CRISPR/Cas (clustered Regularly Interspaced Short Palindromic Repeats /CRISP-associated proteins) system is a prokaryotic antiviral resistance mechanism which constitutes the only documented bacterial adaptive immune system. The adaptive feature of CRISPR-Cas immune system relies on its ability to integrate foreign short DNA sequences of invading molecules and integrate them in between the repetitive sequences of the CRISPR array in the form of
Following transcription and processing of these loci, the CRISPR antisens RNAs (crRNAs) guide the Cas proteins to complementary invading nucleic acid, which results in target interference.
The acquisition of new spacers allows the CRISPR-Cas immune system to rapidly adapt against new threats .
Bacterial viruses have developed strategies to circumvent this bacterial defense . Gene 35 from the Pseudomonas phage JBD30 encodes a protein able to suppress the CRISPR system, most probably after the crRNA biogenesis.
The vibrio cholera phage ICP1 instead encodes its own CRISPR/Cas system to counteract a phage inhibitory chromosomal island of the bacterial host .