Practice question

Type II CRISPR system of Streptococcus pyogenes minimal interference module requires trans-activating crRNA tracrRNA. Pre-crRNA containing repeats is annealed to tracrRNA forming duplex recognized by RNase III for processing into mature guide RNAs. TracrRNA also hybridizes to crRNA to form dual guide structure that activates Cas9 conformational change enabling PAM scanning and DNA cleavage. Unlike type I requiring Cas3 helicase nuclease or type V using Cas12 alone, type II canonical system depends on tracrRNA for biogenesis and Cas9 loading, later fused as single guide RNA.