Question

Describe in detail the CRISPR-Cas9 system of defense in bacterial against phages.

Answer 1

CRISPR -Cas9 system is found in bacteria`s and it is part of the bacterial `adaptive immune system` against bacteriophages.

bacteriophages attach tot he bacterial cells and inject the DNA into the host cell, Cas complex in the bacteria cleave the incoming phage DNA into small pieces, and one of the pieces called spacer is inserted into the CRISPR locus, upon the second infection by the same phage, CRISPR locus is transcribed to CRISPR RNA, which is then processed by RNase III to small pieces then TracrRNA and Cas9 endonuclease associate with small RNAs and Cas9 endonuclease is guided to the phage DNA, Cas9 endnuclease cuts near PAM sequence in the target DNA so the infection is prevented.