CRISPR

CRISPR stands for clustered regularly interspaced short palindromic repeats, stretches of repeated DNA found in many bacteria and archaea. Between the repeats sit short spacers, pieces of DNA captured from viruses that attacked the cell or its ancestors. The cell copies these into RNA guides that, together with CRISPR-associated (Cas) enzymes, recognize and cut the matching viral DNA if the virus returns, making CRISPR a kind of adaptive immune system for microbes.

Researchers turned this system into a tool for editing genes; Emmanuelle Charpentier and Jennifer Doudna described the approach in 2012 and shared the 2020 Nobel Prize in Chemistry for it. In the most widely used version, scientists design a single guide RNA whose sequence matches the target site and pair it with the Cas9 enzyme. Cas9 cuts both strands of the DNA there, next to a short sequence called a PAM. The cell then repairs the break, either by rejoining the ends, which often disables the gene, or by copying a supplied DNA template, which can insert or correct a sequence.

Because it is cheaper, faster and more precise than older methods, CRISPR is used across research, agriculture and medicine, including a first approved therapy for sickle cell disease. Editing embryos and other inheritable cells remains highly controversial.