Figure 1.

Components of CRISPR/Cas9 system: (A). Genomic structures of the CRISPR/Cas system (top) and the engineered CRISPR/Cas9 system (bottom); (B). A schematic representation of the Cas9 protein structure. Domains includes REC (large recognition lobe) and RuvC (a nuclease domain), which is linked with an arginine-rich region. HNH is a second nuclease domain. PI is PAM-interacting domain; (C). The conformation of the Cas9–sgRNA complex in the process of DNA cleavage. The Cas9 endonuclease is targeted to DNA by a guide RNA which can be supplied as a two-part system consisting of crRNA and tracrRNA or as a single guide RNA, where the crRNA and tracrRNA are connected by a linker. Target recognition is facilitated by the protospacer-adjacent motif (PAM). Cleavage occurs on both strands (scissors) 3 bp upstream of the PAM.