about 4000 bases, about or at least about or at most about 4500 bases, about or at least about or at most about 5000 bases, about or at least about or at most about 10,000 bases, or about or at least about or at most about 50,000 bases. In some embodiments, the template DNA may be a double-stranded DNA template (dsDNA template) or a single-stranded DNA template (ssDNA template). In some embodiments, the template RNA may be a double-stranded RNA template (dsRNA template) or a single-stranded RNA template (ssRNA template).

[0123] In some embodiments, the template is from a single cell. In some embodiments, the template is from a plurality of cells. In some embodiments, the template comprises low copy number DNA, or RNA, or a combination of DNA and / or RNA. In some embodiments, low copy number refers to samples that contain equal to or less than about 250 picograms (e.g. 100 picograms) of for example the template and / or DNA and / or RNA and / or a mixture of DNA and RNA. In some embodiments, the RNA can comprise at least one of messenger RNA (mRNA), transfer RNA, transfer-messenger RNA, ribosomal RNA, antisense RNA, small nuclear RNA (snRNA), small nucleolar RNA (snoRNA), micro-RNA (miRNA), small interfering RNA (siRNA), or any combination thereof. In some embodiments, the template is from a sample. In some embodiments, the total amount of template is the total amount of template in a sample. In some embodiments, the total amount of template is the total amount of template in a reaction mixture. In some embodiments, the total amount of template is the total amount of template in one pot (e.g., single vessel). In some embodiments, the total amount of the template is from about 1 femtomolar (fM) to about 100 micromolar, from about 40 femtomolar to about 0.01 micromolar, from about 50 femtomolar to about 500 femtomolar, from about 50 femtomolar to about 0.01 micromolar, from about 50 femtomolar to about 0.1 micromolar, from about 50 femtomolar to about 500 picomolar, from about 50 femtomolar to about 500 nanomolar, from about 50 femtomolar to about 500 micromolar, from about 50 femtomolar to about 1 picomolar, from about 40 femtomolar to about 1 nanomolar, from about 1 femtomolar to about 1 picolomar, from about 0.0001 micromolar to about 0.01 micromolar, from about 0.0001 micromolar to about 0.1 micromolar, or from about 0.1nM to about 100nM. In some embodiments, the total about of template is equal to or at least about or lower than about 1000 micromolar, equal to or at least about or lower than about 500 micromolar, equal to or at least about or lower than about 250 micromolar, equal to or at least about or lower than about 100 micromolar, equal to or at least about or lower than about 50 micromolar, equal to or at least about or lower than about 25 micromolar, equal to or at least about or lower than about 10 micromolar, equal to or at least about or lower than about 1 micromolar, equal to or at least about or lower than about 0.1 micromolar, equal to or at least about or lower than about 0.01 micromolar, equal to or at least about or lower than about 0.001 micromolar, equal to or at least about or lower than about 0.0001 micromolar, equal to or at least about or lower than about 2000 nanomolar, equal to or at least about or lower than about 500 nanomolar, equal to or at least about or lower than about 250 nanomolar, equal to or at least about or lower than about 200 nanomolar, equal to or at least about or lower than about 50 nanomolar, equal to or at least about or lower than about 25 nanomolar, equal to or at least about or lower than about 20 nanomolar, equal to or at least about or lower than about 2 nanomolar, equal to or at least about or lower than about 0.2 nanomolar, equal to or at least about or lower than about 0.01 nanomolar, equal to or at least about or lower than about 0.001 nanomolar, equal to or at least about or lower than about 0.0001 nanomolar, equal to or at least about or lower than about 3000 picomolar, equal to or at least about or lower than about 500 picomolar, equal to or at least about or lower than about 250 picomolar, equal to or at least about or lower than about 300 picomolar, equal to or at least about or lower than about 50 picomolar, equal to or at least about or lower than about 25 picomolar, equal to or at least about or lower than about 30 picomolar, equal to or at least about or lower than about 3 picomolar, equal to or at least about or lower than about 0.3 picomolar, equal to or at least about or lower than about 0.01 picomolar, equal to or at least about or lower than about 0.001 picomolar, equal to or at least about or lower than about 0.0001 picomolar, equal to or at least about or lower than about 5000 femtomolar, equal to or at least about or lower than about 500 femtomolar, equal to or at least about or lower than about 250 femtomolar, equal to or at least about or lower than about 50 femtomolar, equal to or at least about or lower than about 25 femtomolar, equal to or at least about or lower than about 10 femtomolar, equal to or at least about or lower than about 1 femtomolar, equal to or at least about or lower than about 0.1 femtomolar, equal to or at least about or lower than about 0.01 femtomolar, equal to or at least about or lower than about 0.001 femtomolar, equal to or at least about or lower than about 0.0001 femtomolar.

[0124] In some embodiments, the template may be present in any nucleic acid sample of interest, including a nucleic acid sample isolated from a single cell, a plurality of cells (e.g., cultured cells), a tissue, an organ, or an organism (e.g., bacteria, yeast, or the like). In some embodiments, the nucleic acid sample is isolated from a cell(s), tissue, organ, and / or the like of a mammal (e.g., a human, a rodent (e.g., a mouse), or any other mammal of interest). In some embodiments, the nucleic acid sample is isolated from a source other than a mammal, such as bacteria, yeast, insects (e.g., drosophila), amphibians (e.g., frogs (e.g., Xenopus)), viruses, plants, or any other non-mammalian nucleic acid sample source.

[0125] In some embodiments, the template is optimized. In some embodiments, the acceptor template or acceptor nucleic acid molecule comprises at least one modified nucleotide. In some embodiments, the acceptor template or acceptor nucleic acid molecule is engineered to improve template jumping and / or conversion efficiency. In some embodiments, the acceptor template or acceptor nucleic acid molecule is optimized at the 3'-end. In some embodiments, the optimization prevents secondary structure formation and / or nucleotide composition.

[0126] In some embodiments, the methods described herein may further comprise optimization of the template (e.g. donor template). In some embodiments, optimization of the template comprises contacting the template (e.g. RNA) with an agent capable of removing the 5' cap structure of fthe template (e.g., mRNA). In some embodiments, the removal of the cap structure is performed under conditions permitting the removal of the cap structure by the agent. In some embodiments, the methods described herein further include dephosphorylation of for example, the decapped template. In some embodiments, the method further includes adding a dephosphorylating agent to the decapped template under conditions permitting dephosphorylation.

[0127] In some embodiments, any method described herein may further comprise optimization of the template. In some embodiments, optimization of the template comprises: contacting a sample comprising a template with an agent that removes a 5' cap structure of the template, under conditions permitting the removal of the cap structure by the agent. In some embodiments, the optimization of the template may further comprise adding a dephosphorylating agent under conditions permitting the dephosphorylation of the decapped template by the agent. In some embodiments, the template (e.g. RNA molecule) is dephosphorylated after synthesis or isolation. In some embodiments, the dephosphorylation is achieved by treatment of the nucleic acid (e.g., RNA) molecule with alkaline phosphatase. In some embodiments, the isolated donor template, such as RNA or mRNA, is decapped and dephosphorylated after isolation. Methods of decapping nucleic acids (e.g., RNAs) include both enzymatic methods (such as by using a pyrophosphatase such as tobacco pyrophosphatase) and chemical methods (such as periodate oxidation and beta elimination). Methods for dephosphorylation of nucleic acid (e.g., RNA) may use alkaline phosphatase. In some embodiments, the isolated mRNA is decapped (using tobacco acid pyrophosphatase, for example) and dephosphorylated (e.g., by using alkaline phosphatase). In some embodiments, the removal of the RNA cap structure is by either enzymatic treatment of the mRNA with a pyrophosphatase or chemical decapping (e.g., by periodate oxidation and beta elimination). In some embodiments, the mRNA is modified with a tag.

[0128] In some embodiments, any of the methods described herein is carried out in one-pot (e.g., single vessel). In some embodiments, the reactions are carried out in a one-pot (e.g., single vessel). In some embodiments, the reaction is a one-pot (e.g., single vessel) reaction.

[0129] In some embodiments, template jumping is dependent on the concentration of the acceptor nucleic acid molecule.

[0130] In some embodiments, the modified enzyme (e.g., modified reverse transcriptase), modified reverse transcriptase, non-naturally occurring enzyme, modified polypeptide having reverse transcriptase activity comprises at least one modification relative to the wild type, unmodified counterpart, or naturally occurring enzyme. In some embodiments, the modified non-LTR retrotransposon comprises at least one modification of a wild-type or unmodified non-LTR retrotransposon. In some embodiments, the modified R2 reverse transcriptase comprises at least one modification of a wild-type or unmodified R2 reverse transcriptase. In some embodiments, the modified reverse transcriptase comprises at least one modification of a wild-type or unmodified reverse transcriptase. In some embodiments, the modified polypeptide having reverse transcriptase activity comprises at least one modification of a wild-type or unmodified polypeptide having reverse transcriptase activity. In some embodiments, the modification comprises at least one truncation (e.g., N-terminal truncation, C-terminal truncation, and / or N- and C-terminal truncations). In some embodiments, the modification comprise(s) site-specific incorporation, and / or addition, and / or deletion, and / or substitution of amino acid(s) at positions of interest. In some embodiments, the modification enhances the biological properties of the modified enzyme or modified polypeptide relative to the wild-type or unmodified enzyme or polypeptide. In some embodiments, the modification improves at least one enzyme property of the modified enzyme or polypeptide relative to the wild-type or unmodified enzyme or polypeptide. In some embodiments, the modification(s) serve as a point of attachment for, e.g., labels and protein half-life extension agents, and for purposes of affixing the variants to the surface of a solid support. In some embodiments, the methods described herein are methods of producing cells capable of producing the modified enzymes (e.g., modified reverse transcriptase) or modified polypeptides, and of producing vectors containing DNA or RNA encoding the modified enzymes (e.g., modified reverse transcriptase) or modified polypeptides. In some embodiments, the truncation is based on a two-step process. In some embodiments, the first step for selecting a truncation includes analyzing the domains and motifs structure(s) and function(s) of a class of enzymes, or proteins, or polypeptides. In some embodiments, the enzymes, or proteins, or polypeptides are non-LTR retrotransposons, reverse transcriptases, R2 reverse transcriptase, LTR retrotransposons, R2 non-LTR retrotransposons, or any combination thereof. In some embodiments, the enzymes, or proteins, or polypeptides are from different organisms. In some embodiments, all the domains of the enzymes, or proteins, or polypeptides are present. In some embodiments, all the domains are present to ensure reverse transcriptase activity. In some embodiments, all the domains are present to ensure the unique properties essential for the methods described herein. In some embodiments, the domains responsible for reverse transcriptase activity are not modified. In some embodiments, the R2 domain does not comprise modifications. In some embodiments, the R2 domain may comprise modifications. In some embodiments, the truncated variants show expression level. In some embodiments, the truncated variants that show promising expression level are further subject to small adjustment(s) in the sequence (step two). In some embodiments, the small adjustment(s) in the sequence include deletion, insertion, and / or substitution of amino acid(s). In some embodiments, the deletion, insertion, and / or substitution of amino acid(s) may include one or several amino acid(s). In some embodiments, the deletion, insertion, and / or substitution of amino acid(s) further optimize expression and / or stability (e.g., thermostability).

[0131] In some embodiments, the modified enzyme (e.g., modified reverse transcriptase), modified reverse transcriptase, or modified polypeptides has an N-terminal truncation, a C-terminal truncation, or both, relative to the wild type or unmodified enzyme (e.g., wild-type reverse transcriptase) or wild-type or unmodified polypeptide. In some embodiments, the polymerase comprises an N-terminal truncation, a C-terminal truncation, or both. In some embodiments, the modified reverse transcriptase comprises N-terminal truncation, C-terminal truncation, or a combination of N-terminal and C-terminal truncation(s). In some embodiments, the modified enzyme comprises N-terminal truncation, C-terminal truncation, or a combination of N-terminal and C-terminal truncation(s). In some embodiments, the modified polypeptide comprises N-terminal truncation, C-terminal truncation, or a combination of N-terminal and C-terminal truncation(s). In some embodiments, the truncation comprises the sequence MAHHHHHHVGTVGTGGGSGGASTAL. In some embodiments, the modified reverse transcriptase, modified enzyme, modified polypeptide, modified non-LTR retrotransposon, or modified R2 reverse transcriptase comprises a truncation of less than about 100 amino acid residues. In some embodiments, the modified reverse transcriptase, modified enzyme, modified polypeptide, modified non-LTR retrotransposon, or modified R2 reverse transcriptase comprises at least one of: (a) an amino-terminal truncation of less than about 400 amino acid residues and (b) a carboxyl-terminal truncation of less than about 400 amino acid residues. In some embodiments, the modified reverse transcriptase, modified enzyme, modified polypeptide, modified non-LTR retrotransposon, or modified R2 reverse transcriptase lacks up to: about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 11, about 12, about 13, about 14, about 15, about 16, about 17, about 18, about 19, about 20, about 21, about 22, about 23, about 24, about 25, about 30, about 50, about 75, about 100, about 120, about 150, about 175, about 200, about 220, about 250, about 275, about 280, about 290, about 300, about 325, about 350, about 375, about 380, about 390, about 400, or about 450 amino acids from the N-terminus, C-terminus, or both. In some embodiments, the modified reverse transcriptase, modified enzyme, modified polypeptide, modified non-LTR retrotransposon, or modified R2 reverse transcriptase may alternately or additionally have one or more internal deletions of up to: about 1, about 2, about 3, about 4, about 5, about 6, about 7, about 8, about 9, about 10, about 11, about 12, about 13, about 14, about 15, about 16, about 17, about 18, about 19, about 20, about 21, about 22, about 23, about 24, or about 25 amino acids, about 30, about 50, about 75, about 100, about 120, about 150, about 175, about 200, about 220, about 250, about 275, about 280, about 290, about 300, about 325, about 350, about 375, about 380, about 390, or a total of about 450 amino acids. In some embodiments, the N-terminal truncation, C-terminal truncation, or both, may comprise deletions from about 1 to about 50 amino acids, from about 1 to about 25, from about 1 to about 70, from about 10 to about 50, from about 20 to about 30, from about 15 to about 100, from about 1 to about 150, from about 15 to about 60, from about 15 to about 40, from about 1 to about 10, from about 10 to 35, from about 50 to about 100, from about 20 to about 150, from about 200 to about 350, from about 25 to about 350, from about 150 to about 400, from about 50 to about 400, from about 50 to about 450, from about 200 to about 400, or from about 50 to about 350, or from about 50 to about 400 amino acids. In some embodiments, the N-terminal truncation removes at least about 5, at least about 10, at least about 15, at least about 20, at least about 25, at least about 30, at least about 35, at least about 40, at least about 50, at least about 60, at least about 65, at least about 70, at least about 75, at least about 80, at least about 90, at least about 95, at least about 100, at least about 120, at least about 130, at least about 140, at least about 150, at least about 175, at least about 200, at least about 220, at least about 250, at least about 275, at least about 300, at least about 325, at least about 350, at least about 375, or at least about 400 amino acids. In some embodiments, the C-terminal truncation removes at least about 5, at least about 10, at least about 15, at least about 20, at least about 25, at least about 30, at least about 35, at least about 40, at least about 50, at least about 60, at least about 65, at least about 70, at least about 75, at least about 80, at least about 90, at least about 95, at least about 100, at least about 120, at least about 130, at least about 140, at least about 150, at least about 175, at least about 200, at least about 220, at least about 250, at least about 275, at least about 300, at least about 325, at least about 350, at least about 375, or at least about 400 amino acids. In some embodiments, the N-terminal truncation lacks about 5, about 10, about 15, about 20, about 25, about 30, about 35, about 40, about 50, about 60, about 65, about 70, about 75, about 80, about 90, about 95, about 100, about 120, about 130, about 140, about 150, about 175, about 200, about 220, about 250, about 275, about 300, about 325, about 350, about 375, or about 400 amino acids. In some embodiments, the C-terminal truncation lacks about 5, about 10, about 15, about 20, about 25, about 30, about 35, about 40, about 50, about 60, about 65, about 70, about 75, about 80, about 90, about 95, about 100, about 120, about 130, about 140, about 150, about 175, about 200, about 220, about 250, about 275, about 300, about 325, about 350, about 375, or about 400 amino acids. In some embodiments, the N-terminal truncation lacks no more than about 5, no more than about 10, no more than about 15, no more than about 20, no more than about 25, no more than about 30, no more than about 35, no more than about 40, no more than about 50, no more than about 60, no more than about 65, no more than about 70, no more than about 75, no more than about 80, no more than about 90, no more than about 95, no more than about 100, no more than about 120, no more than about 130, no more than about 140, no more than about 150, no more than about 175, no more than about 200, no more than about 220, no more than about 250, no more than about 275, no more than about 300, no more than about 325, no more than about 350, no more than about 375, or no more than about 400 amino acids. In some embodiments, the C-terminal truncation lacks no more than about 5, no more than about 10, no more than about 15, no more than about 20, no more than about 25, no more than about 30, no more than about 35, no more than about 40, no more than about 50, no more than about 60, no more than about 65, no more than about 70, no more than about 75, no more than about 80, no more than about 90, no more than about 95, no more than about 100, no more than about 120, no more than about 130, no more than about 140, no more than about 150, no more than about 175, no more than about 200, no more than about 220, no more than about 250, no more than about 275, no more than about 300, no more than about 325, no more than about 350, no more than about 375, or no more than about 400 amino acids. In some embodiments, the truncation comprises an N-terminal truncation that removes at least about, at most about, or about 5, 10, 15, 20, 25, 30, 40, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375, 400, 425, 450, 475, or 500 amino acids. In some embodiments, the truncation comprises a C-terminal truncation that removes at least about, at most about, or about 5, 10, 15, 20, 25, 30, 40, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300, 325, 350, 375, 400, 425, 450, 475, or 500 amino acids. In some embodiments, the N-terminal truncation, the C-terminal truncation, or both, may be more than about 500 amino acids, more than about 1000 amino acids, more than about 1500 amino acids, more than about 2000 amino acids, more than about 5000 amino acids, more than about 10000 amino acids, more than about 100000 amino acids, more than about 1000000 amino acids.

[0132] In some embodiments, truncations of regions which do affect functional activity of a protein or enzyme may be engineered. In some embodiments, truncations of regions which do not affect functional activity of a protein or enzyme may be engineered. A truncation may comprise a truncation of less than about 5, less than about 10, less than about 15, less than about 20, less than about 25, less than about 30, less than about 35, less than about 40, less than about 45, less than about 50, less than about 60, less than about 70, less than about 80, less than about 90, less than about 100, less than about 125, less than about 150, less than about 200, less than about 250, less than about 300, less than about 350, less than about 400 or more amino acids. A truncation may comprise a truncation of more than about 5, more than about 10, more than about 15, more than about 20, more than about 25, more than about 30, more than about 35, more than about 40, more than about 45, more than about 50, more than about 60, more than about 70, more than about 80, more than about 90, more than about 100, more than about 125, more than about 150, more than about 200, more than about 250, more than about 300, more than about 350, more than about 400 or more amino acids. A truncation may comprise a truncation of about 5%, about 10%, about 15%, about 20%, about 25%, about 30%, about 35%, about 40%, about 45%, about 50%, about 55%, about 60%, about 65%, about 70%, about 75%, about 80%, about 85%, about 87%, about 90%, about 92%, about 95% or about 100% of the polypeptide or enzyme.

[0133] In some embodiments, the variant or modified enzyme or modified protein may comprise one or more modification(s) at an amino acid position. In some embodiments, a variant, a mutant, or modified polypeptides or enzymes as described herein may possess an increased activity, such as an increased RNA-dependent DNA polymerase activity or a DNA-dependent DNA polymerase activity, compared to the corresponding unmutated or unmodified or wildtype polymerase or as compared to one or more polymerases (e.g., RNA-dependent DNA polymerase, or a reverse transcriptase). In some embodiments, a polymerase or a reverse transcriptase having an increase in activity may be a modified polymerase or a modified reverse transcriptase that has at least about a 5% increase, at least about a 10% increase, at least about a 25% increase, at least about a 30% increase, at least about a 50% increase, at least about a 100% increase, at least about a 150% increase, at least about a 200% increase, at least about a 300% increase, at least about a 500% increase, at least about a 1,000% increase, at least about a 2,500% increase or at least about a 5,000% increase as compared to (1) the corresponding unmutated or wild-type enzyme; or (2) a particular polymerase (e.g., RNA-dependent DNA polymerase, reverse transcriptase) or a particular reverse transcriptase, or a group of polymerases, or a group of reverse transcriptases. In some embodiments, the modified polymerase or the modified reverse transcriptase as described herein may have an increase in activity of from about 5% to about 5,000%, from about 5% to about 2,500%, from about 5% to about 1000%, from about 5% to about 500%, from about 5% to about 250%, from about 5% to about 100%, from about 5% to about 50%, from about 5% to about 25%, from about 25% to about 5,000%, from about 25% to about 2,500%, from about 25% to about 1,000%, from about 25% to about 500%, from about 25% to about 250%, from about 25% to about 100%, from about 100% to about 5,000%, from about 100% to about 2,500%, from about 100% to about 1000%, from about 100% to about 500%, or from about 100% to about 250%. An increase in RNA-dependent DNA polymerase activity and / or DNA-dependent DNA polymerase for a modified polymerase or modified reverse transcriptase as described herein may also be measured according to relative activity compared to (1) the corresponding unmodified or wild-type enzyme; or (2) a particular polymerase (e.g., RNA-dependent DNA polymerase, reverse transcriptase) or a particular reverse transcriptase, or a group of polymerases, or a group of reverse transcriptases. In some embodiments, the increase in such relative activity is at least about 1.1, 1.2, 1.5, 2, 5, 10, 25, 50, 75, 100, 150, 200, 300, 500, 1,000, 2,500, 5,000, 10,000, or 25,000 fold when the activity of a modified polymerase or modified reverse transcriptase as described herein is compared to (1) the corresponding unmutated or wild-type enzyme; or (2) a particular polymerase (e.g., RNA-dependent DNA polymerase, reverse transcriptase) or a particular reverse transcriptase, or a group of polymerases, or a group of reverse transcriptases. Thus a modified polymerase or modified reverse transcriptase as described herein may have an increased RNA-dependent DNA polymerase and / or an increased DNA-dependent DNA polymerase activity of from about 1.1 fold to about 25,000 fold, from about 1.1 fold to about 10,000 fold, from about 1.1 fold to about 5,000 fold, from about 1.1 fold to about 2,500 fold, from about 1.1 fold to about 1,000 fold, from about 1.1 fold to about 500 fold, from about 1.1 fold to about 250 fold, from about 1.1 fold to about 50 fold, from about 1.1 fold to about 25 fold, from about 1.1 fold to about 10 fold, from about 1.1 fold to about 5 fold, from about 5 fold to about 25,000 fold, from about 5 fold to about 5,000 fold, from about 5 fold to about 1,000 fold, from about 5 fold to about 500 fold, from about 5 fold to about 100 fold, from about 5 fold to about 50 fold, from about 5 fold to about 25 fold, from about 50 fold to about 25,000 fold, from about 50 fold to about 5,000 fold, from about 50 fold to about 1,000 fold, from about 50 fold to about 500 fold, from about 50 fold to about 100 fold, from about 100 fold to about 25,000 fold, from about 1,000 fold to about 25,000 fold, from about 4,000 fold to about 25,000 fold, from about 10,000 fold to about 25,000 fold, from about 15,000 fold to about 25,000 fold, from about 1,000 fold to about 10,000 fold, from about 2,500 fold, to about 10,000 fold, from about 5,000 fold to about 10,000 fold, from about 7,500 fold to about 10,000 fold, from about 1,000 fold to about 15,000 fold, from about 2,500 fold, to about 15,000 fold, from about 5,000 fold to about 15,000 fold, from about 7,500 fold to about 15,000 fold, from about 10,000 fold to about 15,000 fold, or from about 12,500 fold to about 15,000 fold.

[0134] Described herein is a modified enzyme, modified polypeptide having reverse transcriptase activity, or a non-naturally occurring enzyme exhibits an altered (e.g., increased or decreased) processivity for a given nucleotide substrate relative to an unmodified or naturally occurring counterpart. In some embodiments, the modified enzyme, modified polypeptide having reverse transcriptase activity, or a non-naturally occurring enzyme exhibits a processivity for a given nucleotide substrate that is at least about 5%, 10%, 25%, 37.5%, 50%, 75%, 100%, 110%, 125%, 150%, 200%, 250%, 500%, 750%, 1,000%, 5,000% or 10,000% as high as the processivity of a reference enzyme for the same nucleotide substrate. In some embodiments, the reference enzyme is the unmodified counterpart of the modified enzyme. In some embodiments, the reference enzyme is a reverse transcriptase. In some embodiments, the reference enzyme is a non-LTR retrotransposon. In some embodiments, the reference enzyme is a LTR retrotransposon. In some embodiments, the reference enzyme is an R2 reverse transcriptase. In some embodiments, the reference enzyme or polypeptide comprises an amino acid sequence of SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 9, SEQ ID NO: 10, SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 26, SEQ ID NO: 27, SEQ ID NO: 28, SEQ ID NO: 29, SEQ ID NO: 30, SEQ ID NO: 31, SEQ ID NO: 32, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, SEQ ID NO: 36, SEQ ID NO: 37, SEQ ID NO: 38, SEQ ID NO: 39, SEQ ID NO: 40, SEQ ID NO: 41, SEQ ID NO: 42, SEQ ID NO: 43, SEQ ID NO: 44, SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO: 47, and / or SEQ ID NO: 48. In some embodiments, an R2 comprises at least one mutation and / or modification. In some embodiments, an R2 comprises an amino acid sequence of SEQ ID NO: 49, SEQ ID NO: 50, SEQ ID NO: 51, SEQ ID NO: 52, SEQ ID NO: 53, SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56, SEQ ID NO: 57, SEQ ID NO: 58, SEQ ID NO: 59, SEQ ID NO: 60, SEQ ID NO: 61, SEQ ID NO: 62, SEQ ID NO: 63, SEQ ID NO: 64, SEQ ID NO: 65, SEQ ID NO: 66, or SEQ ID NO: 67. In some embodiments, an R2 and / or a modified enzyme and / or a modified reverse transcriptase comprises a mutation at one or more amino acids selected from C952S, and / or C956S, and / or C952S, C956S (double mutant), and / or C969S, and / or H970Y, and / or R979Q, and / or R976Q, and / or R1071S, and / or R328A, and / or R329A, and / or Q336A, and / or R328A, R329A, Q336A (triple mutant), and / or G426A, and / or D428A, and / or G426A, D428A (double mutant), and / or any combination thereof. In some embodiments, the amino acid position is based on SEQ ID NO: 52. In some embodiments, the amino acid position is based on a wild-type reverse transcriptase. In some embodiments, the amino acid position is based on a wild-type R2. In some embodiments, a cysteine is mutated. In some embodiments, a cysteine is mutated to a serine. In some embodiments, an arginine is mutated. In some embodiments, an arginine is mutated to a serine, or a glutamine, or an alanine. In some embodiments, an amino acid is mutated to an alanine. In some embodiments, a glutamine is mutated to an alanine. In some embodiments, an aspartic acid is mutated to an alanine. In some embodiments, a glycine is mutated to an alanine. In some embodiments, a histidine is mutated to a tyrosine.

[0135] In some embodiments, a variant, or a modified enzyme (e.g., modified reverse transcriptase), or a modified polypeptide having reverse transcriptase activity as described herein comprises at least one altered characteristic that improves enzyme property. In some embodiments, a variant or a modified enzyme (e.g., modified reverse transcriptase) or a modified polypeptide having reverse transcriptase activity as described herein comprises at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 81%, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, and at least about 99% sequence identity to an amino acid sequence as described herein. In some embodiments, a variant, or a modified enzyme, or a modified polypeptide having reverse transcriptase activity comprises at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 81%, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, and / or at least about 99% sequence identity to an amino acid sequence corresponding to a GenBank number in TABLE 1. In some embodiments, a variant, or a modified enzyme, or a modified polypeptide having reverse transcriptase activity comprises at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 81%, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, and / or at least about 99%, sequence identity to an amino acid sequence set forth in SEQ ID NO: 1, SEQ ID NO: 2, SEQ ID NO: 3, SEQ ID NO: 4, SEQ ID NO: 5, SEQ ID NO: 6, SEQ ID NO: 7, SEQ ID NO: 8, SEQ ID NO: 9, SEQ ID NO: 10, SEQ ID NO: 11, SEQ ID NO: 12, SEQ ID NO: 13, SEQ ID NO: 14, SEQ ID NO: 15, SEQ ID NO: 16, SEQ ID NO: 17, SEQ ID NO: 18, SEQ ID NO: 19, SEQ ID NO: 20, SEQ ID NO: 21, SEQ ID NO: 22, SEQ ID NO: 23, SEQ ID NO: 24, SEQ ID NO: 25, SEQ ID NO: 26, SEQ ID NO: 27, SEQ ID NO: 28, SEQ ID NO: 29, SEQ ID NO: 30, SEQ ID NO: 31, SEQ ID NO: 32, SEQ ID NO: 33, SEQ ID NO: 34, SEQ ID NO: 35, SEQ ID NO: 36, SEQ ID NO: 37, SEQ ID NO: 38, SEQ ID NO: 39, SEQ ID NO: 40, SEQ ID NO: 41, SEQ ID NO: 42, SEQ ID NO: 43, SEQ ID NO: 44, SEQ ID NO: 45, SEQ ID NO: 46, SEQ ID NO: 47, and / or SEQ ID NO: 48. In some embodiments, a variant, or a modified enzyme, or a modified polypeptide having reverse transcriptase activity comprises at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 81%, at least about 82%, at least about 83%, at least about 84%, at least about 85%, at least about 86%, at least about 87%, at least about 88%, at least about 89%, at least about 90%, at least about 91%, at least about 92%, at least about 93%, at least about 94%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, and / or at least about 99% sequence identity to an amino acid sequence set forth in SEQ ID NO: 49, SEQ ID NO: 50, SEQ ID NO: 51, SEQ ID NO: 52, SEQ ID NO: 53, SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56, SEQ ID NO: 57, SEQ ID NO: 58, SEQ ID NO: 59, SEQ ID NO: 60, SEQ ID NO: 61, SEQ ID NO: 62, SEQ ID NO: 63, SEQ ID NO: 64, SEQ ID NO: 65, SEQ ID NO: 66, and / or SEQ ID NO: 67 (see TABLE 2). SEQ ID NO: 49 is an example of an R2 RT C-truncation, SEQ ID NO: 50 is an example of an R2 RT N-truncation, SEQ ID NO: 51 is an example of an R2 RT N- and C-truncation, SEQ ID NO: 52 is an example of an R2 wild type. SEQ ID NO: 53-67 are examples of R2 with single, double, or triple mutations (TABLE 2). In some embodiments, the modified reverse transcriptase is derived from an arthropod. In , the modified reverse transcriptase is derived from the arthropod Bombyx mori. TABLE 1GenBankDescriptionGI numberSEQ ID NO:AAB59214.1reverse transcriptase-like protein [Bombyx mori]9036951T18197reverse transcriptase-like protein - silkworm75117842KMQ90176.1reverse transcriptase [Lasius niger]8616308693KYB24671.1Retrovirus-related Pol polyprotein from type-2 retrotransposable element R2DM-like Protein [Tribolium castaneum]10043945264KMQ90064.1reverse transcriptase [Lasius niger]8616304805ACJ71597.1reverse transcriptase [Rhynchosciara americana]2159820906AFM44926.1R2 protein [Eyprepocnemis plorans]3918621737AHN53448.1reverse transcriptase [Nuttalliella namaqua]5991274918ACJ46647.1reverse transcriptase [Triops cancriformis]2133997439BAC82590.1reverse transcriptase [Ciona intestinalis]3439252510AAB94032.1reverse transcriptase domain protein [Drosophila mercatorum]273595711AAC34906.1reverse transcriptase [Forficula auricularia]355977612BAC82589.1reverse transcriptase [Ciona intestinalis]3439252313AIL01110.1reverse transcriptase [Bacillus rossius]67427509114AF019998.1R2 protein [Lepidurus couesii]39717483415KMQ88340.1reverse transcriptase [Lasius niger]86162470416AF019997.1R2 protein [Lepidurus couesii]39717483217AAC34903.1reverse transcriptase [Anurida maritima]355977018AF019995.1R2 protein [Lepidurus apus lubbocki]39717482819BAC82591.1reverse transcriptase [Ciona intestinalis]3439252720CAX83712.1endonuclease-reverse transcriptase [Schistosoma japonicum]25458731021XP_009165216.1hypothetical protein T265_13057 [Opisthorchis viverrini]68437589322AAB94040.1reverse transcriptase [Hippodamia convergens]273605023AAV85443.1reverse transcriptase-like protein [Amblyomma americanum]5626794124AAV85445.1reverse transcriptase-like protein [Ixodes scapularis]5626794525KRY44798.1Retrovirus-related Pol polyprotein from type-2 retrotransposable element R2DM [Trichinella britovi]95438071726AAV85444.1reverse transcriptase-like protein5626794327[Rhipicephalus microplus]KRX52183.1Retrovirus-related Pol polyprotein from type-2 retrotransposable element R2DM [Trichinella sp. T9]95425852428KRX72028.1Retrovirus-related Pol polyprotein from type-2 retrotransposable element R2DM [Trichinella sp. T6]95428059729AFO19999.1R2 protein [Lepidurus couesii]39717483630AAA21258.1reverse transcriptase [Drosophila ambigua]53313531KRX12851.1Retrovirus-related Pol polyprotein from type-2 retrotransposable element R2DM [Trichinella nelsoni]95420291832KFD59471.1hypothetical protein M514_11684 [Trichuns suis]66931886933KXZ75771.1hypothetical protein TcasGA2_TC031700 [Tribolium castaneum]100417303134XP_002412745.1reverse transcriptase, putative [Ixodes scapularis]24168376435BAE46603.1reverse transcriptase [Eptatretus burgeri]7779948736AFO20000.1R2 protein [Triops cancriformis]39717483837KRX36111.1Retrovirus-related Pol polyprotein from type-2 retrotransposable element R2DM [Trichinella murrelli]95424033838KRZ66264.1Retrovirus-related Pol polyprotein from type-2 retrotransposable element R2DM [Trichinella papuae]95458856739KRY45664.1Retrovirus-related Pol polyprotein from type-2 retrotransposable element R2DM [Trichinella britovi]95438201440CAJ00246.1TPA: polyprotein [Schistosoma mansoni]6762571741Q03278Retrovirus-related Pol polyprotein from type-1retrotransposable element R2 [Nasonia vitripennis (Parasitic wasp)]285155042Q03279Retrovirus-related Pol polyprotein from type-1 retrotransposable element R2 [Bradysia coprophila (Dark-winged fungus gnat) (Sciara coprophila)]54854643KXZ75830.1hypothetical protein TcasGA2_TC031908 [Tribolium castaneum]100417328944P16423.1RecName: Full=Retrovirus-related Pol polyprotein from type-2 retrotransposable element R2DM [Drosophila melanogaster]13055145KRX34481.1Retrovirus-related Pol polyprotein from type-2 retrotransposable element R2DM [Trichinella murrelli]95423816546EEB15300.1[Pediculus humanus corporis] - reverse transcriptase, putative21251255747XP_002431867.1reverse transcriptase, putative [Pediculus humanus corporis]48 TABLE 2 DescriptionSequenceSEQ ID NO:Example of a C-terminal truncation49Example of N-terminal truncation50Example of N-, C-truncation 51R2 wild type52C952S 53C956S54C952S,C956S 55C969S56H970Y 57R979Q58R976Q 59R1071S60R328A 61R329A62Q336A 63R328A,R329A,Q 336A64G426A 65D428A66G426A,D428A 67

[0136] In some embodiments, the polypeptides, proteins, enzymes, modified enzymes (e.g., modified reverse transcriptase), modified polypeptides, non-naturally occurring enzymes, or variants described herein comprise a fusion with a protein, a domain, a fusion partner, a carrier protein, a target sequence, an antigenic determinant, or any combination thereof. In some embodiments, the reverse transcriptase or modified reverse transcriptase is fused to a protein, a domain, a fusion partner, a target sequence, an antigenic determinant, or any combination thereof. In some embodiments, the non-LTR retrotransposon or modified non-LTR retrotransposon is fused to a protein, a domain, a fusion partner, a target sequence, an antigenic determinant, or any combination thereof. In some embodiments, the modified LTR retrotransposon is fused to a protein, a domain, a fusion partner, a target sequence, an antigenic determinant, or any combination thereof. In some embodiments, the modified R2 non-LTR retrotransposon is fused to a protein, a domain, a fusion partner, a target sequence, an antigenic determinant, or any combination thereof. In some embodiments, the modified R2 reverse transcriptase is fused to a protein, a domain, a fusion partner, a target sequence, an antigenic determinant, or any combination thereof. In some embodiments, the modified reverse transcriptase is fused to a protein, a domain, a fusion partner, a target sequence, an antigenic determinant, or any combination thereof. In some embodiments, the variant is fused to a protein, a domain, a fusion partner, a target sequence, an antigenic determinant, or any combination thereof. In some embodiments, the polypeptide having reverse transcriptase activity is fused to a protein, a domain, a fusion partner, a target sequence, an antigenic determinant, or any combination thereof.

[0137] In some embodiments, the fused polypeptides, proteins, enzymes, modified enzymes (e.g., modified reverse transcriptase), modified polypeptides, non-naturally occurring enzymes, or variants thereof increase stability (e.g., increase thermostability), increase shelf life, increase active fraction(s), and / or improve purification compared to the wild-type counterpart, naturally occurring enzyme, or unfused polypeptides, proteins, enzymes, or variants thereof. In some embodiments, a modified reverse transcriptase comprises a fusion partner or a carrier protein. In some embodiments, the selection of the fusion protein, domain, fusion partner, target sequence, antigenic determinant, or any combination thereof is based on the mechanism causing reduced or increased stability (e.g., increased thermostability), reduced or increased shelf life, and / or reduced or increased expression level (Costa et al., "Fusion tags for protein solubility, purification and immunogenicity in Escherichia coli: the novel Fh8 system. Front Microbiol. 2014 Feb 19; 5:63). In some embodiments, the fusion tags enhance the solubility of their partner proteins. In some embodiments, the fusion proteins form micelle-like structures. In some embodiments, the micelle-like structures are misfolded or unfolded proteins that are sequestered and protected from the solvent and / or the soluble protein domains face outward. In some embodiments, the fusion partners attract chaperones. In some embodiments, the fusion tag drives its partner protein into a chaperone-mediated folding pathway. In some embodiments, the MBP and / or N-utilization substance (NusA) are two fusion tags that present this mechanism. In some embodiments, the fusion partners have an intrinsic chaperone-like activity. In some embodiments, the hydrophobic patches of the fusion tag interact with partially folded passenger proteins, preventing self-aggregation, and promoting proper folding. In some embodiments, the solubility enhancer partners may play a passive role in the folding of their target proteins, reducing the chances for protein aggregation. In some embodiments, the fusion partners net charges. In some embodiments, the highly acidic fusion partners inhibit protein aggregation. In some embodiments, the fusion is with, but it is not limited to, Fh8, MBP, NusA, Trx, SUMO, GST, SET, GB1, ZZ, HaloTag, SNUT, Skp, T7PK, EspA, Mocr, Ecotin, CaBP, ArsC, IF2-domain I, an expressivity tag, an expressivity tag that is part of IF2-domain I, RpoA, SlyD, Tsf, RpoS, PotD, Crr , msyB, yjgD, rpoD, His6, or any combination thereof. In some embodiments, the fusion enhances protein solubility and / or purification. In some embodiments, the Fh8 may act as an effective solubility enhancer partner and / or robust purification. In some embodiments, the Fh8 fusion tag has an amino acid sequence comprising MPSVQEVEKLLHVLDRNGDGKVSAEELKAFADDSKCPLDSNKIKAFIKEHDKNKDGKLDLKEL VSILSS. In some embodiments, the codon optimized sequence comprises ATGCCGTCTGTTCAGGAAGTTGAAAAACTGCTGCACGTTCTGGACCGTAACGGTGACGGTAA AGTTTCTGCGGAAGAACTGAAAGCGTTCGCGGACGACTCTAAATGCCCGCTGGACTCTAACA AAATCAAAGCGTTCATCAAAGAACACGACAAAAACAAAGACGGTAAACTGGACCTGAAAG AACTGGTTTCTATCCTGTCTTCTTAG. In some embodiments, an enzyme, or a modified enzyme (e.g., modified reverse transcriptase), or a protein (e.g., modified protein), or a polypeptide (e.g., modified polypeptide), or a variant, or a product, or a nucleic acid molecule, or a cDNA molecule, or a template, or an acceptor nucleic acid molecule, or a primer, or an RNA, or a DNA, or a fragment nucleic acid, or a degraded nucleic acid, as described herein may comprise one or more tag(s). In some embodiments, the fragmented or degraded RNA or DNA, or a variant thereof may comprise one or more tag(s). In some embodiments, the R2 reverse transcriptase, or a variant thereof, may comprise one or more tag(s). In some embodiments, the non-LTR retrotransposon protein or polypeptide having reverse transcriptase activity, or a variant thereof, may comprise one or more tag(s). In some embodiments, the cDNA molecule may comprise one or more tag(s). In some embodiments, the tag may be captured on a solid support, facilitating the isolation of the enzyme, or protein, or polypeptide, or a variant, or a product as described herein. In some embodiments, the tag may be biotin that can be recognized by avidin. The affinity tag may include multiple biotin residues for increased binding to multiple avidin molecules. In some embodiments, the tag may include a functional group such as an azido group or an acetylene group, which enables capture through copper(I) mediated click chemistry (see H. C. Kolb and K. B. Sharpless, Drug Discovery Today, 2003, 8(24), 1128-1137). In some embodiments, the tag may include an antigen that may be captured by an antibody bound on a solid support. In some embodiments, the tag may include, but is not limited to, His-tag, His6-tag, Calmodulin-tag, CBP, CYD (covalent yet dissociable NorpD peptide), Strep II, FLAG-tag, HA-tag, Myc-tag, S-tag, SBP-tag, Softag-1, Softag-3, V5-tag, Xpress-tag, Isopeptag, SpyTag, B, HPC (heavy chain of protein C) peptide tags, GST, MBP, biotin, biotin carboxyl carrier protein, glutathione-S-transferase-tag, green fluorescent protein-tag, maltose binding protein-tag, Nus-tag, Strep-tag, thioredoxin-tag, and combinations thereof. In some embodiments, the tagged molecule may be subjected to sequencing.

[0138] In some embodiments, a molecular barcode may be attached to any region of a molecule. For example, the molecular barcode may be attached to the 5' or 3' end of a polynucleotide (e.g., DNA, RNA). For example, the target-specific region of the molecular barcode comprises a sequence that is complementary to a sequence in the 5' region of the molecule. The target-specific region of the molecular barcode may also comprise a sequence that is complementary to a sequence in the 3' region of the molecule. In some instances, the molecular barcode is attached a region within a gene or gene product. For example, genomic DNA is fragmented and a sample tag or molecular identifier label is attached to the fragmented DNA. In other instances, an RNA molecule is alternatively spliced and the molecular barcode is attached to the alternatively spliced variants. In another example, the polynucleotide is digested and the molecular barcode is attached to the digested polynucleotide. In another example, the target-specific region of the molecular barcode comprises a sequence that is complementary to a sequence within the molecule.

[0139] In some embodiments the method described herein comprises introducing a biotin moiety or another affinity purification moiety to, for example, a nucleic acid molecule, such as DNA, RNA, or a combination of DNA and RNA. In some embodiments, the method further comprises immobilizing the affinity purification tagged nucleic acid molecule on a solid support. In some embodiments the solid support is a sepharose resin or magnetic beads having an affinity purification material, such as avidin, streptavidin, chitin, glutathione and the like, bound thereto.

[0140] In some embodiments, the enzyme, or protein, or polypeptide, or a variant, or a product as described herein may be bound to a solid support. In some embodiments, the fragmented or degraded nucleic acid (e.g., RNA or DNA), or a variant thereof may be bound to a solid support. In some embodiments, the R2 reverse transcriptase, or a variant thereof, may be bound to a solid support. In some embodiments, the non-LTR retrotransposon protein or polypeptide having reverse transcriptase activity, or a variant thereof, may be bound to a solid support. In some embodiments, the cDNA molecule may be bound to a solid support. In some embodiments, the solid support may be glass, plastic, porcelain, resin, sepharose, silica, or other material. In some embodiments, the solid support may be a plate that is substantially flat substrates, gel, microbeads, magnetic beads, membrane, or other suitable shape and size. In some embodiments, the microbeads may have diameter between 10 nm to several millimeters. In some embodiments, the solid support may be non-porous or porous with various density and size of pores. In some embodiments the DNA and / or RNA fragment may be captured on a solid support, unwanted DNA and / or RNA may be washed away. In some embodiments, the DNA and / or RNA fragment may be released from the solid support, for example, by using restriction enzyme.

[0141] In some embodiments, the solid support may comprise the target nucleic acid binding region, wherein the target nucleic acid binding region comprises a sequence selected from the group consisting of a gene-specific sequence, an oligo-dT sequence, a random multimer, and any combination thereof. In some embodiments, the solid support further comprises a target nucleic acid or complement thereof. In some embodiments, the solid support comprises a plurality of target nucleic acids or complements thereof comprising from about 0.01% to about 100% of transcripts of a transcriptome of an organism or complements thereof, or from about 0.01% to about 100% of genes of a genome of an organism or complements thereof. In some embodiments, the cellular labels of the plurality of oligonucleotides comprise a first random sequence connected to a second random sequence by a first label linking sequence; and the molecular labels of the plurality of oligonucleotides comprise random sequences. In some embodiments, the solid support is selected from the group consisting of a polydimethylsiloxane (PDMS) solid support, a polystyrene solid support, a glass solid support, a polypropylene solid support, an agarose solid support, a gelatin solid support, a magnetic solid support, a pluronic solid support, and any combination thereof. In some embodiments, the plurality of oligonucleotides comprise a linker comprising a linker functional group, and the solid support comprises a solid support functional group; wherein the solid support functional group and linker functional group connect to each other. In some embodiments, the linker functional group and the solid support functional group are individually selected from the group consisting of C6, biotin, streptavidin, primary amine(s), aldehyde(s), ketone(s), and any combination thereof. In some embodiments, molecular labels of the plurality of oligonucleotides comprise at least 15 nucleotides.

[0142] In some embodiments, fusion partners may be removed from their target protein by enzymatic cleavage, chemical cleavage, and / or by using an in vivo cleavage strategy. In some embodiments, proteases may be used for tag removal. In some embodiments, the protease may be an endoprotease, serine protease, factor Xa, enterokinase, alpha-thrombin, a viral protease, tobacco etch virus (TEV), the human rhinovirus 3C protease, SUMO protease, exoprotease, metallocarboxypeptidase, or aminopeptidase. In some embodiments, a fusion tag may be removed by two purification steps. In some embodiments, the initial affinity purification step includes (e.g., via a histidine tag located at the N-terminal of the fusion protein), the purified fusion protein mixed in solution with the endoprotease (e.g., a his-tagged protease) to cleave off the tag. The cleaved target protein may be recovered in the flow-through sample after a second affinity purification step, in which the cleaved fusion tag and the added protease are collected in the eluted sample.

[0143] In some embodiments, the modified enzyme, modified reverse trancriptase, non-naturally occurring enzyme, or modified polypeptide having reverse transcriptase activity as described hereinshows activity, is capable of template jumping, and / or generate a nucleic acid molecule (e.g., cDNA molecule) without thermal cycling. In some embodiments, the modified reverse trancriptase, modified enzyme, non-naturally occurring enzyme, or the modified polypeptide having reverse transcriptase activity described herein shows activity, is capable of template jumping, and / or generate a nucleic acid, cDNA molecule at a temperature ranging from about 25 °C to about 42 °C, from about 12 °C to about 42 °C, from about 8 °C to about 50 °C, from about 4 °C to about 60 °C, from about 27 °C to about 35 °C, from about 28 °C to about 33 °C, from about 29 °C to about 32 °C, from about 30 °C to about 37 °C, from about 26 °C to about 38 °C, from about 30 °C to about 37 °C, from about 25 °C to about 32 °C, from about 29 °C to about 31 °C, from about 27 °C to about 38 °C, from about 29 °C to about 38 °C. In some embodiments, the non-naturally occurring enzyme, modified reverse trancriptase, modified enzyme, or modified polypeptide having reverse transcriptase activity described herein shows activity, is capable of template jumping, and / or generate a nucleic acid molecule (e.g., cDNA molecule) at about 30 °C, or at about 35 °C, or at about 25 °C. In some embodiments, the modified enzyme, modified reverse trancriptase, non-naturally occurring enzyme, or modified polypeptide having reverse transcriptase activity described herein shows activity, is capable of template jumping, and / or generate a nucleic acid molecule (e.g., cDNA molecule) at a temperature equal to less than about 38 °C, equal to less than about 42 °C, equal to less than about 50 °C, equal to less than about 60 °C, equal to less than about 35 °C, equal to less than about 30 °C, equal to less than about 28 °C, equal to less than about 25 °C, equal to less than about 20 °C, equal to less than about 12 °C, equal to less than about 8 °C, or equal to less than about 4 °C. In some embodiments, the modified enzyme, modified reverse trancriptase, non-naturally occurring enzyme, or modified polypeptide having reverse transcriptase activity described herein shows activity, is capable of template jumping, and / or generate a nucleic acid molecule (e.g., cDNA molecule) at a temperature equal to less than about 36 °C. In some embodiments, the modified enzyme, modified reverse trancriptase, non-naturally occurring enzyme, or modified polypeptide having reverse transcriptase activity of the present disclosure shows activity, is capable of template jumping, and / or generate a nucleic acid molecule (e.g., cDNA molecule) at room temperature. In some embodiments, the modified enzyme, modified reverse trancriptase, non-naturally occurring enzyme, or modified polypeptide having reverse transcriptase activity described herein shows activity, is capable of template jumping, and / or generate a nucleic acid molecule (e.g., cDNA molecule) at a temperature of at about or of at most about 8 °C, at about or of at most about 12 °C, at about or of at most about 20 °C, at about or of at most about 25 °C, at about or of at most about 28 °C, at about or of at most about 30 °C, at about or of at most about 31 °C, at about or of at most about 32 °C, at about or of at most about 33 °C, at about or of at most about 34 °C, at about or of at most about 35 °C, at about or of at most about 36 °C at about or of at most about 39 °C, at about or of at most about 40 °C, at about or of at most about 41 °C, at about or of at most about 42 °C, at about or of at most about 50 °C, at about or of at most about 55 °C, at about or of at most about 60 °C. In some embodiments, the modified enzyme, modified reverse trancriptase, non-naturally occurring enzyme, or modified polypeptide having reverse transcriptase activity described herein shows activity, is capable of template jumping, and / or generate a nucleic acid molecule (e.g., cDNA molecule) at a temperature equal to or less than about any temperature between about 42 °C to about 80 °C, or between about 35 °C to about 80 °C, or between about 30 °C to about 50 °C, or between about 8 °C to about 50 °C, or between about 12 °C to about 42 °C.

[0144] In some embodiments, a modified enzyme, modified reverse trancriptase, modified polypeptide having reverse transcriptase activity, or a non-naturally occurring enzyme as described herein has at least one altered characteristic relative to an unmodified or naturally occurring enzyme. In some embodiments, the altered characteristic enables the modified enzyme, modified reverse trancriptase, non-naturally occurring enzyme, or modified polypeptide having reverse transcriptase activity to generate a nucleic acid molecule and / or a complementary deoxyribonucleic acid (cDNA) molecule from a template nucleic acid molecule without thermal cycling. In some embodiments, a modified enzyme, modified reverse trancriptase, modified polypeptide having reverse transcriptase activity, or a non-naturally occurring enzyme as described herein is capable of generating one or more copies of the nucleic acid molecule or cDNA molecule at an error rate of at most about 0.5%, of at most about 1%, of at most about 1.5%, of at most about 2%, of at most about 2.5%, of at most about 3%, of at most about 3.5%, of at most about 4%, of at most about 4.5%, of at most about 5%, of at most about 6%, of at most about 7%, of at most about 8%, of at most about 9%, of at most about 10%, of at most about 15%, of at most about 20%, of at most about 25%, of at most about 30%, of at most about 40%, of at most about 45%, of at most about 50%, of at most about 60%, of at most about 65%, of at most about 70%, of at most about 75%, or of at most about 80%. In some embodiments, the modified enzyme, modified reverse trancriptase, modified polypeptide having reverse transcriptase activity, or the non-naturally occurring enzyme as described herein is a variant of any one of the sequences described herein. In some embodiments, the modified enzyme, modified reverse trancriptase, modified polypeptide having reverse transcriptase activity, or the non-naturally occurring enzyme as described herein is a variant of any one of the sequences corresponding to accession numbers provided in TABLE 1. In some embodiments, the modified enzyme, modified reverse trancriptase, modified polypeptide having reverse transcriptase activity, or the non-naturally occurring enzyme as described herein is a variant of any one of the sequences provided in SEQ ID Nos: 1-67. In some embodiments, a modified enzyme, modified reverse trancriptase, modified polypeptide having reverse transcriptase activity, or a non-naturally occurring enzyme as described herein has at least one altered characteristic that improves enzyme property relative to an unmodified or a naturally occurring enzyme. In some embodiments, the at least one altered characteristic that improves enzyme property comprises at least one of increased / improved stability (e.g., increased / improved thermostability), increased / improved specific activity, increased / improved protein expression, increased / improved purification, increased / improved processivity, increased / improved strand displacement, increased / improved template jumping, and increased / improved fidelity.

[0145] Described herein is a non-naturally occurring enzyme that subjects a template nucleic acid molecule to reverse transcription to generate a complementary deoxyribonucleic acid (cDNA) product and amplification of the cDNA product at a processivity of at least about 80%, at least about 85%, at least about 87%, at least about 90%, at least about 92%, at least about 95%, at least about 96%, at least about 97%, at least about 98%, at least about 99%, or at least about 99.5% per base as measured at about 12 °C, about 15 °C, about 20 °C, about 25 °C, about 30 °C, about 32 °C, about 35 °C, about 40 °C.

[0146] In some embodiments, the non-naturally occurring enzyme has a performance index greater than about 1.0 for at least one enzyme property. In some embodiments, enzyme property is at least one of the group consisting of improved stability (e.g., improved thermostability), specific activity, protein expression, purification, processivity, strand displacement, template jumping, increased DNA / RNA affinity, and fidelity.

[0147] Described herein is a non-naturally occurring enzyme that subjects a template nucleic acid molecule to reverse transcription to generate a complementary deoxyribonucleic acid (cDNA) product, a nucleic acid product, and amplification of the cDNA product in a time period of about 3 h or less and / or at a performance index greater than about 1.0 for at least one enzyme property selected from the group consisting of improved stability (e.g., improved thermostability), specific activity, protein expression, purification, processivity, strand displacement, template jumping, increased DNA / RNA affinity, and fidelity. In some embodiments, the temperature is from about 25 °C to about 40 °C (e.g., about 28 °C, about 30 °C, about 32 °C, about 35 °C, or about 37 °C). In some embodiments, the temperature is from about 8 °C to about 50 °C (e.g., about 8 °C, about 20 °C, about 42 °C, about 45 °C, or about 50 °C).

[0148] Described herein is a non-naturally occurring enzyme that subjects a template nucleic acid molecule to reverse transcription to generate a complementary deoxyribonucleic acid (cDNA) product and amplification of the cDNA product in a time period of 3 h or less (e.g., 2.5 h or less, 2 h or less, 1.5 h or less, 1 h or less, or 30 min or less) and / or at a processivity for a given nucleotide substrate that is at least about 5%, at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 85%, at least about 88%, at least about 90%, at least about 95%, or at least about 98% higher than the processivity of a reference enzyme for the same nucleotide substrate.

[0149] Described herein is a non-naturally occurring enzyme that subjects a template nucleic acid molecule to reverse transcription to generate a nucleic acid product and amplification of the nucleic acid product in a time period of 3 h or less (e.g., 2.5 h or less, 2 h or less, 1.5 h or less, 1 h or less, or 30 min or less) and / or at a processivity for a given nucleotide substrate that is at least about 5%, at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80%, at least about 85%, at least about 88%, at least about 90%, at least about 95%, or at least about 98% higher than the processivity of a reference enzyme for the same nucleotide substrate.

[0150] Described herein is a method of amplifying a nucleic acid molecule, comprising subjecting the nucleic acid molecule to nucleic acid amplification using a modified reverse transcriptase. In some embodiments, the reverse transcriptase is capable of amplifying the nucleic acid molecule at processivity of at least about 80%, at least about 88%, at least about 90%, at least about 95%, or at least about 98% per base at about 4 °C, about 8 °C, about 12 °C, about 30 °C, about 28 °C, about 29 °C, about 32 °C, about 35 °C, about 37 °C, about 42 °C, about 50 °C, or higher than about 42 °C.

[0151] In some embodiments, the method described herein further comprises using the modified reverse transcriptase to subject a template nucleic acid molecule to reverse transcription to yield the nucleic acid molecule. In some embodiments, the nucleic acid molecule is a cell-free nucleic acid molecule. In some embodiments, the template nucleic acid molecule is a cell-free nucleic acid molecule.

[0152] In some embodiments, primer extension or elongation reactions are utilized to generate amplified product. Primer extension / elongation reactions may comprise a cycle of incubating a reaction mixture at a denaturation temperature for a denaturation duration and incubating a reaction mixture at an elongation temperature for an elongation duration.

[0153] Any type of nucleic acid amplification reaction may be used to amplify a target nucleic acid and generate an amplified product. Moreover, amplification of a nucleic acid may linear, exponential, or a combination thereof. Amplification may be emulsion based or may be non-emulsion based. Examples of nucleic acid amplification methods include reverse transcription, primer extension, polymerase chain reaction, ligase chain reaction, helicase-dependent amplification, asymmetric amplification, rolling circle amplification, and multiple displacement amplification (MDA). In some embodiments, the amplified product may be DNA. In cases where a target RNA is amplified, DNA can be obtained by reverse transcription of the RNA and subsequent amplification of the DNA can be used to generate an amplified DNA product. The amplified DNA product may be indicative of the presence of the target RNA in the biological sample. In cases where DNA is amplified, any DNA amplification may be employed. Examples of DNA amplification methods include polymerase chain reaction (PCR), variants of PCR (e.g., real-time PCR, allele-specific PCR, assembly PCR, asymmetric PCR, digital PCR, emulsion PCR, dial-out PCR, helicase-dependent PCR, nested PCR hot start PCR, inverse PCR, methylation-specific PCR, miniprimer PCR, multiplex PCR, nested PCR, overlap-extension PCR thermal asymmetric interlaced PCR, touchdown PCR), and ligase chain reaction (LCR). In some cases, DNA amplification is linear. In some cases, DNA amplification is exponential. In some cases, DNA amplification is achieved with nested PCR, which can improve sensitivity of detecting amplified DNA products.

[0154] Denaturation temperatures may vary depending upon, for example, the particular biological sample analyzed, the particular source of target nucleic acid (e.g., viral particle, bacteria) in the biological sample, the reagents used, and / or the desired reaction conditions. In some embodiments, a denaturation temperature may be from about 80 °C to about 110 °C. In some embodiments, a denaturation temperature may be from about 90 °C to about 100 °C. In some embodiments, a denaturation temperature may be from about 90 °C to about 97 °C. In some examples, a denaturation temperature may be from about 92 °C to about 95 °C. In still other examples, a denaturation temperature may be about 80°, 81 °C, 82 °C, 83 °C, 84 °C, 85 °C, 86 °C, 87 °C, 88 °C, 89 °C, 90 °C, 91 °C, 92 °C, 93 °C, 94 °C, 95 °C, 96 °C, 97 °C, 98 °C, 99 °C, or 100 °C.

[0155] Denaturation durations may vary depending upon, for example, the particular biological sample analyzed, the particular source of target nucleic acid (e.g., viral particle, bacteria) in the biological sample, the reagents used, and / or the desired reaction conditions. In particular, the denaturation duration may be less than or equal to about 300 s, 240 s, 180 s, 120 s, 90 s, 60 s, 55 s, 50 s, 45 s, 40 s, 35 s, 30 s, 25 s, 20 s, 15 s, 10 s, 5 s, 2 s, or 1 s. For example, a denaturation duration may be no more than about 180 s, 120 s, 90 s, 60 s, 55 s, 50 s, 45 s, 40 s, 35 s, 30 s, 25 s, 20 s, 15 s, 10 s, 5 s, 2 s, or 1 s.

[0156] Elongation or extension temperatures may vary depending upon, for example, the particular biological sample analyzed, the particular source of target nucleic acid (e.g., viral particle, bacteria) in the biological sample, the reagents used, and / or the desired reaction conditions. In some embodiments, an elongation temperature may be from about 30 °C to about 80 °C. In some embodiments, an elongation temperature may be from about 35 °C to about 72 °C. In some embodiments, an elongation temperature may be from about 45 °C to about 68 °C. In some embodiments, an elongation temperature may be from about 35 °C to about 65 °C. In some embodiments, an elongation temperature may be from about 40 °C to about 67 °C. In some embodiments, an elongation temperature may be from about 50 °C to about 68 °C. In some embodiments, an elongation temperature may be about 0 °C, 1 °C, 2 °C, 3 °C, 4 °C, 5 °C, 6 °C, 7 °C, 8 °C, 9 °C, 10 °C, 11 °C, 12 °C, 13 °C, 14 °C, 15 °C, 16 °C, 17 °C, 18 °C, 19 °C, 34 °C, 33 °C, 32 °C, 31 °C, 30 °C, 20 °C, 21 °C, 22 °C, 23 °C, 24 °C, 25 °C, 26 °C, 27 °C, 28 °C, 29 °C, 35 °C, 36 °C, 37 °C, 38 °C, 39 °C, 40 °C, 41 °C, 42 °C, 43 °C, 44 °C, 45 °C, 46 °C, 47 °C, 48 °C, 49 °C, 50 °C, 51 °C, 52 °C, 53 °C, 54 °C, 55 °C, 56 °C, 57 °C, 58 °C, 59 °C, 60 °C, 61 °C, 62 °C, 63 °C, 64 °C, 65 °C, 66 °C, 67 °C, 68 °C, 69 °C, 70 °C, 71 °C, 72 °C, 73 °C, 74 °C, 75 °C, 76 °C, 77 °C, 78 °C, 79 °C, or 80 °C.

[0157] Elongation durations may vary depending upon, for example, the particular biological sample analyzed, the particular source of target nucleic acid (e.g., viral particle, bacteria) in the biological sample, the reagents used, and / or the desired reaction conditions. In some embodiments, an elongation duration may be less than or equal to about 360 s, less than or equal to about 300 s, 240 s, 180 s, 120 s, 90 s, 60 s, 55 s, 50 s, 45 s, 40 s, 35 s, 30 s, 25 s, 20 s, 15 s, 10 s, 5 s, 2 s, or 1 s. In some embodiments, an elongation duration may be no more than about 120 s, 90 s, 80 s, 70 s, 65 s, 60 s, 55 s, 50 s, 45 s, 40 s, 35 s, 30 s, 25 s, 20 s, 15 s, 10 s, 5 s, 2 s, or 1 s.

[0158] In some embodiments, multiple cycles of a primer extension reaction can be conducted. Any suitable number of cycles may be conducted. In some embodiments, the number of cycles conducted may be less than about 100, 90, 80, 70, 60, 50, 40, 30, 20, 10, or 5 cycles. The number of cycles conducted may depend upon, for example, the number of cycles (e.g., cycle threshold value (Ct)) necessary to obtain a detectable amplified product (e.g., a detectable amount of amplified DNA product that is indicative of the presence of a target RNA in a biological sample). In some embodiments, the number of cycles necessary to obtain a detectable amplified product (e.g., a detectable amount of DNA product that is indicative of the presence of a target RNA in a biological sample) may be less than about or about 100 cycles, 75 cycles, 70 cycles, 65 cycles, 60 cycles, 55 cycles, 50 cycles, 40 cycles, 35 cycles, 30 cycles, 25 cycles, 20 cycles, 15 cycles, 10 cycles, 8 cycles, 7 cycles, 5 cycles, or 4 cycles. Moreover, in some embodiments, a detectable amount of an amplifiable product (e.g., a detectable amount of DNA product that is indicative of the presence of a target RNA in a biological sample) may be obtained at a cycle threshold value (Ct) of less than 100, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 9, 8, 7, 6, 5, 4, 3, 2, 1.

[0159] In some embodiments, an amplification step (e.g., primer amplification, template amplification, nucleic acid amplification) comprises a PCR step. In some embodiments, each PCR cycle may comprise a denaturing step, an annealing step, and an extension step. In some embodiments, each PCR cycle may comprise a denaturing step and an extension step. In some embodiments, the PCR comprises at least about or about or at most about1 cycle, at least about or about or at most about 4 cycles, at least about or about or at most about 5 cycles, at least about or about or at most about 10 cycles, at least about or about or at most about 15 cycles, at least about or about or at most about 20 cycles, at least about or about or at most about 25 cycles, at least about or about or at most about 30 cycles, at least about or about or at most about 35 cycles, at least about or about or at most about 40 cycles, at least about or about or at most about 45 cycles, at least about or about or at most about 50 cycles, at least about or about or at most about 55 cycles, at least about or about or at most about 60 cycles, at least about or about or at most about 65 cycles, at least about or about or at most about 70 cycles, at least about or about or at most about 75 cycles, at least about or about or at most about 80 cycles, at least about or about or at most about 90 cycles, at least about or about or at most about 95 cycles, at least about or about or at most about 100 cycles, at least about or about or at most about 110 cycles, at least about or about or at most about 120 cycles, at least about or about or at most about 130 cycles, at least about or about or at most about 140 cycles, at least about or about or at most about 150 cycles, at least about or about or at most about 160. In some embodiments, the PCR comprises from about 10 cycles to 40 cycles, from about 20 cycles to 40 cycles, from about 20 cycles to 38 cycles, from about 20 cycles to 35 cycles, from about 10 cycles to 35 cycles, from about 10 cycles to 30 cycles, from about 25 cycles to 30 cycles, from about 20 cycles to 30 cycles, from about 4 cycles to 8 cycles, or from about 28 cycles to 32 cycles. In some embodiments, the reaction is heated to 95 °C for 3 min before the PCR cycle begins. In some embodiments, each PCR cycle comprises 95 °C for 3 s and 62 °C for 20 s. In some embodiments, each PCR cycle comprises 95 °C for 3 s, 54 °C for 10 s, and 64 °C for 20 s. In some embodiments, each PCR cycle comprises 95 °C for 3 s and 64 °C for 20 s. In some embodiments, each PCR cycle comprises 95 °C for 3 s and 62 °C for 60 s. In some embodiments, each PCR cycle comprises 95 °C for 3 s, 54 °C for 10 s, and 64 °C for 10 s. In some embodiments, the PCR comprises 30 cycles. In some embodiments, the reaction is heated to 68 °C after the completion of the PCR cycles. In some embodiments, the reaction is heated to 68 °C from about 1 s to about 5 s, from about 1 s to about 5 min, from about 1 min to about 5 min after the completion of the PCR cycles. In some embodiments, the PCR methods described herein comprises an extension or elongation step that is at least about 5 s long, at least about 6 s long, at least about 7 s long, at least about 8 s long, at least about 9 s long, at least about 10 s long, at least about 11 s long, at least about 12 s long, at least about 13 s long, at least about 14 s long, at least about 15 s long, at least about 20 s long, at least about 30 s long, at least about 40 s long, at least about 50 s long, at least about 60 s long, at least about 90 s long, at least about 120 s long, at least about 150 s long, at least about 180 s long, at least about 210 s long, at least about 240 s long, at least about 270 s long, at least about 300 s long, at least about 330 s long, at least about 360 s long, at least about 390 s long, or more.

[0160] The time for which amplification yields a detectable amount of amplified product indicative of the presence of a target nucleic acid amplified can vary depending upon the biological sample from which the target nucleic acid was obtained, the particular nucleic acid amplification reactions to be conducted, and the particular number of cycles of amplification reaction desired. In some embodiments, amplification of a target nucleic acid may yield a detectable amount of amplified product indicative to the presence of the target nucleic acid at time period of 120 min or less; 90 min or less; 60 min or less; 50 min or less; 45 min or less; 40 min or less; 35 min or less; 30 min or less; 25 min or less; 20 min or less; 15 min or less; 10 min or less; or 5 min or less.

[0161] In some embodiments, a biological sample may be preheated prior to conducting a primer extension reaction. The temperature (e.g., a preheating temperature) at which and duration (e.g., a preheating duration) for which a biological sample is preheated may vary depending upon, for example, the particular biological sample being analyzed. In some examples, a biological sample may be preheated for no more than about 60 min, 50 min, 40 min, 30 min, 25 min, 20 min, 15 min, 10 min, 9 min, 8 min, 7 min, 6 min, 5 min, 4 min, 3 min, 2 min, 1 min, 45 s, 30 s, 20 s, 15 s, 10 s, or 5 s. In some examples, a biological sample may be preheated at a temperature from about 80 °C to about 110 °C. In some examples, a biological sample may be preheated at a temperature from about 90 °C to about 100 °C. In some examples, a biological sample may be preheated at a temperature from about 90 °C to about 97 °C. In some examples, a biological sample may be preheated at a temperature from about 92 °C to about 95 °C. In some embodiments, a biological sample may be preheated at a temperature of about 80°C, 81 °C, 82 °C, 83 °C, 84 °C, 85 °C, 86 °C, 87 °C, 88 °C, 89 °C, 90 °C, 91 °C, 92 °C, 93 °C, 94 °C, 95 °C, 96 °C, 97 °C, 98 °C, 99 °C, or 100 °C.

[0162] In some embodiments, reagents necessary for conducting nucleic acid amplification may also include a reporter agent that yields a detectable signal whose presence or absence is indicative of the presence of an amplified product. The intensity of the detectable signal may be proportional to the amount of amplified product. In some cases, where amplified product is generated of a different type of nucleic acid than the target nucleic acid initially amplified, the intensity of the detectable signal may be proportional to the amount of target nucleic acid initially amplified. For example, in the case of amplifying a target RNA via parallel reverse transcription and amplification of the DNA obtained from reverse transcription, reagents necessary for both reactions may also comprise a reporter agent, may yield a detectable signal that is indicative of the presence of the amplified DNA product, and / or the target RNA amplified. The intensity of the detectable signal may be proportional to the amount of the amplified DNA product and / or the original target RNA amplified. The use of a reporter agent also enables real-time amplification methods, including real-time PCR for DNA amplification.

[0163] Reporter agents may be linked with nucleic acids, including amplified products, by covalent or non-covalent linkages or interactions. Examples of non-covalent linkates or interactions include ionic interactions, Van der Waals forces, hydrophobic interactions, hydrogen bonding, and combinations thereof. In some embodiments, reporter agents may bind to initial reactants and changes in reporter agent levels may be used to detect amplified product. In some embodiments, reporter agents may only be detectable (or non-detectable) as nucleic acid amplification progresses. In some embodiments, an optically-active dye (e.g., a fluorescent dye) may be used as may be used as a reporter agent. Examples of dyes include SYBR green, SYBR blue, DAPI, propidium iodine, Hoeste, SYBR gold, ethidium bromide, acridines, proflavine, acridine orange, acriflavine, fluorcoumanin, ellipticine, daunomycin, chloroquine, distamycin D, chromomycin, homidium, mithramycin, ruthenium polypyridyls, anthramycin, phenanthridines and acridines, ethidium bromide, propidium iodide, hexidium iodide, dihydroethidium, ethidium homodimer-1 and -2, ethidium monoazide, and ACMA, Hoechst 33258, Hoechst 33342, Hoechst 34580, DAPI, acridine orange, 7-AAD, actinomycin D, LDS751, hydroxystilbamidine, SYTOX Blue, SYTOX Green, SYTOX Orange, POPO-1, POPO-3, YOYO-1, YOYO-3, TOTO-1, TOTO-3, JOJO-1, LOLO-1, BOBO-1, BOBO-3, PO-PRO-1, PO-PRO-3, BO-PRO-1, BO-PRO-3, TO-PRO-1, TO-PRO-3, TO-PRO-5, JO-PRO-1, LO-PRO-1, YO-PRO-1, YO-PRO-3, PicoGreen, OliGreen, RiboGreen, SYBR Gold, SYBR Green I, SYBR Green II, SYBR DX, SYTO-40, -41, -42, -43, -44, -45 (blue), SYTO-13, -16, -24, -21, -23, -12, -11, -20, -22, -15, -14, -25 (green), SYTO-81, -80, -82, -83, -84, -85 (orange), SYTO-64, -17, -59, -61, -62, -60, -63 (red), fluorescein, fluorescein isothiocyanate (FITC), tetramethyl rhodamine isothiocyanate (TRITC), rhodamine, tetramethyl rhodamine, R-phycoerythrin, Cy-2, Cy-3, Cy-3.5, Cy-5, Cy5.5, Cy-7, Texas Red, Phar-Red, allophycocyanin (APC), Sybr Green I, Sybr Green II, Sybr Gold, CellTracker Green, 7-AAD, ethidium homodimer I, ethidium homodimer II, ethidium homodimer III, ethidium bromide, umbelliferone, eosin, green fluorescent protein, erythrosin, coumarin, methyl coumarin, pyrene, malachite green, stilbene, lucifer yellow, cascade blue, dichlorotriazinylamine fluorescein, dansyl chloride, fluorescent lanthanide complexes such as those including europium and terbium, carboxy tetrachloro fluorescein, 5 and / or 6-carboxy fluorescein (FAM), 5- (or 6-) iodoacetamidofluorescein, 5-{[2 (and 3)-5-(Acetylmercapto)-succinyl]amino}fluorescein (SAMSA-fluorescein), lissamine rhodamine B sulfonyl chloride, 5 and / or 6 carboxy rhodamine (ROX), 7-aminomethyl-coumarin, 7-Amino-4-methylcoumarin-3-acetic acid (AMCA), BODIPY fluorophores, 8-methoxypyrene-1,3,6-trisulfonic acid trisodium salt, 3,6-Disulfonate-4-amino-naphthalimide, phycobiliproteins, AlexaFluor 350, 405, 430, 488, 532, 546, 555, 568, 594, 610, 633, 635, 647, 660, 680, 700, 750, and 790 dyes, DyLight 350, 405, 488, 550, 594, 633, 650, 680, 755, and 800 dyes, or other fluorophores.

[0164] In some embodiments, a reporter agent may be a sequence-specific oligonucleotide probe that is optically active when hybridized with an amplified product. Due to sequence-specific binding of the probe to the amplified product, use of oligonucleotide probes can increase specificity and sensitivity of detection. A probe may be linked to any of the optically-active reporter agents (e.g., dyes) and may also include a quencher capable of blocking the optical activity of an associated dye. Examples of probes that may be useful used as reporter agents include TaqMan probes, TaqMan Tamara probes, TaqMan MGB probes, or Lion probes. In some embodiments, a reporter agent may be a radioactive species. Examples of radioactive species include 14C, 123I, 124I, 125I, 131I, 99mTc, 35S, or 3H. In some embodiments, a reporter agent may be an enzyme that is capable of generating a detectable signal. Detectable signal may be produced by activity of the enzyme with its substrate or a particular substrate in the case the enzyme has multiple substrates. Examples of enzymes that may be used as reporter agents include alkaline phosphatase, horseradish peroxidase, I2-galactosidase, alkaline phosphatase, β-galactosidase, acetylcholinesterase, and luciferase.

[0165] In some embodiments, an amplified product (e.g., amplified DNA product, amplified RNA product) may be detected. Detection of amplified product, including amplified DNA, may be accomplished with any suitable detection method. The particular type of detection method used may depend, for example, on the particular amplified product, the type of reaction vessel used for amplification, other reagents in a reaction mixture, whether or not a reporter agent was included in a reaction mixture, and if a reporter agent was used, the particular type of reporter agent use. Examples of detection methods include optical detection, spectroscopic detection, electrostatic detection, electrochemical detection, and the like. Optical detection methods include, but are not limited to, fluorimetry and UV-vis light absorbance. Spectroscopic detection methods include, but are not limited to, mass spectrometry, nuclear magnetic resonance (NMR) spectroscopy, and infrared spectroscopy. Electrostatic detection methods include, but are not limited to, gel based techniques, such as, for example, gel electrophoresis, SDS-PAGE gel. Electrochemical detection methods include, but are not limited to, electrochemical detection of amplified product after high-performance liquid chromatography separation of the amplified products.

[0166] In some embodiments, the time required to complete the elements of a method may vary depending upon the particular steps of the method. In some embodiments, an amount of time for completing the elements of a method may be from about 5 min to about 120 min. In some embodiments, an amount of time for completing the elements of a method may be from about 5 min to about 60 min. In some embodiments, an amount of time for completing the elements of a method may be from about 5 min to about 30 min. In some embodiments, an amount of time for completing the elements of a method may be less than or equal to 120 min, less than or equal to 90 min, less than or equal to 75 min, less than or equal to 60 min, less than or equal to 45 min, less than or equal to 40 min, less than or equal to 35 min, less than or equal to 30 min, less than or equal to 25 min, less than or equal to 20 min, less than or equal to 15 min, less than or equal to 10 min, or less than or equal to 5 min.

[0167] In some embodiments, the reaction may have a pH suitable for producing the product, for primer extension, protein expression, PCR amplication, or template jumping. In some embodiments, the pH of the reaction may range from about 5 to about 9, from about 6 to about 9, from about 7 to about 9, from about 8 to about 9. In some embodiments, the pH range is from about pH 2 to about pH 10, from about pH 4 to about pH 10, from about pH 2 to about pH 8, from about pH 4 to about pH 8, from about pH 5 to about pH 8, from about pH 5 to about pH 7, from about pH 6 to about pH 11, from about pH 6 to about pH 12, from about pH 5 to pH 13, from about pH 5 to about pH 14. In some embodiments, the pH is about 2.0, about 2.5, about 3.0, about 3.5, about 4.0, about 4.5, about 5.0, about 5.5, about 6.0, about 6.5, about 7.0, about 7.5, about 8.0, about 8.5, about 9.0, about 9.5, about 10.0, about 10.5, about 11, about 11.5, about 12, about 12.5, about 13, about 13.5, about 14.

[0168] In some embodiments, any method described herein may comprise a detergent. In some embodiments, the detergent is non-ionic and / or a zwitterionic detergent. In some embodiments, a non-ionic detergent is selected from a group consisting of tween, triton, Triton CF-21, Triton CF-32, Triton DF-12, Triton DF-16, Triton GR-SM, Triton N-101 (Polyoxyethylene branched nonylphenyl ether), Triton QS-15, Triton QS-44, Triton RW-75 (Polyethylene glycol 260 monoChexadecyl / octadecyl) ether and 1-Octadecanol), Triton X-100 (Polyethylene glycol tert-octylphenyl ether), Triton X-102, Triton X-15, Triton X-151, Triton X-200, Triton X-207, Triton X-114, Triton X-165, Triton X-305, Triton X-405 (polyoxyethylene(40) isooctylphenyl ether), Triton X-405 reduced (polyoxyethylene(40) isooctylcyclohexyl ether), Triton X-45 (Polyethylene glycol 4-tert-octylphenyl ether), Triton X-705-70, TWEEN in any form including: TWEEN 20 (Polyoxyethylene sorbitan monolaurate), TWEEN 21 (Polyoxyethylene sorbitan monolaurate), TWEEN 40 (polyoxyethylene(20) sorbitan monopalmitate), TWEEN 60 (Polyethylene glycol sorbitan monostearate), TWEEN 61 (Polyethylene glycol sorbitan monostearate), TWEEN 65 (Polyoxyethylene sorbitan Tristearate), TWEEN 80 (Polyoxyethylene sorbitan monooleate), TWEEN 81 (Polyoxyethylene sorbitan monooleate), TWEEN 85 (polyoxyethylene(20) sorbitan trioleate), Brij, Brij 30 (Polyoxyethylene 4 lauryl ether) Brij 35 (Polyoxyethylene 23 lauryl ether), Brij 52 (Polyoxyethylene 2 cetyl ether), Brij56 (Polyoxyethylene 10 cetyl ether), Brij 58 (Polyoxyethylene 20 cetyl ether), Brij 72 (Polyoxyethylene 2 stearyl ether), Brij 76 (Polyoxyethylene 10 stearyl ether), Brij 78 (Polyoxyethylene 20 stearyl ether), Brij 92 (Polyoxyethylene 2 oleyl ether), Brij 97 (Polyoxyethylene 10 oleyl ether), Brij 98 (Polyoxyethylene 20 oleyl ether), Brij700 (Polyoxyethylene 100 stearyl ether, octyl thioglucoside, maltosides, and combinations thereof

[0169] In some embodiments, any method described herein for producing any molecule as described herein comprises at least one salt. In some embodiments, the salt is at least one member selected from the group consisting of NaCl, LiCl, AlCl 3 , CuCl 2 , MgCl 2 , InCl 3 , SnCl 4 , CrCl 2 ,CrCl 3 , KCl, NaI, KI, TMACl (tetramethyl ammonium chloride), TEACl (tetraethyl ammonium chloride), KSCN, CsSCN, KCH 3 COO, CH 3 COONa, C 5 H 8 KNO 4 ,C 5 H 8 NNaO 4 , CsCl, and any combination thereof. In some embodiments, any method described herein for producing any molecule as described herein comprises NaCl. In some embodiments, the conditions sufficient for producing a molecule or a library comprises NaCl. In some embodiments, the reaction may have a salt concentration and / or NaCl suitable for producing a product, for primer extension, protein expression, PCR amplication, or template jumping. In some embodiments, the NaCl concentration is from about 50 mM to about 1000 mM, from about 100 mM to about 500 mM, from about 200 mM to about 300 mM, from about 200 mM to about 600 mM. In some embodiments, the NaCl concentration is at least about, at most about, or about 50 mM, at least about, at most about, or about 100 mM, at least about, at most about, or about 150 mM, at least about, at most about, or about 200 mM, at least about, at most about, or about 250 mM, at least about, at most about, or about 300 mM, at least about, at most about, or about 350 mM, at least about, at most about, or about 400 mM, at least about, at most about, or about 450 mM, at least about, at most about, or about 500 mM, at least about, at most about, or about 550 mM, at least about, at most about, or at least about, at most about, or about 600 mM, at least about, at most about, or about 650 mM, at least about, at most about, or about 700 mM, at least about, at most about, or about 750 mM, at least about, at most about, or about 800 mM, at least about, at most about, or about 850 mM, at least about, at most about, or about 900 mM, at least about, at most about, or about 950 mM, or at least about, at most about, or about 1000 mM. In some embodiments, the NaCl may improve enzyme activity and / or template jumping of an enzyme or polypeptide as described herein (e.g., of a reverse transcriptase).

[0170] In some embodiments, the reaction may have a nucleotide (e.g. dNTPs) concentration suitable for producing a product, for primer extension, protein expression, PCR amplication, or template jumping. In some embodiments, the total dNTP concentration in a reaction may be from about 50 µM to about 1000 µM, from about 100 µM to about 500 µM, from about 200 µM to about 300 µM, from about 200 µM to about 600 µM. In some embodiments, the total dNTP concentration is at least about, at most about, or about 50 µM, at least about, at most about, or about 100 µM, at least about, at most about, or about 150 µM, at least about, at most about, or about 200 µM, at least about, at most about, or about 250 µM, at least about, at most about, or about 300 µM, at least about, at most about, or about 350 µM, at least about, at most about, or about 400 µM, at least about, at most about, or about 450 µM, at least about, at most about, or about 500 µM, at least about, at most about, or about 550 µM, at least about, at most about, or at least about, at most about, or about 600 µM, at least about, at most about, or about 650 µM, at least about, at most about, or about 700 µM, at least about, at most about, or about 750 µM, at least about, at most about, or about 800 µM, at least about, at most about, or about 850 µM, at least about, at most about, or about 900 µM, at least about, at most about, or about 950 µM, or at least about, at most about, or about 1000 µM. In some embodiments, the total concentration of each dNTP is at least about, at most about, or about 1 µM; at least about, at most about, or about 2 µM; at least about, at most about, or about 3 µM; at least about, at most about, or about 4 µM; at least about, at most about, or about 5 µM; at least about, at most about, or about 6 µM; at least about, at most about, or about 7 µM; at least about, at most about, or about 8 µM; at least about, at most about, or about 9 µM; at least about, at most about, or about 10 µM; at least about, at most about, or about 15 µM; at least about, at most about, or about 20 µM; at least about, at most about, or about 25 µM; at least about, at most about, or about 30 µM; at least about, at most about, or about 35 µM; at least about, at most about, or about 40 µM; at least about, at most about, or about 45 µM; at least about, at most about, or about 50 µM; at least about, at most about, or about 55 µM; at least about, at most about, or about 60 µM; at least about, at most about, or about 65 µM; at least about, at most about, or about 70 µM; at least about, at most about, or about 75 µM; at least about, at most about, or about 80 µM; at least about, at most about, or about 85 µM; at least about, at most about, or about 90 µM; at least about, at most about, or about 95 µM; at least about, at most about, or about 100 µM; at least about, at most about, or about 250 µM; at least about, at most about, or about 500 µM; at least about, at most about, or about 1000 µM; at least about, at most about, or about 10000 µM. In some embodiments, the total concentration of each dNTP is from about 2 µM to about 5 µM, from about 2 µM to about 10 µM, from about 2 µM to about 20 µM, from about 2 µM to about 50 µM, from about 2 µM to about 100 µM, from about 2 µM to about 250 µM, from about 5 µM to about 10 µM, from about 5 µM to about 50 µM, from about 5 µM to about 250 µM, from about 5 µM to about 1000 µM.

[0171] In some embodiments, the concentration of each dNTP may be independent and different from the concentration of one or more dNTP. In some embodiments, the concentration of each dNTP for example the concentration of each dCTP, dGTP, dTTP, or dATP may be independent and different from the concentration of at least one other dNTP. In some embodiments, the concentration of one dNTP (e.g., dCTP, dGTP, dTTP, or dATP) may be at least about or at most about or about 1 fold, 2 fold, 3 fold, 4 fold, 5 fold, 7 fold, 10 fold, 20 fold, 35 fold, 50 fold, 75 fold, 90 fold, 100 fold, 200 fold, 500 fold, or 1000 fold different from at least one other dNTP (e.g., dCTP, dGTP, dTTP, or dATP).

[0172] In some embodiments, the reaction mixture includes a pH adjusting agent. pH adjusting agents of interest include, but are not limited to, sodium hydroxide, hydrochloric acid, phosphoric acid buffer solution, tris buffer, citric acid buffer solution, and the like. For example, the pH of the reaction mixture can be adjusted to the desired range by adding an appropriate amount of the pH adjusting agent.

[0173] The temperature range suitable for production of a product may vary according to factors such as the particular polymerase employed, and the melting temperatures of any optional primers employed. In some embodiments, the polymerase may include, but it is not limited to, a reverse transcriptase, a Moloney Murine Leukemia Virus (MMLV) reverse transcriptase, an R2 reverse transcriptase, an RNA-directed DNA polymerase, an DNA-directed DNA polymerase, a non-LTR retrotransposon, an R2 non-LTR retrotransposon, a polypeptide having reverse transcriptase activity, or any variant thereof, or any combination thereof.

[0174] In some embodiments, the conditions sufficient to produce a product include bringing the reaction mixture to a temperature ranging from about 4 °C to about 72 °C, from about 16 °C to about 70 °C, from about 37 °C to about 50°C, from about 40 °C to about 45 °C, from about 30 °C to about 42 °C, from about 25 °C to about 42 °C, from about 25 °C to about 30 °C, from about 28 °C to about 32 °C, from about 29 °C to about 31 °C. In some embodiments, the temperature is about 15 °C, about 16 °C, about 17 °C, about 18 °C, about 19 °C, about 20 °C, about 21 °C, about 22 °C, about 23 °C, about 24 °C, about 25 °C, about 26 °C, about 27 °C, about 28 °C, about 29 °C, about 30 °C, about 31 °C, about 32 °C, about 33 °C, about 34 °C, about 35 °C, about 36 °C, about 37 °C, about 38 °C, about 39 °C, about 40 °C, about 41 °C, about 42 °C, about 43 °C, about 44 °C, about 45 °C, about 46 °C, about 47 °C, about 48 °C, about 49 °C, about 50 °C, about 51 °C, about 52 °C, about 53 °C, about 54 °C, about 55 °C, about 56 °C, about 57 °C, about 58 °C, about 59 °C, about 60 °C, about 61 °C, about 62 °C, about 63 °C, about 64 °C, about 65 °C, about 66 °C, about 67 °C, about 68 °C, about 69 °C, about 70 °C, about 71 °C, about 72 °C, about 73 °C, about 74 °C, or about 75 °C. In some embodiments, the temperature is about or at most about 42 °C. In some embodiments, the temperature is about or at most about 50 °C. In some embodiments, the temperature is about or at most about 35 °C. In some embodiments, the temperature is about or at most about 25 °C. In some embodiments, the temperature is about or at most about 30 °C. In some embodiments, the reaction is incubated from about 20 min to about 3 h, from about 30 min to about 1.5 h, from about 30 min to about 1 h, from about 30 min to about 2 h, from about 1 h to about 2 h, from about 1 h to about 1.5 h, from about 30 min to about 5 h, from about 1 h to about 3 h, from about 1 h to about 4 h, from about 1 h to about 5 h. In some embodiments, the reaction is incubated for about 1 h. In some embodiments, the reaction is incubated for about 20 min, about 30 min, about 40 min, about 50 min, about 1 h, about 1.5 h, about 2 h, about 2.5 h, about 3 h, about 3.5 h, about 4 h, about 4.5 h, or about 5 h. In some embodiments, the reaction is incubated for at least at least about 20 min, at least about 30 min, at least about 40 min, at least about 50 min, at least about 1 h, at least about 1.5 h, at least about 2 h, at least about 2.5 h, at least about 3 h, at least about 3.5 h, at least about 4 h, at least about 4.5 h, or at least about 5 h. In some embodiments, the reaction is incubated at about 30 °C for about 1 h, or at about 42 °C for about 1 h. In some embodiments, the conditions sufficient for generating a molecule or a nucleic acid molecule comprises a temperature of about 12 °C to about 42 °C for about 1 min to about 5 h. In some embodiments, the conditions sufficient for generating a molecule or a nucleic acid molecule comprises a temperature of about 8 °C to about 50 °C for about 1 min to about 24 h.

[0175] In some embodiments, a primer can be designed to be a certain length. In some embodiments, a primer can be from about 6 to about 100 nucleotides, from about 6 to about 90 nucleotides, from about 6 to about 80 nucleotides, from about 6 to about 70 nucleotides, from about 6 to about 60 nucleotides, from about 6 to about 50 nucleotides, from about 6 to about 40 nucleotides, from about 6 to about 30 nucleotides, from about 6 to about 20 nucleotides, or from about 6 to about 10 nucleotides in length. In some embodiments, a primer can be from about 25 to about 80, from about 25 to about 75, from about 25 to about 70, from about 25 to about 65, from about 25 to about 60, from about 25 to about 55, from about 25 to about 50, from about 25 to about 45, from about 25 to about 40, from about 25 to about 35, or from about 25 to about 30 bases in length. In some embodiments, a primer can be at least about 5, at least about 6, at least about 7, at least about 8, at least about 9, at least about 10, at least about 11, at least about 12, at least about 13, at least about 14, at least about 15, at least about 16, at least about 17, at least about 18, at least about 19, at least about 20, at least about 25, at least about 30, at least about 35, at least about 40, at least about 45, at least about 50, at least about 55, at least about 60, at least about 65, at least about 70, at least about 75, at least about 80, at least about 85, at least about 90, at least about 95 or at least about 100 bases in length. In some embodiments, a primer can be about 5, about 6, about 7, about 8, about 9, about 10, about 11, about 12, about 13, about 14, about 15, about 16, about 17, about 18, about 19, about 20, about 25, about 30, about 35, about 40, about 45, about 50, about 55, about 60, about 65, about 70, about 75, about 80, about 85, about 90, about 95 or about 100 bases in length. In some embodiments, a primer can be at least about, no more than about, or about 120, 130, 140, 150, 160, 170, 180, 190, 200, 230, 250, 270, 290, 300, 320, 340, 350, 370, 400, 420, 450, 470, 490, or 500.

[0176] In some embodiments, a primer can be designed to anneal to a target at a given melting temperature (Tm). In some embodiments, a Tm can be from about 20 °C to about 100 °C, about 20 °C to about 90 °C, about 20 °C to about 80 °C, about 20 °C to about 70 °C, about 20 °C to about 60 °C, about 20 °C to about 50 °C, about 20 °C to about 40 °C, or about 20 °C to about 30 °C. In some embodiments, a Tm can be at least about, at most about, or about 20 °C, 21 °C, 22 °C, 23 °C, 24 °C, 25 °C, 26 °C, 27 °C, 28 °C, 29 °C, 30 °C, 31 °C, 32 °C, 33 °C, 34 °C, 35 °C, 36 °C, 37 °C, 38 °C, 39 °C, 40 °C, 41 °C, 42 °C, 43 °C, 44 °C, 45 °C, 46 °C, 47 °C, 48 °C, 49 °C, 50 °C, 51 °C, 52 °C, 53 °C, 54 °C, 55 °C, 56 °C, 57 °C, 58 °C, 59 °C, 60 °C, 61 °C, 62 °C, 63 °C, 64 °C, 65 °C, 66 °C, 67 °C, 68 °C, 69 °C, 70 °C, 71 °C, 72 °C, 73 °C, 74 °C, 75 °C, 76 °C, 77 °C, 78 °C, 79 °C, 80 °C, 81 °C, 82 °C, 83 °C, 84 °C, 85 °C, 86 °C, 87 °C, 88 °C, 89 °C, 90 °C, 91 °C, 92 °C, 83 °C, 84 °C, 85 °C, 96 °C, 97 °C, 98 °C, 99 °C, or 100 °C. A plurality of primers can be designed to have Tms within a range, e.g., within a range spanning 15 °C, 10 °C, 9 °C, 8 °C, 7 °C, 6 °C, 5 °C, 4 °C, 3 °C, 2 °C, or 1 °C. A plurality of primers can be designed to have identical Tms.

[0177] In some embodiments the enzyme, or modified enzyme (e.g., modified reverse transcriptase), or protein, or polypeptide, or a variant, or a PCR product, or a cDNA molecule, or a template, or a nucleic acid molecule, or any component as described herein may be purified. In some embodiments, the fragmented or degraded nucleic acid (e.g., RNA or DNA) may be purified. In some embodiments, the reverse transcriptase or a modified reverse transcriptase may be purified. In some embodiments, the R2 reverse transcriptase or a modified R2 reverse transcriptase may be purified. In some embodiments, the non-LTR retrotransposon protein or polypeptide having reverse transcriptase activity, or a modified non-LTR retrotransposon protein or a modified polypeptide having reverse transcriptase activity may be further purified. In some embodiments, the cDNA molecule may be purified. In some embodiments, the template may be purified. In some embodiments, the acceptor nucleic acid molecule may be purified.

[0178] Purification may comprise precipitation, ultracentrifugation, chromatographic method based on size, charge, hydrophobicity, affinity, metal binding, HPLC. In some embodiments, the purification comprises column chromatography. In some embodiments, the column chromatography may be size exclusion (SEC), ion exchange (IEX), affinity chromatography, immobilized metal ion affinity chromatography (IMAC), Ni-IMAC chromatography, and / or hydrophobic interaction (HIC). In some embodiments, the purification comprises His-tag affinity resin. In some embodiments, the purification may comprise one step. In some embodiments, the purification may comprise two steps. In some embodiments, the two step purification comprises nickel and heparin. In some embodiments, the two step purification comprises nickel and heparin affinity purifications. In some embodiments, the two purification steps provide higher activity and / or increased template jumping compared to one step purification. In some embodiments, the purification comprises heparin-affinity purification. In some embodiments, purification may include affinity purification, Ni-NTA affinity, fast protein liquid chromatography (FPLC) (e.g., AKTA and Bio-Rad FPLC systems), high-pressure liquid chromatography (HPLC) (e.g., Beckman and Waters HPLC). In some embodiments, purification may include ion exchange chromatography (e.g., Q, S), size exclusion chromatography, salt gradients, affinity purification (e.g., Ni, Co, FLAG, maltose, glutathione, protein A / G), gel filtration, reverse-phase, ceramic HYPERD (Registered trademark) ion exchange chromatography, and hydrophobic interaction columns (HIC). Also included are analytical methods such as SDS-PAGE (e.g., coomassie, silver stain), immunoblot, Bradford, and ELISA, which may be utilized during any step of the production or purification process, typically to measure the purity of the protein or enzyme composition.

[0179] In some embodiments, the overall activity of the purified enzyme, protein, polypeptide, the R2 reverse transcriptase, the non-LTR retrotransposon protein or polypeptide having reverse transcriptase activity, the reverse transcriptase, or variants thereof, or products thereof using a two-step purification is at least about 2%, at least about 5%, at least about 7%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95%, at least about 98%, at least about 99% higher than the overall activity using the one-step purification. In some embodiments, the overall activity of the purified enzyme, protein, polypeptide, the R2 reverse transcriptase, the non-LTR retrotransposon protein or polypeptide having reverse transcriptase activity, the reverse transcriptase, or variants thereof, or products thereof is at least about 0.5%, at least about 1%, at least about 1.5%, at least about 2%, at least about 5%, at least about 7%, at least about 10%, at least about 15%, at least about 20%, at least about 25%, at least about 30%, at least about 35%, at least about 40%, at least about 45%, at least about 50%, at least about 55%, at least about 60%, at least about 65%, at least about 70%, at least about 75%, at least about 80%, at least about 85%, at least about 90%, at least about 95%, at least about 98%, at least about 99% higher than the overall activity of the non-purified enzyme, protein, polypeptide, R2 reverse transcriptase, non-LTR retrotransposon protein or polypeptide having reverse transcriptase activity, reverse transcriptase, or variants thereof, or products thereof. In some embodiments, a purified enzyme, protein, polypeptide, R2 reverse transcriptase, the non-LTR retrotransposon protein, or polypeptide having reverse transcriptase activity, reverse transcriptase, modified enzyme, modified reverse transcriptase, modified polypeptide having reverse transcriptase activity, or variants thereof, or products thereof is at least about 0.5%, at least about 1%, at least about 3%, at least about or about 5%, at least about or about 10%, at least about or about 15%, at least about or about 20%, at least about or about 25%, at least about or about 30%, at least about or about 35%, at least about or about 40%, at least about or about 45%, at least about or about 50%, at least about or about 55%, at least about or about 60%, at least about or about 61%, at least about or about 62%, at least about or about 63%, at least about or about 64%, at least about or about 65%, at least about or about 66%, at least about or about 67%, at least about or about 68%, at least about or about 69%, at least about or about 70%, at least about or about 71%, at least about or about 72%, at least about or about 73%, at least about or about 74%, at least about or about 75%, at least about or about 76%, at least about or about 77%, at least about or about 78%, at least about or about 79%, at least about or about 80%, at least about or about 81%, at least about or about 82%, at least about or about 83%, at least about or about 84%, at least about or about 85%, at least about or about 86%, at least about or about 87%, at least about or about 88%, at least about or about 89%, at least about or about 90%, at least about or about 91%, at least about or about 92%, at least about or about 93%, at least about or about 94%, at least about or about 95%, at least about or about 96%, at least about or about 97%, at least about or about 98%, or at least about or about 99% pure.

[0180] In some embodiments, the purified enzyme, protein, polypeptide, R2 reverse transcriptase, non-LTR retrotransposon protein or polypeptide having reverse transcriptase activity, reverse transcriptase, or variants thereof, or products thereof produces template jumping that is at least about or about one time, at least about or about two times, at least about or about three times, at least about or about four times, at least about or about five times, at least about or about six times, at least about or about seven times, at least about or about eight times, at least about or about nine times, at least about or about ten times, at least about or about fifteen times, at least about or about twenty times, at least about or about twenty five times, at least about or about thirty times, at least about or about forty times, at least about or about fifty times, at least about or about seventy times, at least about or about eighty times, at least about or about ninety times, at least about or about 100 times, at least about or about 150 times, at least about or about 200 times, at least about or about 250 times, at least about or about 300 times, at least about or about 350 times, at least about or about 400 times, at least about or about 500 times, at least about or about 700 times, at least about or about 1000 times, at least about or about 10000 times more and / or higher intensity than the non-purified enzyme, protein, polypeptide, R2 reverse transcriptase, non-LTR retrotransposon protein or polypeptide having reverse transcriptase activity, reverse transcriptase, or variants thereof, or products thereof.Cell-free DNA and circulating tumor DNA

[0181] In some embodiments, obtaining a quantity of circulating tumor (ctDNA) may comprise PCR. In some embodiments, obtaining a quantity of ctDNA may comprise digital PCR. In some embodiments, obtaining a quantity of ctDNA may comprise quantitative PCR. In some embodiments, obtaining a quantity of ctDNA may comprise obtaining sequencing information on the ctDNA. The sequencing information may comprise information relating to one or more genomic regions based. In some embodiments, obtaining the quantity of ctDNA may comprise hybridization of the ctDNA to an array.

[0182] Determining the quantity of the cell-free DNA may comprise determining absolute quantities of the cell-free DNA. The quantity of the cell-free DNA may be determined by counting sequencing reads pertaining to the cell-free DNA. The quantity of the cell-free DNA may be determined by quantitative PCR.

[0183] Determining quantities of cell-free DNA (cf DNA) may be performed by molecular barcoding of the cfDNA. Molecular barcoding of the cf DNA may comprise attaching adaptors to one or more ends of the cf DNA. The adaptor may comprise a plurality of oligonucleotides. The adaptor may comprise one or more deoxyribonucleotides. The adaptor may comprise ribonucleotides. The adaptor may be single-stranded. The adaptor may be double-stranded. The adaptor may comprise double-stranded and single-stranded portions. For example, the adaptor may be a Y-shaped adaptor. The adaptor may be a linear adaptor. The adaptor may be a circular adaptor. The adaptor may comprise a molecular barcode, sample index, primer sequence, linker sequence or a combination thereof. The molecular barcode may be adjacent to the sample index. The molecular barcode may be adjacent to the primer sequence. The sample index may be adjacent to the primer sequence. A linker sequence may connect the molecular barcode to the sample index. A linker sequence may connect the molecular barcode to the primer sequence. A linker sequence may connect the sample index to the primer sequence.

[0184] The adaptor may comprise a molecular barcode. The molecular barcode may comprise a random sequence. The molecular barcode may comprise a predetermined sequence. Two or more adaptors may comprise two or more different molecular barcodes. The molecular barcodes may be optimized to minimize dimerization. The molecular barcodes may be optimized to enable identification even with amplification or sequencing errors. For examples, amplification of a first molecular barcode may introduce a single base error. The first molecular barcode may comprise greater than a single base difference from the other molecular barcodes. Thus, the first molecular barcode with the single base error may still be identified as the first molecular barcode. The molecular barcode may comprise at least 2, 3, 4, 5, 6, 7, 8, 9, 10 or more nucleotides. The molecular barcode may comprise at least 3 nucleotides. The molecular barcode may comprise at least 4 nucleotides. The molecular barcode may comprise less than 20, 19, 18, 17, 16, or 15 nucleotides. The molecular barcode may comprise less than 10 nucleotides. The molecular barcode may comprise less than 8 nucleotides. The molecular barcode may comprise less than 6 nucleotides. The molecular barcode may comprise 2 to 15 nucleotides. The molecular barcode may comprise 2 to 12 nucleotides. The molecular barcode may comprise 3 to 10 nucleotides. The molecular barcode may comprise 3 to 8 nucleotides. The molecular barcode may comprise 4 to 8 nucleotides. The molecular barcode may comprise 4 to 6 nucleotides.

[0185] The adaptor may comprise a sample index. The sample index may comprise a random sequence. The sample index may comprise a predetermined sequence. Two or more sets of adaptors may comprise two or more different sample indexes. Adaptors within a set of adaptors may comprise identical sample indexes. The sample indexes may be optimized to minimize dimerization. The sample indexes may be optimized to enable identification even with amplification or sequencing errors. For examples, amplification of a first sample index may introduce a single base error. The first sample index may comprise greater than a single base difference from the other sample indexes. Thus, the first sample index with the single base error may still be identified as the first molecular barcode. The sample index may comprise at least 2, 3, 4, 5, 6, 7, 8, 9, 10 or more nucleotides. The sample index may comprise at least 3 nucleotides. The sample index may comprise at least 4 nucleotides. The sample index may comprise less than 20, 19, 18, 17, 16, or 15 nucleotides. The sample index may comprise less than 10 nucleotides. The sample index may comprise less than 8 nucleotides. The sample index may comprise less than 6 nucleotides. The sample index may comprise 2 to 15 nucleotides. The sample index may comprise 2 to 12 nucleotides. The sample index may comprise 3 to 10 nucleotides. The sample index may comprise 3 to 8 nucleotides. The sample index may comprise 4 to 8 nucleotides. The sample index may comprise 4 to 6 nucleotides.

[0186] The adaptor may comprise a primer sequence. The primer sequence may be a PCR primer sequence. The primer sequence may be a sequencing primer.

[0187] Adaptors may be attached to one end of the cf DNA. Adaptors may be attached to both ends of the cf DNA. Adaptors may be attached to one or more ends of a single-stranded cf DNA. Adaptors may be attached to one or more ends of a double-stranded cfDNA.

[0188] Adaptors may be attached to the cf DNA by ligation. Ligation may be blunt end ligation. Ligation may be sticky end ligation. Adaptors may be attached to the cf DNA by primer extension. Adaptors may be attached to the cf DNA by reverse transcription. Adaptors may be attached to the cf DNA by hybridization. Adaptors may comprise a sequence that is at least partially complementary to the cf DNA. Alternatively, in some instances, adaptors do not comprise a sequence that is complementary to the cf DNA.

[0189] The cf-DNA may be derived from a tumor in the subject. The cf-DNA may be derived from any sample of the subject. The cf-DNA may be derived from any organ of the subject. The cf-DNA may be derived from any liquid of the subject (e.g., blood, saliva, urine, and mucus). The method may further comprise detecting a cancer in the subject based on the detection of the cf-DNA.

[0190] In some embodiments, the presence or absence of a sequence can be linked to a DNA or RNA profile or to a cancer. For example, the presence or absence of a sequence, can be linked to a transcription profile, microRNA profile, cancer profile, or genomic mutation profile of a sample, such as a single cell. In some embodiments, cfDNA can be used for cancer profiling, and / or monitoring a condition progression, and / or monitoring the occurrence of previous and new mutations.The method may further comprise diagnosing a cancer in the subject based on the detection of the cf-DNA. Diagnosing the cancer may have a sensitivity of at least about 50%, 52%, 55%, 57%, 60%, 62%, 65%, 67%, 70%, 72%, 75%, 77%, 80%, 82%, 85%, 87%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, or 99%. Diagnosing the cancer may have a specificity of at least about 50%, 52%, 55%, 57%, 60%, 62%, 65%, 67%, 70%, 72%, 75%, 77%, 80%, 82%, 85%, 87%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, or 99%. The method may further comprise prognosing a cancer in the subject based on the detection of the cf-DNA. Prognosing the cancer may have a sensitivity of at least about 50%, 52%, 55%, 57%, 60%, 62%, 65%, 67%, 70%, 72%, 75%, 77%, 80%, 82%, 85%, 87%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, or 99%. Prognosing the cancer may have a specificity of at least about 50%, 52%, 55%, 57%, 60%, 62%, 65%, 67%, 70%, 72%, 75%, 77%, 80%, 82%, 85%, 87%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, or 99%. The method may further comprise determining a therapeutic regimen for the subject based on the detection of the cf-DNA. The method may further comprise administering an anti-cancer therapy to the subject based on the detection of the cf-DNA. The method may further comprise detecting mutations (e.g., mutations at specific regions) based on the sequencing information. Diagnosing the cancer may be based on the detection of mutations. The detection of at least 3 mutations may be indicative of the cancer. The detection of one or more mutations in three or more regions may be indicative of the cancer.Mutation of Enzymes

[0191] In some embodiments, a modified enzyme, or derivatives and variants may be prepared during synthesis of the peptide or by post-production modification. In some embodiments, a modified enzyme, or derivatives and variants may be produced by site-directed mutagenesis (e.g. Q5 ®< Site-Directed Mutagenesis Kit Protocol), random mutagenesis, or enzymatic cleavage and / or ligation of nucleic acids. In some embodiments, the derivatives and variants, or a modified enzyme are produced by random mutagenesis. In some embodiments, a rational design and / or mutagenesis is based on sequence alignment analysis. In some embodiments, the rational design / mutagenesis is based on sequence alignment analysis with defined and known enzymes and proteins. In some embodiments, sequence alignment analysis is performed with enzymes and / or elements with homology to R2, including non-LTR retrotransposons, telomerase, group II introns, LTR retrotransposons, reverse transcriptase, retroviral reverse transcriptase (e.g., HIV, MMLV), and viral RNA dependent RNA polymerase.

[0192] In some embodiments, variants or modified enzymes as described herein can be produced by, including for example, site-saturation mutagenesis, scanning mutagenesis, insertional mutagenesis, deletion mutagenesis, random mutagenesis, site-directed mutagenesis, and directed-evolution, as well as various other recombinatorial approaches. Methods for making modified enzymes, polynucleotides and proteins (e.g., variants) include DNA shuffling methodologies, methods based on non-homologous recombination of genes, such as ITCHY (See, Ostermeier et al., 7:2139-44

[1999] ), SCRACHY (See, Lutz et al. 98:11248-53

[2001] ), SHIPREC (See, Sieber et al., 19:456-60

[2001] ), and NRR (See, Bittker et al., 20:1024-9

[2001] ; Bittker et al., 101:7011-6

[2004] ), and methods that rely on the use of oligonucleotides to insert random and targeted mutations, deletions and / or insertions (See, Ness et al., 20:1251-5

[2002] ; Coco et al., 20:1246-50

[2002] ; Zha et al., 4:34-9

[2003] ; Glaser et al., 149:3903-13

[1992] ). In some embodiments, polynucleotides, polypeptides, proteins, or enzymes as described herein may be altered by being subjected to random mutagenesis by error-prone PCR, random nucleotide insertion or other methods prior to recombination. Polynucleotides, polypeptides, proteins, or enzymes as described herein may be produced by DNA shuffling, gene-shuffling, motif-shuffling, exon-shuffling, and / or codon-shuffling (collectively referred to as "DNA shuffling"). DNA shuffling involves the assembly of two or more DNA segments by homologous or site-specific recombination to generate variation in the polynucleotide sequence. DNA shuffling may be employed to modulate the activities of polynucleotides, polypeptides, proteins, or enzymes as described herein, such methods can be used to generate polypeptides with altered activity. See, generally, U.S. Pat. Nos. 5,605,793; 5,811,238; 5,830,721; 5,834,252; 5,837,458; and 6,444,468; and Patten et al., Curr. Opinion Biotechnol. 8:724-33 (1997); Harayama, Trends Biotechnol. 16(2):76-82 (1998); Hansson, et al., J. Mol. Biol. 287:265-76 (1999); and Lorenzo and Blasco, Biotechniques 24(2):308-13 (1998). Polynucleotides, polypeptides, proteins, or enzymes as described herein may contain one or more components, motifs, sections, parts, domains, and fragments, of a polynucleotide, polypeptide, protein, or enzyme as described herein. In some embodiments, kits for use in mutagenic PCR, such as, for example, the Diversify PCR Random Mutagenesis Kit (Clontech) or the GeneMorph Random Mutagenesis Kit (Stratagene) may be used.

[0193] In some embodiments, variant proteins differ from a parent protein or modified enzymes differ from a wild-type or unmodified enzyme and one another by a small number of amino acid residues. The number of differing amino acid residues may be one or more, preferably about 1, 2, 3, 4, 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 100 or more amino acid residues. In some embodiments, the number of different amino acids between variants is between about 1 and about 10. In some embodiments, related proteins and particularly variant proteins comprise at least about 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 97%, 98%, or 99% amino acid sequence identity. Additionally, a related protein or a variant protein as used herein, refers to a protein that differs from another related protein or a parent protein in the number of prominent regions. For example, in some embodiments, variant proteins have about 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 corresponding prominent regions that differ from the parent protein.

[0194] In some embodiments, screening methods can include conventional screening methods such as liquid phase, or microtiter plate based assays. The format for liquid phase assays is often robotically manipulated 96, 384, or 1536-well microtiter plates. Other screening methods include growth selection (Snustad et al., 1988; Lundberg et al., 1993; Yano et al., 1998), colorimetric screening of bacterial colonies or phage plaques (Kuritz, 1999), in vitro expression cloning (King et al., 1997) and cell surface or phage display (Benhar, 2001). In some embodiments, screening approaches may be a method selected from yeast-2-hybrid, n-hybrid, reverse-2-hybrid, reverse n-hybrid, split two hybrid, bacterial display, phage display, retroviral display, ribosome display, covalent display, in vitro display, or any other display method. In some embodiments, the library is screened using a phage display method.

[0195] Analysis of the sequences derived from template jumps: the band corresponding to the template jump product may be excised from a polyacrylamide gel, eluted with sodium acetate (e.g. 0.3 M sodium acetate, pH 5.2), SDS (e.g. 0.03%) for several h at room temperature, phenol / chloroform extracted and ethanol precipitated. The isolated cDNA may then be used as a template for PCR amplification using one or more primer(s). The PCR products may then be directly cloned into a vector (Burke et al.,"R4, a non-LTR Retrotransposon Specific to the Large Subunit rRNA Gene of Nematodes,"Nucleic Acids Res. 23: 4628-4634 (1995)) and individual clones sequenced.Kits

[0196] Any of the compositions described herein may be comprised in a kit. In a Example, the kit, in a suitable container, comprises one or more primer(s). The kit can also comprise a computer readable medium, e.g., non-transitory computer readable medium. The kit can also comprise reaction components for primer extension and amplification (e.g., dNTPs, polymerase, buffers). The kit can include reagents for library formation (e.g., primers (probes), dNTPs, polymerase, and enzymes). The kit may also comprise approaches for purification, such as a bead suspension. The kit can include reagents for sequencing, e.g., fluorescently labelled dNTPs, sequencing primers, etc.

[0197] In some embodiments, some of the components of the kit may be packaged either in aqueous media or in lyophilized form. The containers of the kits can include at least one vial, test tube, flask, bottle, syringe or other containers, into which a component may be placed and suitably aliquotted. Where there is more than one component in the kit, the kit also can contain a second, third or other additional container into which the additional components may be separately placed. Various combinations of components may be comprised in a container. In some embodiments, various combinations of components may be comprised in a vial. The kits described herein may also contain the components in close confinement for commercial sale. Such containers may include injection or blow molded plastic containers into which the desired vials are retained.

[0198] When the components of the kit are provided in one or more liquid solutions, the liquid solution can be an aqueous solution. The components of the kit may be provided as dried powder(s). When reagents and / or components are provided as a dry powder, the powder can be reconstituted by the addition of a suitable solvent.

[0199] A kit can include instructions for employing the kit components as well the use of any other reagent not included in the kit. Instructions may include variations that can be implemented.

[0200] In some embodiments, reagents and materials include primers for amplifying desired sequences, nucleotides, suitable buffers or buffer reagents, salt, and so forth, and in some cases the reagents include apparatus or reagents for isolation of a particular desired cell(s). In some embodiments, there are one or more apparatuses in the kit suitable for extracting one or more samples from an individual. The apparatus may be a syringe, fine needles, scalpel, and so forth.

[0201] In some embodiments, a kit may be used for the preparation of cDNA from a template (e.g. RNA template). Such a kit may include a carrier device compartmentalized to receive one or more containers, such as vials, tubes, and the like, each of which includes one of the separate elements used to prepare cDNA from RNA. For example, there may be provided a first container, the contents of which include a reverse transcriptase (e.g. non-retroviral reverse transcriptase, non-LTR retrotransposon, R2 reverse transcriptase) or variants thereof, in a liquid solution, powder form, or lyophilized form. Further, any number of additional containers can be provided, the contents of which independently include suitable buffers, substrates for nucleotide synthesis such as the deoxynucleotide triphosphates (e. g., dATP, dCTP, dGTP, and dTTP) either individually or collectively in a suitable solution, a template (e.g. template RNA), one or more primer(s), and acceptor nucleic acid molecule (e.g. acceptor RNA), and optionally a terminal transferase in solution. In some embodiments, a kit may comprise a fragment or degraded nucleic acid, DNA, RNA, or a combination thereof, one of more primer(s), an acceptor nucleic acid molecule (e.g., an acceptor nucleic acid molecule comprising a modified nucleotide), a reverse transcriptase (e.g., non-retroviral reverse transcriptase, non-LTR retrotransposon, R2 reverse transcriptase) or variants thereof, suitable buffers, substrates for nucleotide synthesis such as the deoxynucleotide triphosphates (e. g., dATP, dCTP, dGTP, and dTTP). Any combinations of the above components can be provided. Any of the above components may be excluded from the kit. In some embodiments, the one or more primer(s) may be one or more random primer(s). In some embodiments, any of the components may be individually packed.Target molecule

[0202] In some instances, the molecules are DNA, RNA, or DNA-RNA hybrids. The molecules may be single-stranded or double-stranded. In some embodiments, the molecules are RNA molecules, such as mRNA, rRNA, tRNA, ncRNA, lncRNA, siRNA, microRNA or miRNA. The RNA molecules may be polyadenylated. Alternatively, the mRNA molecules are not polyadenylated. Alternatively, the molecules are DNA molecules. The DNA molecules may be genomic DNA. The DNA molecules may comprise exons, introns, untranslated regions, or any combination thereof. In some embodiments, the molecules are a panel of molecules.

[0203] In some embodiments, the molecule is a fragment or degraded molecule. In some embodiments, the fragment or degraded molecule is a fragment DNA, degraded DNA, fragment RNA, degraded RNA, or combinations thereof. In some embodiments, the molecule is a template nucleic acid (e.g., template DNA, RNA, or combinations thereof). In some embodiments, the molecule is a nucleic acid. In some embodiments, the total amount of a molecule is from about 1 femtomolar (fM) to about 100 micromolar, from about 40 femtomolar to about 0.01 micromolar, from about 50 femtomolar to about 500 femtomolar, from about 50 femtomolar to about 0.01 micromolar, from about 50 femtomolar to about 0.1 micromolar, from about 50 femtomolar to about 500 picomolar, from about 50 femtomolar to about 500 nanomolar, from about 50 femtomolar to about 500 micromolar, from about 50 femtomolar to about 1 picomolar, from about 40 femtomolar to about 1 nanomolar, from about 1 femtomolar to about 1 picolomar, from about 0.1nM to about 100nM. In some embodiments, the total about of a molecule is equal to or lower than about 1000 micromolar, equal to or lower than about 500 micromolar, equal to or lower than about 250 micromolar, equal to or lower than about 100 micromolar, equal to or lower than about 50 micromolar, equal to or lower than about 25 micromolar, equal to or lower than about 10 micromolar, equal to or lower than about 1 micromolar, equal to or lower than about 0.1 micromolar, equal to or lower than about 0.01 micromolar, equal to or lower than about 0.001 micromolar, equal to or lower than about 0.0001 micromolar, equal to or lower than about 2000 nanomolar, equal to or lower than about 500 nanomolar, equal to or lower than about 250 nanomolar, equal to or lower than about 200 nanomolar, equal to or lower than about 50 nanomolar, equal to or lower than about 25 nanomolar, equal to or lower than about 20 nanomolar, equal to or lower than about 2 nanomolar, equal to or lower than about 0.2 nanomolar, equal to or lower than about 0.01 nanomolar, equal to or lower than about 0.001 nanomolar, equal to or lower than about 0.0001 nanomolar, equal to or lower than about 3000 picomolar, equal to or lower than about 500 picomolar, equal to or lower than about 250 picomolar, equal to or lower than about 300 picomolar, equal to or lower than about 50 picomolar, equal to or lower than about 25 picomolar, equal to or lower than about 30 picomolar, equal to or lower than about 3 picomolar, equal to or lower than about 0.3 picomolar, equal to or lower than about 0.01 picomolar, equal to or lower than about 0.001 picomolar, equal to or lower than about 0.0001 picomolar, equal to or lower than about 5000 femtomolar, equal to or lower than about 500 femtomolar, equal to or lower than about 250 femtomolar, equal to or lower than about 50 femtomolar, equal to or lower than about 25 femtomolar, equal to or lower than about 10 femtomolar, equal to or lower than about 1 femtomolar, equal to or lower than about 0.1 femtomolar, equal to or lower than about 0.01 femtomolar, equal to or lower than about 0.001 femtomolar, equal to or lower than about 0.0001 femtomolar.

[0204] The methods and kits described herein may be used to stochastically label individual occurrences of identical or nearly identical molecules and / or different molecules. In some instances, the methods and kits described herein may be used to stochastically label identical or nearly identical molecules (e.g., molecules comprise identical or nearly identical sequences). For example, the molecules to be labeled comprise at least about 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, or 100% sequence identity. The nearly identical molecules may differ by less than about 100, 90, 80, 70, 60, 50, 40, 30, 25, 20, 25, 10, 9, 8, 7, 6, 5, 4, 3, 2, or 1 nucleotide or base pair. The plurality of nucleic acids in one or more samples of the plurality of samples may comprise two or more identical sequences. At least about 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 97%, or 100% of the total nucleic acids in one or more of the plurality of samples may com...

Claims

1. A method for preparing a complementary deoxyribonucleic acid molecule library comprising: (a) annealing one or more primers to an amount of template nucleic acid molecules, thereby generating one or more annealed template nucleic acid molecules; and (b) mixing, in the presence of nucleotides: i. said one or more annealed template nucleic acid molecules; ii. one or more RNA template_acceptor nucleic acid molecules; and iii. a modified reverse transcriptase derived from Bombyx mori, whereby said modified reverse transcriptase generates a plurality of continuous complementary deoxyribonucleic acid molecule by reverse transcribing a sequence of an annealed template nucleic acid molecule, migrating to an acceptor nucleic acid molecule, and reverse transcribing a sequence of said acceptor nucleic acid molecule without thermal cycling in a single reaction vessel.

2. The method of claim 1, wherein said modified reverse transcriptase comprises at least one improved enzyme property relative to a wild type unmodified reverse transcriptase, said improved enzyme property being selected from: higher thermo-stability, higher specific activity, higher processivity, higher strand displacement, higher end-to-end template jumping, higher affinity, and higher fidelity relative to said wild type unmodified reverse transcriptase.

3. The method of claim 1, wherein said modified reverse transcriptase is an R2 reverse transcriptase.

4. The method of claim 1, wherein said modified reverse transcriptase has at least 90% identity to SEQ ID NO: 49, SEQ ID NO: 50, SEQ ID NO: 51, SEQ ID NO: 52, SEQ ID NO: 53, SEQ ID NO: 54, SEQ ID NO: 55, SEQ ID NO: 56, SEQ ID NO: 57, SEQ ID NO: 58, SEQ ID NO: 59, SEQ ID NO: 60, SEQ ID NO: 61, SEQ ID NO: 62, SEQ ID NO: 63, SEQ ID NO: 64, SEQ ID NO: 65, SEQ ID NO: 66, or SEQ ID NO: 67 and contains at least one substitution modification relative to SEQ ID NO:52.

5. The method of claim 1, further comprising adding a tag to said amount of template nucleic acid molecules, thereby generating a plurality of tagged continuous complementary deoxyribonucleic acid molecules after performing steps a) and b), and optionally, further comprising sequencing said plurality of tagged continuous complementary deoxyribonucleic acid molecules.

6. The method of claim 1, wherein said modified reverse transcriptase further comprises a tag, said tag being selected from biotin, azido group, acetylene group, His-tag, calmodulin-tag, CBP, CYD, Strep II, FLAG-tag, HA-tag, Myc-tag, S-tag, SBP-tag, Softag-1, Softag-3, V5-tag, Xpress-tag, isopeptag, SpyTag B, HPC peptide tags, GST, MBP, biotin carboxyl carrier protein, glutathione-S-transferase-tag, green fluorescent protein-tag, maltose binding protein- tag, Nus-tag, Strep-tag, and thioredoxin-tag.

7. The method of claim 1, wherein said one or more acceptor nucleic acid molecules comprises a modified nucleotide that stops the reverse transcription by said modified reverse transcriptase.

8. The method of claim 1, further comprising obtaining a sample from a subject, said sample comprising one or more cell free nucleic acids, and the method further comprises performing the reaction of (a) and (b) in the same vessel.

9. The method of claim 1, further comprising depleting at least one ribosomal RNA (rRNA) from said one or more template nucleic acid molecules prior to annealing one or more primers, optionally wherein the step for depleting said at least one ribosomal RNA (rRNA) comprises hybridization of an oligonucleotide to said rRNA, or optionally wherein the step for depleting said at least one ribosomal RNA (rRNA) comprises an oligonucleotide probe-guided endonucleolitic cleavage of said rRNA.

10. The method of claim 1, further comprising depleting at least one transfer RNA (tRNA) from said amount of template nucleic acid molecules prior to annealing one or more primers.

11. The method of claim 1, wherein said method is performed in the absence of purification of said one or more annealed template nucleic acid molecules.

12. The method of claim 1, further comprising purifying said mixture comprising said plurality of continuous complementary deoxyribonucleic acid molecules, optionally wherein said purifying comprises two purification steps, and optionally wherein said two purification steps comprise a nickel and a heparin affinity purification step.

13. The method of claim 1, wherein said one or more primers comprise one or more random primer(s).

14. The method of claim 1, wherein said one or more primers hybridize to one or more adapter sequence.