The G:U mismatch pair in cells is generally repaired by uracil DNA glycosylase (UNG)-mediated base excision repair (BER) process. Inhibition of UNG would protect the edited G:U intermediate from cleavage and thus improve C-to-T conversion efficiency and editing product purity (Fig. ). We fused two uracil glycosylase inhibitor (UGI) to the C terminus of dSt1Cas9 to create the C-to-T base editor (CTBEWT). To examine the C-to-T editing efficiency of CTBEWT, five CTBEWT plasmids targeting five different loci were separately electroporated into M. smegmatis.