CRISPR/Cas is a bacterial adaptive immune mechanism against viral and plasmid invaders, repurposed as a genome-editing tool: a guide RNA (a fusion of a target-specific crRNA and a scaffold tracrRNA) directs the Cas9 nuclease to a genomic sequence complementary to the guide and adjacent to a short protospacer-adjacent motif (PAM), where Cas9 introduces a site-specific double-strand break. The resulting break is resolved by one of two DNA repair pathways—non-homologous end joining, which introduces random insertions/deletions and produces gene disruption without a donor template, or homology-directed repair, which uses a donor template to integrate specific sequence changes such as point mutations, insertions, deletions, or reporter tags. This places CRISPR/Cas9 within the domain of molecular biology and genome engineering, contrasted with earlier protein-guided editing systems (zinc-finger nucleases and TALENs) that rely on engineered DNA-binding protein domains rather than RNA-guided targeting.
CRISPR/Cas is a bacterial adaptive immune mechanism against viral and plasmid invaders, repurposed as a genome-editing tool: a guide RNA (a fusion of a target-specific crRNA and a scaffold tracrRNA) …