CRISPR--a widespread system that provides acquired resistance against phages in bacteria and archaea.

CRISPR – a widespread system that provides acquired resistance against phages in bacteria and archaea Rotem Sorek*, Victor Kunin and Philip Hugenholtz Joint Genome Institute, 2800 Mitchell Drive, Walnut Creek, CA 94598 * Corresponding author: rsorek@lbl.gov Abstract Arrays of clustered, regularly spaced short palindromic repeats (CRISPR) are widespread in the genomes of many bacteria and almost all archaea. These arrays are composed of direct repeats sized 24-47 bp separated by similarly sized non-repetitive sequences (spacers). It was recently experimentally shown that CRISPR arrays, along with a group of associated proteins, confer resistance to phage. Following exposure to phage, bacteria integrate new spacer sequences that are derived from the phage genome. Acquisition of these spacers enables the bacterial cell to shutdown the phage attack, presumably by an RNA-interference-like mechanism. This Progress discusses the structure and function of CRISPRs and the implications of this new antiviral mechanism in bacteria.