Programmable deaminase-free base editors for G-to-Y conversion by engineered glycosylase

Abstract Current DNA base editors contain nuclease and deaminase that enables deamination of cytosine (C) or adenine (A), but no method for guanine (G) thymine (T) editing is available now. Here we developed a deaminase-free glycosylase-based editor (gGBE) with G ability, by fusing Cas9 nickase engineered N-methylpurine glycosylase protein (MPG). By several rounds MPG mutagenesis via unbiased rational screening using an intron-split EGFP reporter, demonstrated gGBE could increase efficiency more than 1,500 folds. Furthermore, this exhibited high (up to 81.2%) G-to-T G-to-C (i.e., G-to-Y) conversion ratio 0.95) in both cultured human cells mouse embryos. Thus, have provided proof-of-concept new base-editing approach endowing the capability selectively excising type substrate.