CRISPR en crRNA's

Bacteria continuously face infections from bacteriophages, viruses that infect bacteria.

To deal with this threat, bacteria have evolved a sophisticated adaptive immunity system known as the CRISPR-Cas system to destroy bacteriophage DNA, in case of reinfection.  

This system involves three different processes – incorporation of the bacteriophage DNA segment into the bacterial genome, production of the CRISPR RNA and the Cas protein, and CRISPR RNA-Cas mediated cleavage of the bacteriophage DNA.

When a bacteriophage attacks, it attaches to the surface of the bacterial cell and inserts its DNA into the bacteria which is then cleaved by the bacterial system. 

A short segment of the bacteriophage DNA is then added into specific regions of the bacterial genome, called CRISPR, clustered regularly interspaced short palindromic repeats. These are genomic regions where bacterial sequence repeats are interspersed with the short varying spacer sequences from different bacteriophages.

These spacer sequences serve as a memory for the bacteria of all the bacteriophages that have previously attacked. Bacteria use spacer sequences to rapidly identify and destroy DNA from a particular type of bact