Fig. 2

Schematic of the CRISPR/Cas9 system. Cas9 nuclease is directed by small guide (sg)RNA to cleave the desired DNA sequences. The first 20-nt of the sgRNA recognize its targeted DNA through base-paring interaction. A PAM motif on the DNA target is required for the enzymatic activity of Cas9 protein. The RuvC and HNH endonuclease domains of Cas9 cleaves one strand of DNA, respectively, to generate a double-stranded DNA break approximately 3 bp upstream of the PAM