Question

2.How are Cas5 and Cas9 related? What is an HNH motif? Please give citations.

Answer 1

Cas9 is an RNA guided DNA endonuclease enzyme which is important and related with the CRISPR adaptive immunity system in Streptococcus pyogenes. It helps in cleaving the foreign DNA. Cas5 helps in stabilizing the pre-crDna into crRNA units. Both of them are related as they are important part of the immune system and are part of the CRISPR-Cas system that is mandatory for the prokaryotic defense mechanism. It helps in providing defense in prokaryotes. The HNH motif is present in many enzymes and is a catalytic center for the homing endonucleases. There are number of proteins that fall in the HNH superfamily like the endonucleases, colicins, restriction endonucleases, transposases and DNA packaging factors.