CRISPR

CRISPR is a term in DNA research. It stands for "clustered regularly-interspaced short palindromic repeats". These are part of the genetic code in prokaryotes: most bacteria and archaea have it. It is their defence against attack by viruses. Its structure and function was discovered in the 21st century.
CRISPR has a lot of short repeated sequences. These sequences are part of an adaptive immune system for prokaryotes. It allows them to remember and counter the bacteriophages which prey on them. They work as a kind of acquired immunity for bacteria.
They can modify the genes of almost any organism. They are used by researchers as a tool to cut and insert genes in genetic modification (GM). Work is under way to find how they can be used to attack virus diseases in humans (gene therapy).
How it works.
Each repetition is followed by short segments of "spacer DNA". These come from previous exposures to a bacterial virus or plasmid. CRISPR spacers "recognize and cut up the foreign genetic elements" in a manner like RNA interference in eukaryotic organisms.
In effect, the spacers are fragments of DNA from viruses that have previously tried to attack the cell line. The foreign source of the spacers was a sign to researchers that the CRISPR/cas system could have a role in adaptive immunity in bacteria.
The actual cutting is done by a nuclease called Cas9. "Cas9" has two active cutting sites, one for each strand of the DNA's double helix. "Cas9" does this by unwinding foreign DNA and checking whether it is complementary to the 20 basepair spacer region of the guide RNA (the spacer region RNA). If it is, the foreign DNA gets chopped up.
Applications.
CRISPR is an anti-viral defensive system which originated in bacteria and archaea. Gene editing is a human exploitation of CRISPR.
The technology has been used to switch off genes in human cell lines and cells, to study "Candida albicans", to modify yeasts used to make biofuel and to genetically modify crop strains.
The CRISPR-Cas9 system cuts DNA, but can do more. It can turn gene expression on and off, and can be used to fluorescently tag particular sequences.
Nobel award.
The understanding and development of the CRISPR-Cas9 genome editing technique won the Nobel Prize in Chemistry for 2020. The prize was awarded jointly to Emmanuelle Charpentier and Jennifer Doudna.