RNA Targeting by the Type III-A CRISPR-Cas Csm Complex of Thermus thermophilus
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Publication date
2014-11-20
Authors
Staals, Raymond H J
Zhu, Yifan
Taylor, David W
Kornfeld, Jack E
Sharma, Kundan
Barendregt, Arjan
Koehorst, Jasper J
Vlot, Marnix
Neupane, Nirajan
Varossieau, Koen
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Abstract
CRISPR-Cas is a prokaryotic adaptive immune system that provides sequence-specific defense against foreign nucleic acids. Here we report the structure and function of the effector complex of the Type III-A CRISPR-Cas system of Thermus thermophilus: the Csm complex (TtCsm). TtCsm is composed of five different protein subunits (Csm1-Csm5) with an uneven stoichiometry and a single crRNA of variable size (35-53 nt). The TtCsm crRNA content is similar to the Type III-B Cmr complex, indicating that crRNAs are shared among different subtypes. A negative stain EM structure of the TtCsm complex exhibits the characteristic architecture of Type I and Type III CRISPR-associated ribonucleoprotein complexes. crRNA-protein crosslinking studies show extensive contacts between the Csm3 backbone and the bound crRNA. We show that, like TtCmr, TtCsm cleaves complementary target RNAs at multiple sites. Unlike Type I complexes, interference by TtCsm does not proceed via initial base pairing by a seed sequence.
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Staals, R H J, Zhu, Y, Taylor, D W, Kornfeld, J E, Sharma, K, Barendregt, A, Koehorst, J J, Vlot, M, Neupane, N, Varossieau, K, Sakamoto, K, Suzuki, T, Dohmae, N, Yokoyama, S, Schaap, P J, Urlaub, H, Heck, A J R, Nogales, E, Doudna, J A, Shinkai, A & van der Oost, J 2014, 'RNA Targeting by the Type III-A CRISPR-Cas Csm Complex of Thermus thermophilus', Molecular Cell, vol. 56, no. 4, pp. 518-30. https://doi.org/10.1016/j.molcel.2014.10.005