Evolution and classification of the CRISPR-Cas systems

K.S. Makarova, S.J.J. Brouns, J. van der Oost

Research output: Contribution to journalArticleAcademicpeer-review

1249 Citations (Scopus)


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
Original languageEnglish
Pages (from-to)467-477
JournalNature Reviews Microbiology
Issue number6
Publication statusPublished - 2011


  • provides acquired-resistance
  • dna-repair system
  • immune-system
  • small rna
  • repeats
  • prokaryotes
  • bacteria
  • defense
  • archaea
  • protein

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