Clustered regularly interspaced short palindromic repeats cas systems: a comprehensive review
The CRISPR system, a recently discovered defense mechanism, is described, which is remarkable because it confers acquired phage resistance in Bacteria and Archaea and investigates ABSTRACT.
Abstract
Bacteriophages constitute the most populous life-forms on Earth.1 In sea water, an environment in which phage abundance has been extensively studied, it has been estimated that there is 5-10 phage for every bacterial cell.2 Despite being outnumbered by the phage, bacteria proliferate and avoid extinction by using a battery of innate phage resistance mechanisms such as restriction enzymes and abortive infection.3 In this Progress article, we describe the CRISPR system, a recently discovered defense mechanism, which is remarkable because it confers acquired phage resistance in Bacteria and Archaea. A hallmark of this system is arrayed of short direct repeats interspersed by nonrepetitive spacer sequences, the so-called clustered regularly interspaced short palindromic repeats (CRISPR). Additional components of the system include CRISPR associated (CAS) genes and a leader sequence. The recently discovered CRISPR-Cas adaptive immune system is present in almost all archaea and many bacteria. It consists of cassettes of CRISPR repeats that incorporate spacers homologous to fragments of viral or plasmid genomes that are employed as guide RNAs in the immune response, along with numerous CRISPR-associated (cas) genes that encode proteins possessing diverse, only partially characterized activities required for the action of the system. Here, we investigate ABSTRACT