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Mol Cell. 2014 Nov 20;56(4):506-17. doi: 10.1016/j.molcel.2014.09.027. Epub 2014 Nov 6.

Programmable RNA shredding by the type III-A CRISPR-Cas system of Streptococcus thermophilus.

Author information

1
Department of Protein-DNA Interactions, Institute of Biotechnology, Vilnius University, Graiciuno 8, Vilnius 02241, Lithuania.
2
Department of Bioinformatics, Institute of Biotechnology, Vilnius University, Graiciuno 8, Vilnius 02241, Lithuania.
3
Department of Chemical and Biological Engineering, ChELSI Institute, University of Sheffield, Mappin Street, Sheffield S1 3JD, UK.
4
DuPont Nutrition and Health, BP10, Dangé-Saint-Romain 86220, France.
5
Department of Protein-DNA Interactions, Institute of Biotechnology, Vilnius University, Graiciuno 8, Vilnius 02241, Lithuania. Electronic address: siksnys@ibt.lt.

Abstract

Immunity against viruses and plasmids provided by CRISPR-Cas systems relies on a ribonucleoprotein effector complex that triggers the degradation of invasive nucleic acids (NA). Effector complexes of type I (Cascade) and II (Cas9-dual RNA) target foreign DNA. Intriguingly, the genetic evidence suggests that the type III-A Csm complex targets DNA, whereas biochemical data show that the type III-B Cmr complex cleaves RNA. Here we aimed to investigate NA specificity and mechanism of CRISPR interference for the Streptococcus thermophilus Csm (III-A) complex (StCsm). When expressed in Escherichia coli, two complexes of different stoichiometry copurified with 40 and 72 nt crRNA species, respectively. Both complexes targeted RNA and generated multiple cuts at 6 nt intervals. The Csm3 protein, present in multiple copies in both Csm complexes, acts as endoribonuclease. In the heterologous E. coli host, StCsm restricts MS2 RNA phage in a Csm3 nuclease-dependent manner. Thus, our results demonstrate that the type III-A StCsm complex guided by crRNA targets RNA and not DNA.

PMID:
25458845
DOI:
10.1016/j.molcel.2014.09.027
[Indexed for MEDLINE]
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