Research Article

Crystal structure of the CRISPR RNA–guided surveillance complex from Escherichia coli

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Science  07 Aug 2014:
DOI: 10.1126/science.1256328

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Clustered regularly interspaced short palindromic repeats (CRISPRs) are essential components of RNA-guided adaptive immune systems that protect bacteria and archaea from viruses and plasmids. In Escherichia coli, short CRISPR-derived RNAs (crRNAs) assemble into a 405 kDa multi-subunit surveillance complex called Cascade (CRISPR-associated complex for antiviral defense). Here, we present the 3.24 Å resolution x-ray crystal structure of Cascade. Eleven proteins and a 61-nucleotide crRNA assemble into a sea-horse-shaped architecture that binds double-stranded DNA targets complementary to the crRNA-guide sequence. Conserved sequences on the 3′- and 5′-ends of the crRNA are anchored by proteins at opposite ends of the complex, while the guide sequence is displayed along a helical assembly of six interwoven subunits that present 5-nucleotide segments of the crRNA in pseudo A-form configuration. The structure of Cascade suggests a mechanism for assembly and provides insights into the mechanisms of target recognition.

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