CRISPR genome editing relies on Cas9 (or related Cas nucleases) being guided by an RNA sequence to a specific genomic site, where it introduces a double-strand break that the cell repairs either through error-prone non-homologous end joining (producing insertions/deletions, i.e., gene knockout) or, in the presence of a donor DNA template, through homology-directed repair (enabling precise sequence insertion, i.e., knock-in). Because Cas9 protein and guide RNA must be delivered intact into a cell — crossing the membrane, escaping the endosome, and reaching the cytosol or nucleus — the CRISPR machinery can be introduced in different molecular formats (plasmid DNA, mRNA, or pre-formed ribonucleoprotein complex), each with distinct tradeoffs in expression kinetics, persistence, and off-target activity, situating this within molecular biology's broader domain of intracellular macromolecule delivery (transfection).
CRISPR genome editing relies on Cas9 (or related Cas nucleases) being guided by an RNA sequence to a specific genomic site, where it introduces a double-strand break that the cell repairs either thro…