Structure of an RNA Silencing Complex of the CRISPR-Cas Immune System (original) (raw)

“…Type II CRISPR systems are characterized by Cas9, a multidomain protein with a bilobed architecture harboring two nuclease sites that together catalyze cleavage of invading DNA (12, 21-24). The Csm system in CRISPR type IIIA and a related Cmr complex in type IIIB cleave DNA and RNA, respectively, forming a helical structure around crRNA that is structurally similar to Cascade (14,17,18,25,26).Whereas Cas9 and Csm/Cmr effector complexes directly recognize and nucleolytically degrade invading genes (12, 14, 16, 17, 21), Cascade complex by itself is not a nuclease for degradation of invader DNA (13). In Escherichia coli K-12 (type IE), Cascade recognizes and binds crRNA to complimentary sequence in target DNA, generating an RNA mediated displacement loop (R-loop) of single-stranded (ss) DNA and RNA-DNA hybrid within double-stranded (ds) target DNA (13).…”