In defense of phage: viral suppressors of CRISPR-mediated adaptive immunity in bacteria. (1/73)

Viruses that infect bacteria are the most abundant biological agents on the planet and bacteria have evolved diverse defense mechanisms to combat these genetic parasites. One of these bacterial defense systems relies on a repetitive locus, referred to as a CRISPR (clusters of regularly interspaced short palindromic repeats). Bacteria and archaea acquire resistance to invading viruses and plasmids by integrating short fragments of foreign nucleic acids at one end of the CRISPR locus. CRISPR loci are transcribed and the long primary CRISPR transcript is processed into a library of small RNAs that guide the immune system to invading nucleic acids, which are subsequently degraded by dedicated nucleases. However, the development of CRISPR-mediated immune systems has not eradicated phages, suggesting that viruses have evolved mechanisms to subvert CRISPR-mediated protection. Recently, Bondy-Denomy and colleagues discovered several phage-encoded anti-CRISPR proteins that offer new insight into the ongoing molecular arms race between viral parasites and the immune systems of their hosts.  (+info)

Comparative analysis ofCas6b processing and CRISPR RNA stability. (2/73)

The prokaryotic antiviral defense systems CRISP R (clustered regularly interspaced short palindromic repeats)/Cas (CRISP Rassociated) employs short crRNAs (CRISP R RNAs) to target invading viral nucleic acids. A short spacer sequence of these crRNAs can be derived from a viral genome and recognizes a reoccurring attack of a virus via base complementarity. We analyzed the effect of spacer sequences on the maturation of crRNAs of the subtype I-B Methanococcus maripaludis C5 CRISP R cluster. The responsible endonuclease, termed Cas6b, bound non-hydrolyzable repeat RNA as a dimer and mature crRNA as a monomer. Comparative analysis of Cas6b processing of individual spacer-repeat-spacer RNA substrates and crRNA stability revealed the potential influence of spacer sequence and length on these parameters. Correlation of these observations with the variable abundance of crRNAs visualized by deep-sequencing analyses is discussed. Finally, insertion of spacer and repeat sequences with archaeal poly-T termination signals is suggested to be prevented in archaeal CRISP R/Cas systems.  (+info)

Protospacer recognition motifs: mixed identities and functional diversity. (3/73)

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Diversity of CRISPR systems in the euryarchaeal Pyrococcales. (4/73)

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Holding a grudge: persisting anti-phage CRISPR immunity in multiple human gut microbiomes. (5/73)

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CRISPR-Cas: evolution of an RNA-based adaptive immunity system in prokaryotes. (6/73)

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Probabilistic models for CRISPR spacer content evolution. (7/73)

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CRISPR-spacer integration reporter plasmids reveal distinct genuine acquisition specificities among CRISPR-Cas I-E variants of Escherichia coli. (8/73)

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