DBE2 is an artificial 'base editor' that can be used to to irreversibly convert a single target cytidine DNA base in a programmable manner, without requiring double-stranded cleavage of the DNA backbone or a donor template. DBE2 is a modified version of the mammalian-optimized BE2 base editor described in PMID:27096365; to optimize the base editor for use in Drosophila, the Cas9 sequence present in DBE2 contains four point mutations ('m4') instead of the two mutations ('m2) present in mammalian-optimized BE2 (FBrf0229805 previously showed that the m4 Cas9 variant functions more effectively than the m2 variant as a tether for targeting loci in Drosophila). DBE2 is composed of the rat Apobec1 cytidine deaminase ( RGDID:2133 ) fused, via a 16-residue XTEN linker, to a catalytically dead form of the Cas9 endonuclease from Streptococcus pyogenes (contains four amino acid substitutions: D10A, D839A, H840A and N863A), followed by the uracil DNA glycosylase inhibitor (UGI) from Bacillus subtilis bacteriophage PBS1. The Cas9 sequence allows DBE2 to be targeted to a genomic target site of interest in the presence of a guide RNA (gRNA), where the APOBEC1 enzyme mediates the conversion of cytidine (C) to uridine (the highest rate of conversion is found in positions 3-9 of the gRNA targeted site). During DNA repair or replication, the uridine residue has base-pairing properties of a thymine (T) residue. This results in a C-to-T change on the top strand, and a guanosine-to-adenosine (G-to-A) change if the gRNA targets the bottom strand (adapted from FBrf0252249).