Structure and activity of the RNA-targeting Type III-B CRISPR-Cas complex of Thermus thermophilus.


The CRISPR-Cas system is a prokaryotic host defense system against genetic elements. The Type III-B CRISPR-Cas system of the bacterium Thermus thermophilus, the TtCmr complex, is composed of six different protein subunits (Cmr1-6) and one crRNA with a stoichiometry of Cmr112131445361:crRNA1. The TtCmr complex copurifies with crRNA species of 40 and 46 nt, originating from a distinct subset of CRISPR loci and spacers. The TtCmr complex cleaves the target RNA at multiple sites with 6 nt intervals via a 5' ruler mechanism. Electron microscopy revealed that the structure of TtCmr resembles a "sea worm" and is composed of a Cmr2-3 heterodimer "tail," a helical backbone of Cmr4 subunits capped by Cmr5 subunits, and a curled "head" containing Cmr1 and Cmr6. Despite having a backbone of only four Cmr4 subunits and being both longer and narrower, the overall architecture of TtCmr resembles that of Type I Cascade complexes.

DOI: 10.1016/j.molcel.2013.09.013

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@article{Staals2013StructureAA, title={Structure and activity of the RNA-targeting Type III-B CRISPR-Cas complex of Thermus thermophilus.}, author={Raymond H J Staals and Yoshihiro Agari and Saori Maki-Yonekura and Yifan Zhu and David W Taylor and Esther van Duijn and Arjan Barendregt and Marnix Vlot and Jasper J Koehorst and Keiko Sakamoto and Akiko Masuda and Naoshi Dohmae and Peter J Schaap and Jennifer A Doudna and Albert J R Heck and Koji Yonekura and John van der Oost and Akeo Shinkai}, journal={Molecular cell}, year={2013}, volume={52 1}, pages={135-145} }