CRISPR-based immunity in prokaryotes

Article By:

Westra, Edze R. Department of Agrotechnology and Food Sciences, Laboratory of Microbiology, Wageningen University, The Netherlands.

van der Oost, John Department of Agrotechnology and Food Sciences, Laboratory of Microbiology, Wageningen University, The Netherlands.

Brouns, Stan J. J. Department of Agrotechnology and Food Sciences, Laboratory of Microbiology, Wageningen University, The Netherlands.

Last reviewed:2011

DOI:https://doi.org/10.1036/1097-8542.YB110022

Recurrent viral attacks on prokaryotes have been a driving force for the evolution of immune mechanisms in these organisms that are crucial for their survival in the presence of these infectious elements. Viruses abuse bacteria to multiply, which often results in the death of the microbe. Therefore, bacteria have devised multiple defense strategies to resist phage predation. A relatively simple one is based on the elimination or modification of host proteins that are used by the virus as a surface receptor. Although this strategy prevents virus absorption and injection of the viral DNA, it may lead to an impaired fitness of the microbe. A second line of defense is formed by the well-studied restriction-modification system, which consists of an endonuclease enzyme and a methylase enzyme. While the host DNA is protected by methylation, invading DNA sequences without this methylation pattern are susceptible to cleavage by an endonuclease. However, the progeny of a single undetected virus particle will have a methylation pattern identical to the host and will no longer be recognized as an invader. Hence, an additional layer of defense against viral infection is based on clustered regularly interspaced short palindromic repeats (CRISPRs), which form the core of a sophisticated prokaryotic immune system that is both adaptive and inheritable.

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