Clustered regularly interspaced short palindromic repeats cas systems: a comprehensive review.

The clustered regularly interspaced short palindromic repeats (CRISPR) system was recently identified as a bacterial defense mechanism against phages and plasmids. The CRISPR system is composed of DNA arrays containing short sequences identical to those present in phages and plasmids. These short DNAs are transcribed and processed by CRISPR associated proteins that also guide other CRISPR proteins to target the invading DNA. Only a few of the CRISPR components have been characterized to date, and their mechanism of action is still largely unknown. Phage defense mechanisms probably have co-evolved against the CRISPR system, but none has yet been found. We propose to identify phage genes that counteract the CRISPR system.