Some aspects of this disclosure provide strategies, systems, reagents, methods, and kits that are useful for the targeted editing of nucleic acids, including editing a
single site within the
genome of a
cell or subject, e.g., within the human
genome. The disclosure provides fusion proteins of
nucleic acid programmable
DNA binding proteins (napDNAbp), e.g., Cas9 or variants thereof, and
nucleic acid editing proteins such as
cytidine deaminase domains (e.g., novel
cytidine deaminases generated by ancestral
sequence reconstruction), and
adenosine deaminases that deaminate adenine in
DNA. Aspects of the disclosure relate to fusion proteins (e.g., base editors) that have improved expression and / or localize efficiently to the
nucleus. In some embodiments, base editors are
codon optimized for expression in mammalian cells. In some embodiments, base editors include multiple nuclear localization sequences (e.g., bipartite NLSs), e.g., at least two NLSs. In some embodiments, methods for targeted
nucleic acid editing are provided.