Single-stranded DNA adenine bases (ABE8.8 editing window) (ssDNA adenine)

Single-stranded DNA adenine bases within the ABE8.8 editing window represent the specific chemical substrate for adenine base editors (ABEs). ABE8.8 is a high-activity CRISPR-based tool consisting of a laboratory-evolved TadA deaminase fused to a catalytically impaired Cas9 nickase (Richter et al., 2020, Nature Biotechnology). When the Cas9 complex binds to a specific genomic locus guided by an RNA sequence, it creates an R-loop structure, exposing a segment of the non-target DNA strand as single-stranded DNA (Lapinaite et al., 2020, Science). Within this defined editing window, the deaminase enzyme catalyzes the hydrolytic deamination of adenine to inosine (Gaudelli et al., 2017, Nature). Because inosine is biochemically read as guanine by DNA polymerases during replication or repair, this process effectively results in a permanent A•T to G•C base pair conversion. This target is central to the treatment of pathogenic point mutations, such as those found in sickle cell disease or certain forms of hereditary blindness, by enabling precise genomic correction without requiring double-strand breaks.

Other names

Adenine in R-loopABE8.8 substrateDeoxyadenosine substrateA•T to G•C editing siteNon-target strand adenine

Hydrolytic deamination of adenine to inosine within a CRISPR-induced R-loop, followed by DNA replication or repair that treats inosine as guanine, resulting in a permanent A•T to G•C transition.