title: Bacteriophage genes that inactivate the CRISPR/Cas bacterial immune system.
abstract: A widespread system used by bacteria for protection against potentially dangerous foreign DNA molecules consists of the clustered regularly interspaced short palindromic repeats (CRISPR) coupled with cas (CRISPR-associated) genes. Similar to RNA interference in eukaryotes, these CRISPR/Cas systems use small RNAs for sequence-specific detection and neutralization of invading genomes. Here we describe the first examples of genes that mediate the inhibition of a CRISPR/Cas system. Five distinct 'anti-CRISPR' genes were found in the genomes of bacteriophages infecting Pseudomonas aeruginosa. Mutation of the anti-CRISPR gene of a phage rendered it unable to infect bacteria with a functional CRISPR/Cas system, and the addition of the same gene to the genome of a CRISPR/Cas-targeted phage allowed it to evade the CRISPR/Cas system. Phage-encoded anti-CRISPR genes may represent a widespread mechanism for phages to overcome the highly prevalent CRISPR/Cas systems. The existence of anti-CRISPR genes presents new avenues for the elucidation of CRISPR/Cas functional mechanisms and provides new insight into the co-evolution of phages and bacteria.
authors.affiliation: Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5S 1A8, Canada.
authors.forename: Joe
authors.initials: J
authors.lastname: Bondy-Denomy
authors.forename: April
authors.initials: A
authors.lastname: Pawluk
authors.forename: Karen L
authors.initials: KL
authors.lastname: Maxwell
authors.forename: Alan R
authors.initials: AR
authors.lastname: Davidson
mesh_terms: D001435:Bacteriophages / Q000235:genetics*; D005075:Biological Evolution; D015967:Gene Expression Regulation, Viral; D005798:Genes, Bacterial / Q000235:genetics*; D005814:Genes, Viral / Q000235:genetics*; D016679:Genome, Viral / Q000235:genetics; D055029:Inverted Repeat Sequences / Q000235:genetics*; D008969:Molecular Sequence Data; D011550:Pseudomonas aeruginosa / Q000235:genetics / Q000276:immunology* / Q000821:virology*