Journal
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
Volume 108, Issue 25, Pages 10092-10097Publisher
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1102716108
Keywords
Cmr; RNA interface; RNA silencing; Argonaute; surveillance system
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Funding
- National Science Foundation
- Bill and Melinda Gates Foundation
- Veni grant [700.58.402]
- Netherlands Proteomics Centre
- Netherlands Organisation for Scientific Research
- Engineering and Physical Science Research Council
- Biotechnology and Biological Sciences Research Council
- Engineering and Physical Sciences Research Council [EP/D033713/1, EP/E036252/1] Funding Source: researchfish
- EPSRC [EP/E036252/1, EP/D033713/1] Funding Source: UKRI
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Prokaryotes have evolved multiple versions of an RNA-guided adaptive immune system that targets foreign nucleic acids. In each case, transcripts derived from clustered regularly interspaced short palindromic repeats (CRISPRs) are thought to selectively target invading phage and plasmids in a sequence-specific process involving a variable cassette of CRISPR-associated (cas) genes. The CRISPR locus in Pseudomonas aeruginosa (PA14) includes four cas genes that are unique to and conserved in microorganisms harboring the Csy-type (CRISPR system yersinia) immune system. Here we show that the Csy proteins (Csy1-4) assemble into a 350 kDa ribonucleoprotein complex that facilitates target recognition by enhancing sequence-specific hybridization between the CRISPR RNA and complementary target sequences. Target recognition is enthalpically driven and localized to a seed sequence at the 5' end of the CRISPR RNA spacer. Structural analysis of the complex by small-angle X-ray scattering and single particle electron microscopy reveals a crescent-shaped particle that bears striking resemblance to the architecture of a large CRISPR-associated complex from Escherichia coli, termed Cascade. Although similarity between these two complexes is not evident at the sequence level, their unequal subunit stoichiometry and quaternary architecture reveal conserved structural features that may be common among diverse CRISPR-mediated defense systems.
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