CRISPR

CRISPR stands for clustered regularly interspaced short palindromic repeats. In bacteria and archaea, CRISPR-Cas systems provide adaptive immunity by storing short DNA fragments from invaders as spacers, which guide Cas nucleases to recognize and cut matching sequences. The term also refers to the associated Cas proteins that perform the nuclease activity. The most widely used enzyme in genome editing is Cas9, derived from Streptococcus pyogenes.

In bacteria, adaptation, expression, and interference stages integrate new spacers, generate crRNA, and target invading DNA next to a PAM sequence. In genome editing, scientists harness a programmable nuclease such as Cas9 guided by a synthetic RNA to introduce a double-strand break at a chosen genomic site. The break is repaired by non-homologous end joining or homology-directed repair, enabling gene disruption or precise edits.

CRISPR tools enable basic research, functional genomics, and potential therapies. Applications include gene knockout, insertion, or replacement in model organisms and cells; crop improvement; and diagnostic methods such as SHERLOCK and DETECTR. Newer derivatives expand capabilities to edit bases without breaks (base editors) or perform precise edits without double-strand breaks (prime editing).

Limitations include off-target edits, mosaicism, and dependence on PAM sequences; delivery to cells and tissues remains challenging. Ethical and regulatory considerations concern human germline editing, equity of access, and ecological impact.

CRISPR was first observed as a bacterial genome feature in the 1980s and 1990s, and its function as an immune system was established in the 2000s. In 2012–2013, Jennifer Doudna and Emmanuelle Charpentier demonstrated that CRISPR-Cas9 could be directed by RNA to edit genomes, leading to rapid adoption and ongoing development of CRISPR-based technologies.