Genomic DNA cytosine (at a guide RNA-programmed locus) (Target C)

Genomic DNA cytosine at the intended guide RNA-programmed locus refers to the specific nucleotide substrate targeted by cytosine base editors (CBEs) for precise genetic modification (Komor et al., 2016, Nature). In this system, a catalytically impaired Cas9 protein (nCas9) is guided by a specific RNA sequence to a genomic site, where it unwinds the DNA to create a single-stranded 'bubble' (Rees & Liu, 2018, Nature Reviews Genetics). A deaminase enzyme fused to the Cas9 then converts the target cytosine into uracil through hydrolytic deamination. Because uracil is read as thymine by DNA polymerases, the cellular repair machinery or subsequent rounds of replication result in a permanent C-to-T (or G-to-A on the opposite strand) transition (Gaudelli et al., 2017, Nature). This technology is used to correct pathogenic point mutations or to introduce premature stop codons to silence disease-associated genes, such as PCSK9 in cardiovascular disease (Musunuru et al., 2021, Nature). The target is distinct from traditional protein targets as it involves the direct chemical modification of the genome itself. Safety considerations primarily involve off-target effects at non-intended genomic locations and 'bystander' editing of adjacent cytosines within the activity window (Kim et al., 2019, Nature Biotechnology). Clinical applications, such as VERVE-101, demonstrate the potential of targeting specific genomic cytosines to treat chronic conditions (Verve Therapeutics, 2023).

Other names

Target cytosineProtospacer cytosineSubstrate cytosineGenomic CTargeted cytidine

Targeted hydrolytic deamination of cytosine to uracil within a single-stranded DNA bubble, followed by DNA repair or replication to achieve a permanent C-to-T transition (Komor et al., 2016, Nature).