Adenine DNA base editor variants with reduced off-target RNA editing

1. An adenine base editor (ABE) variant capable of deaminating adenine in DNA comprising an adenosine deaminase and a programmable DNA binding domain, wherein the adenosine deaminase comprises one or more Escherichia coli TadA monomers, wherein each E. coli TadA monomer has at least 90% sequence identity to the amino acid sequence of SEQ ID NO: 1 or the amino acid sequence of SEQ ID NO: 34, and wherein at least one of the one or more E. coli TadA monomers comprise one or more mutations at amino acid residue positions that correspond to amino acid residues 10, 11, 13, 21, 25, 26, 49, 58, 71, 72, 74, 77, 82, 109, 111, 122, 128, 129, 139, 140, 143, 148, 150, or 153 of the amino acid sequence of SEQ ID NO: 1 or the amino acid sequence of SEQ ID NO: 34.

2. The ABE variant of claim 1 , wherein the one or more mutations comprise mutations at amino acid residue positions that correspond to amino acid residues 11A, 13A, 20A, 21A, 25A, 26A, 49A, 58G, 71A, 72A, 74A, 77A, 82G, 109G, 109W, 111A, 122A, 128A, 129A, 139A, 140A, 143G, 148A, 150A, and/or 153A of the amino acid sequence of SEQ ID NO: 1 or the amino acid sequence of SEQ ID NO: 34.

3. The ABE variant of claim 2 , wherein the at least one of the one or more E. coli TadA monomers comprise mutations at amino acid residue positions that correspond to amino acid residues:

R13A;

20A and 21A;

21A, and 23A;

26A;

49A;

74A;

77A;

82G;

11A;

109W;

111A;

139A and 140A;

143G;

153A;

58G;

72A;

128A and 129A;

139A and 140A;

148A; or

150A

of the amino acid sequence of SEQ ID NO: 1 or the amino acid sequence of SEQ ID NO: 34.

4. The ABE variant of claim 1 , further comprising one or more nuclear localization sequences (NLS).

5. The ABE variant of claim 1 , further comprising a linker between the adenosine deaminase monomers and/or between the adenosine deaminase monomer or between a single-chain dimer and the programmable DNA binding domain.

6. The ABE variant of claim 1 , wherein the programmable DNA binding domain is an engineered C2H2 zinc-finger, a transcription activator effector-like effector (TALE), or a Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) Cas RNA-guided nucleases (CRISPR-Cas nuclease).

7. The ABE variant of claim 6 , wherein the CRISPR-Cas nuclease is a single strand DNA (ssDNA) nickase or is a catalytically inactive CRISPR-Cas nuclease.

8. The ABE variant of claim 7 , wherein the CRISPR-Cas nuclease is a Cas9 or Cas12a that has ssDNA nickase activity or is a catalytically inactive Cas9 or Cas12a.

9. A base editing system comprising:

(i) the ABE variant of claim 1 , wherein the programmable DNA binding domain is a CRISPR-Cas RNA guided nuclease (RGN); and

(ii) at least one guide RNA compatible with the base editing system that directs the base editing system to a target sequence.

10. A method of deaminating a selected adenine in a nucleic acid, the method comprising contacting the nucleic acid with the ABE variant of claim 1 , and at least one guide RNA compatible with the ABE variant that directs the ABE variant to a target sequence comprising the selected adenine.

11. The method of claim 10 , wherein the nucleic acid is in a cell.

12. The method of claim 11 , wherein the cell is in a living subject.

13. The method of claim 12 , wherein the living subject is a mammal.

14. A composition comprising the ABE variant of claim 1 , and at least one guide RNA compatible with the ABE variant that directs the ABE variant to a target sequence.

15. The composition of claim 14 , further comprising one or more ribonucleoprotein (RNP) complexes.

16. The ABE variant of claim 1 , wherein the at least one of the one or more E. coli TadA monomers comprise mutations at amino acid residue positions that correspond to amino acid residues 11A, and/or 139A/140A of the amino acid sequence of SEQ ID NO: 1 or the amino acid sequence of SEQ ID NO: 34.

17. The ABE variant of claim 1 , wherein the at least one of the one or more E. coli TadA monomers comprise mutations that correspond to 58G, 72A, 128A/129A, 139A/140A, 148A, and 150A of the amino acid sequence of SEQ ID NO: 1 or the amino acid sequence of SEQ ID NO: 34.

18. The ABE variant of claim 1 , wherein each E. coli TadA monomer has at least 95% sequence identity to the amino acid sequence of SEQ ID NO: 1 or the amino acid sequence of SEQ ID NO: 34.

19. The ABE variant of claim 1 , wherein each E. coli TadA monomer has at least 98% sequence identity to the amino acid sequence of SEQ ID NO: 1 or the amino acid sequence of SEQ ID NO: 34.