CRISPR-Cas9 is a genetic technology that uses a guide RNA and the Cas9 enzyme to target and cut a chosen DNA sequence. The cell’s repair processes can then create a mutation or support a designed change.
The system originated from a bacterial defense mechanism against viruses. Bacteria store pieces of viral DNA in CRISPR arrays and use RNA molecules derived from those sequences to help recognize invading genetic material. Cas proteins perform the cutting step.
In 2012, researchers showed that CRISPR-Cas9 could be programmed to cut selected DNA targets in a laboratory system. The method rapidly became important in research, agriculture, and medical development because guide sequences can be redesigned relatively easily.
CRISPR-Cas9 is not the same as Sanger sequencing, which reads DNA, or RNA interference, which reduces gene expression using RNA. Cas9 cutting also requires a nearby protospacer-adjacent motif, commonly “NGG” for the widely used SpCas9 enzyme.