Nucleobase editors and methods of use thereof

A system for base editing comprising:

• a first nucleotide sequence encoding a N-terminal portion of a Cas9 nickase fused at its C-terminus to an intein-N;
• and
• a second nucleotide sequence encoding an intein-C fused to the N-terminus of a C-terminal portion of the Cas9 nickase;
• wherein the first nucleotide sequence further comprises a nucleotide sequence encoding a nucleotide deaminase fused to the N-terminus of the N-terminal portion of the Cas9 nickase,
• wherein the Cas9 nickase comprises amino acid substitutions L1111R, D1135V, G1218R, A1322R, and T1337R with at least one additional amino acid substitution A262T, R324L, S409I, E480K, E543D, E1219V or M694I when compared to SEQ ID NO:
• 11.

A composition comprising:

• a first recombinant adeno-associated virus (AAV) particle comprising a first nucleotide sequence encoding a N-terminal portion of a Cas9 nickase fused at its C-terminus to an intein-N;
• and
• a second recombinant AAV particle comprising a second nucleotide sequence encoding an intein-C fused to the N-terminus of a C-terminal portion of the Cas9 nickase;
• wherein first nucleotide sequence further comprises a nucleotide sequence encoding a nucleotide deaminase fused to the N-terminus of the N-terminal portion of the Cas9 nickase,
• wherein the Cas9 nickase comprises amino acid substitutions L1111R, D1135V, G1218R, A1322R, and T1337R with at least one additional amino acid substitution A262T, R324L, S409I, E480K, E543D, E1219V or M694I when compared to SEQ ID NO:
• 11.