Table 1.

List of base editors, characteristics, catalytic window and functions

Base editors	Characteristics	Type of base substitutions	Catalytic window	References
DNA base editors
BE1	(APOBEC1–XTEN–dCas9): Composed of a cytidine deaminase enzyme APOBEC1 (from rats) linked to a catalytically dead Cas9 (dcas9) by a 16 amino acid XTEN linker	C to T	−17 to −13	Komor et al. (2016)
BE2	(APOBEC–XTEN–dCas9–UGI): UGI is fused to the C terminus of BE1.	C to T	−17 to −13	Komor et al. (2016)
BE3	(APOBEC–XTEN–Cas9n–GI): rAPOBEC1 fused to the N terminus of nickase cas9 D10A through a 16‐amino acid XTEN linker and a UGI fused to the C terminus by a 4‐amino acid linker	C to T	−16 to −12	Komor et al. (2016)
YEE‐BE3	(W90Y+R126E+R132E): triple mutant	C to T	−15 to −13	Kim et al. (2017)
BE4	Composed of rAPOBEC1 fused to Cas9D10A through a 32‐aa linker and two UGI molecules are linked to both C and N terminal of Cas9 nickase by a 9‐aa linker.	C to T	−17 to −13	Komor et al. (2017)
SaBE4‐GAM	Gam protein fused to Staphylococcus aureus Cas9‐derived BE4	C to T	−19 to −9	Komor et al. (2017)
Target‐AID	Composed of nickase Cas9D10A and a cytidine deaminase pmCDA1 (from sea lamprey)	C to T	−19 to −15	Nishida et al. (2016)
TAM	dCas9 is fused to human AID; co‐expressed with UGI	C to T	−16 to −12	Ma et al. (2016)
CRISPR‐X	dCas9 is used to target a hyperactive AID variant to induce localized, diverse point mutations. The sgRNA backbone contains two MS2 RNA hairpins that each recruit two MS2 proteins fused to AID	C to T	−50 to +50	Hess et al. (2016)
ABE	TadA is fused to a catalytically impaired CRISPR/Cas9 mutant	A to G	−17 to −14	Gaudelli et al. (2017)
RNA base editor
ADAR	Catalytically inactive Cas13 (dCas13) is fused to a naturally occurring ADAR (adenosine deaminase acting on RNA)	A to 1	−50 to +50	Cox et al. (2017)