In prokaryotes such as bacteria, the CRISPR-Cas system can act as part of the immune system, targeting and degrading foreign DNA components in bacteria.
In an article published in Nature, scientists from the University of Würzburg, Germany, and other institutions have identified a nuclease, Cas12a2, from Sulfuricurvum sp. PC08-66.
It exhibits non-specific cleavage activity of double-stranded DNA, single-stranded DNA and single-stranded RNA after recognition of foreign plasmids guided by crRNA.
Activation of Cas12a2 induces an SOS response in bacteria and inhibits bacterial growth.
The cleavage activity of which on double-stranded DNA drives the bacteria into dormancy and death, leading to abortion of infection by foreign DNA.
In another study published in Nature, scientists from the University of Texas at Austin and other institutions determined the two-, three- and four-dimensional structure of Cas12a2, revealing its complete course of action.
It was shown that Cas12a2 is initially self-repressed and, when activated by the PFS sequence (protospacer-flanking sequence), is able to bind RNAs paired with its crRNA.
In addition, Cas12a2 binds and degrades double-stranded DNA by distorting it and promoting the lysis of some of its regions, and exerts an immune function.
The study shows that this first bacterium discovered so far relies on a single nuclease to recognize invaders and degrade the defense system of DNA and RNA within the bacterium.