Evolution and classification of the CRISPR-Cas systems.

Makarova, Kira S.; Haft, Daniel H.; Barrangou, Rodolphe; Brouns, Stan J. J.; Charpentier, Emmanuelle; Horvath, Philippe; Moineau, Sylvain; Mojica, Francisco J. M.; Wolf, Yuri I.; Yakunin, Alexander F.; van der Oost, John; Koonin, Eugene V.

The CRISPR-Cas (clustered regularly interspaced short palindromic repeats-CRISPR-associated proteins) modules are adaptive immunity systems that are present in many archaea and bacteria. These defence systems are encoded by operons that have an extraordinarily diverse architecture and a high rate of evolution for both the cas genes and the unique spacer content. Here, we provide an updated analysis of the evolutionary relationships between CRISPR-Cas systems and Cas proteins. Three major types of CRISPR-Cas system are delineated, with a further division into several subtypes and a few chimeric variants. Given the complexity of the genomic architectures and the extremely dynamic evolution of the CRISPR-Cas systems, a unified classification of these systems should be based on multiple criteria. Accordingly, we propose a 'polythetic' classification that integrates the phylogenies of the most common cas genes, the sequence and organization of the CRISPR repeats and the architecture of the CRISPR-cas loci.

IMMUNITY; ARCHAEBACTERIA; OPERONS; BACTERIAL evolution; BIOLOGICAL evolution; GENETICS; NUCLEOTIDE sequence

Nature Reviews Microbiology, 2011, Vol 9, Issue 6, p467

1740-1526

Academic Journal

10.1038/nrmicro2577