In prokaryotes, CRISPR–Cas adaptive immune systems target mobile genetic elements, including transposons, for nucleolytic degradation using Cas proteins and CRISPR RNA (crRNA) guides. However, several nuclease-deficient type I-F, I-B and V-K CRISPR–Cas systems have been co-opted by Tn7-like transposons to direct transposon DNA insertion into specific target sites. In these systems, DNA targeting involves transposon-encoded Cas effectors, either a multisubunit complexlacking Cas3 (termed Cascade) in type I systems or a single catalytically inactive Cas12k protein in type V-K systems, and results in transposon insertion at a fixed distance from the target site specified by the crRNA. Cas12k-mediated DNA targeting requires a crRNA guide and a trans-activating CRISPR RNA (tracrRNA), and is coupled to the concerted activities of three transposon proteins—the transposase TnsB, the AAA+ ATPase TnsC and the zinc-finger protein TniQ to direct transposon insertion downstream of the target site. Here you can see a recent structure of the Cas12k enzyme (yellow ribbons) in complex with the guide RNA (light blue ribbon) and a short DNA target fragment (blue spheres) determined by cryoEM (PDB code: 7PLA)
#molecularart ... #immolecular .. #CRISPR ... #transposon ... #cas12k ... #complex ... #guideRNA ... #targetDNA ... #crypto
Cas12k-gRNA-DNA complex rendered with @proteinimaging and represented with @corelphotopaint
#molecularart ... #immolecular .. #CRISPR ... #transposon ... #cas12k ... #complex ... #guideRNA ... #targetDNA ... #crypto
Cas12k-gRNA-DNA complex rendered with @proteinimaging and represented with @corelphotopaint
