Adenine bases in single-stranded DNA (ABE7.10 editing window) (ssDNA Adenine (ABE7.10))

Single-stranded DNA adenine bases within the ABE7.10 editing window are the specific molecular targets for Adenine Base Editors (ABEs), which are engineered tools designed for precise genome editing. ABE7.10 is a prominent variant composed of a nickase Cas9 (nCas9) fused to an evolved TadA deoxyadenosine deaminase domain (Gaudelli et al., Nature, 2017). When the CRISPR-Cas9 system targets a specific genomic sequence, it unwinds the DNA double helix, creating a single-stranded DNA loop known as an R-loop. Within a specific "window" of this loop—typically positions 4 through 7 or 8 of the protospacer—the adenine bases become accessible to the deaminase enzyme (Rees & Liu, Nature Reviews Genetics, 2018). The enzyme catalyzes the conversion of adenine to inosine, which the cell's machinery subsequently recognizes as guanine during DNA replication or repair, resulting in a permanent A•T to G•C base pair transition (Kantor et al., Chemical Reviews, 2020). This mechanism allows for the correction of pathogenic point mutations responsible for numerous genetic diseases without the need for double-strand breaks or donor DNA templates. However, the presence of multiple adenines within the window can lead to bystander editing, which remains a significant consideration in therapeutic design.

Other names

A•T to G•C editing siteDeoxyadenosine substrateABE7.10 target siteProtospacer adenine bases

Hydrolytic deamination of adenine to inosine within the single-stranded DNA bubble created by a CRISPR-Cas9 complex, followed by DNA replication or repair that treats inosine as guanine, resulting in an A-to-G transition.