dCBE(ancBE4::Cas9(D10A)::NLS) is an artificial 'base editor' that can be used to irreversibly convert a single target cytosine DNA base in a programmable manner (using a guide RNA to direct the base editor to the target site), without requiring double-stranded cleavage of the DNA backbone or a donor template; it favors the conversion of C to T. dCBE(ancBE4::Cas9(D10A)::NLS) is composed of an optimized version of the APOBEC1 protein from Rattus norvegicus (ancestral sequence reconstruction 689, which contains 36 amino acid substitutions relative to the rat APOBEC1 sequence, see PMID:29813047) fused to the Cas9(D10A) nickase, with a Tag:NLS(SV40-largeT) nuclear localization signal at the C-terminal end of the fusion protein (FBrf0260443).