Figure 4.

The mechanisms of base editing. In the absence of double-strand breaks (DSBs), base editing facilitates the introduction of precise point mutations at specified target sites in the genome via nucleotide substitution. (A) Cytidine deaminase base editing (CBE) is performed in conjunction with the use of an APOBEC1 cytidine deaminase, which converts C to U. Subsequently the U-G mismatch is resolved via cellular mismatch repair or base editing mismatch repair machinery that leads to the formation of T-A at the target locus. (B) The adenine base editing (ABE) leads A-T to G-C substitution. After recruiting to the targeted genomic locus, the ABE delaminates targeted A base to I (inosine) leading to I-T base pairing. The cellular mismatch repair mechanism or DNA replication resolves the I-T, forming G-C base pairing.