CRISPR?Cas system utilizes short RNA molecule called as CRISPR RNAs (crRNAs) to identify target DNA sequences.The cascade complex processes the crRNA array transcript into mature crRNA or the guide RNA (gRNA) which servesas a guide for target binding. Target recognition via cascade depends on Protospacer adjacent motifs (PAM) which is a short conserved 2?5bp DNA sequence located next to the target DNA that is essential to mark the target site. In order to achieve gene silencing two essential components are required Cascade and crRNA.