Sets of genes have been described recently that are found only in genomes that contain CRISPR repeats, and almost always near the repeats themselves. Such CRISPR-associated genes are called cas genes. More than forty different Cas protein families have been described. The most important of these is Cas1, which is present in almost every CRISPR/Cas system. Particular combinations of cas genes are found together regularly, along with characteristic subclasses of CRISPR repeat and corresponding subfamilies of the Cas1 family. These combinations appear to represent distinct CRISPR/Cas subtypes; several different subtypes may occur in a single genome. The sporadic distribution of each CRISPR/cas subtype suggests that these elements undergo numerous horizontal gene transfer events during microbial evolution. In the bacteria E. coli the CasA-E proteins form a functional complex, Cascade, that process CRISPR RNA transcripts into spacer-repeat units that are retained by Cascade. CRISPR-based phage inactivation in E. coli requires Cascade and Cas3, but not Cas1 and Cas2.
The understanding of the mechanism of action of CRISPR systems has progressed very quickly in the past few years; it may indeed represent a prokaryotic analog of eukaryotic RNA interference systems that provides bacteria with a form of acquired immunity.
Prevalence of clustered regulatory interspaced short palindromic repeat (CRISPR)-like sequences in mitis-group streptococci
Apr 01, 2011; ABSTRACT Clustered regulatory interspaced short palindromic repeats (CRISPRs) have been discovered in many bacteria and...
Evolutionary conservation of sequence and secondary structures in CRISPR repeats.(Research)(clustered regularly interspaced short palindromic repeats)
Apr 18, 2007; Authors: Victor Kunin (corresponding author) (equal contributor) ; Rotem Sorek (equal contributor) ; Philip Hugenholtz...