Efficient C-to-G Base Editing with Improved Target Compatibility Using Engineered Deaminase-nCas9 Fusions

CRISPR-guided DNA base editors (BEs) are potent genome editing tools in biotechnology and medicine. However, conventional cytosine and adenine BEs can only induce base transitions (C-to-T and A-to-G) and cannot induce base transversions. Recently, several C-to-G base editors (CGBEs) were generated and applied in human cells. By comparing them, we found that engineered deaminases rather than additional base excision repair proteins significantly improved the C-to-G efficiency. In addition, significant increase in C-to-G transversions in the GC context were determined by using rationally engineered eAID deaminase. The genome-targeting scope of CGBEs were further expanded by using SpRY Cas9 variant, which then successfully induced stop codon (TAC to TAG) to disrupt gene in mouse embryos. Taken together, these new CGBEs with engineered deaminase-nCas9 fusions broaden the BE toolsets for efficient gene modification and therapeutic applications.