Genomic DNA at sgRNA-programmed adenine sites (ABE target site)

Genomic DNA at sgRNA-programmed adenine sites refers to the specific chromosomal locations targeted by adenine base editors (ABEs) for therapeutic modification. These sites are identified by a single-guide RNA (sgRNA) that directs a fusion protein—consisting of a catalytically impaired Cas9 (nCas9) and an engineered adenine deaminase enzyme, such as TadA—to a complementary DNA sequence (Gaudelli et al., 2017). The biological function of these sites is to serve as the template for genetic inheritance and protein synthesis, which can be altered to correct deleterious mutations. Upon binding, the ABE converts a specific adenine (A) to inosine (I), which is subsequently read as guanine (G) by DNA polymerases, resulting in a permanent A•T to G•C transition (Kantor et al., 2020). This mechanism is particularly valuable for treating genetic diseases caused by point mutations, such as sickle cell disease or alpha-1 antitrypsin deficiency, where a single base change can restore normal protein function (Beam Therapeutics, 2024). Unlike traditional CRISPR-Cas9, targeting these sites does not involve double-strand breaks, significantly reducing the risk of uncontrolled insertions, deletions, or chromosomal translocations. Therapeutic agents like BEAM-101 and BEAM-302 are currently in clinical and preclinical development to target these sites in specific genes to treat life-threatening conditions (Newby & Liu, 2021). Monitoring efficacy at these sites typically involves high-throughput sequencing to quantify the percentage of successful base conversion and assess potential off-target effects.

Other names

Adenine base editor targetCRISPR-Cas9 adenine target siteGenomic A-T target sitesgRNA-directed adenine site

Adenine deamination to inosine by an engineered deaminase (e.g., TadA) fused to a CRISPR-Cas9 nickase, leading to a permanent A•T to G•C base pair transition during DNA replication or repair.