 Many bacteria and most archaea have an adaptive immune system which incorporates CRISPR RNA (crRNA) and CRISPR-associated (cas) genes.The CRISPR interference (CRISPRi) technique was first reported by Lei S. Qi and researchers at the University of California at San Francisco in early 2013.The technology uses a catalytically dead Cas9 (usually denoted as dCas9) protein that lacks endonuclease activity to regulate genes in an RNA-guided manner.