CRISPR
CRISPR began as the immune memory of bacteria. When a virus attacks, a microbe can file away a short snippet of the invader's DNA, like keeping a mugshot. If that virus returns, the cell makes RNA copies of the stored snippet to recognize and destroy the matching viral DNA. Scientists realized this “search-and-cut” system could be reprogrammed to target almost any DNA we choose.
The acronym stands for Clustered Regularly Interspaced Short Palindromic Repeats — the repetitive DNA stretches, interrupted by stored invader sequences (spacers), found in bacterial genomes. Paired with a CRISPR-associated (Cas) protein such as Cas9, and given a custom guide RNA, the system becomes a programmable tool: tell it the 20-letter sequence you want, and it finds and cuts that site in a genome.
Because it is cheap, fast, and easy to redirect simply by changing the guide RNA, CRISPR transformed genome editing after 2012 and earned a 2020 Nobel Prize. It is not flawless — off-target cutting, delivery into cells, and unpredictable repair remain real challenges — and CRISPR is a family of systems, not a single molecule.
Researchers used CRISPR-Cas9 to disable a faulty gene in human cells by supplying a guide RNA matching the gene's sequence; Cas9 cut there, and error-prone repair scrambled the gene.
Reprogramming the bacterial defense system to edit a chosen gene.
In nature CRISPR is a bacterial defense; the editing tool is more precisely called the “CRISPR-Cas system.” Cas9 is the best known nuclease, but many Cas variants exist.