comment by morganism ·
2017-01-13T20:11:11.335Z · LW(p) · GW(p)
"Whatever other functions CRISPR–Cas has, it is clear that some microbes use it more than others. More than 90% of archaea have CRISPR-based immunity, whereas only about one-third of sequenced bacteria bother with it, says Koonin. And no non-prokaryotic organisms, even single-celled ones, have been caught troubling with CRISPR–Cas at all.
"In some bacteria, CRISPR–Cas components control DNA repair, gene expression and the formation of biofilms. They can also determine a bacterium's ability to infect others: Legionella pneumophila, which causes Legionnaires' disease, must have the Cas protein Cas2 in order to infect the amoeba that is its natural host. “A major question is how much biology is there that goes beyond defence,”
"Researchers have officially recognized 6 different types of CRISPR system, with 19 subtypes. “And we really only know how a fraction of them actually work,” says Marraffini.
Unravelling those mechanisms could hold the key to finding new biotechnological applications for CRISPR–Cas systems. The beloved CRISPR–Cas9, for example, is a type II system, which uses RNA molecules transcribed from spacer sequences to direct an enzyme to cut invading viral or plasmid DNA. But enzymes in type VI systems — discovered last year6 — cut up RNA rather than DNA. And type IV systems contain some genes associated with CRISPR–Cas, but lack the repeats and the machinery to insert spacers."