Figure 1.

CRISPR/Cas9 and CRISPR/dCas9 systems. (A) CRISPR/Cas9 system. CRISPR/Cas9 system consists of a sgRNA (a chimeric of crRNA and tracrRNA) and Cas9. crRNA is a targeting sequence while tracrRNA functions as a Cas9 nuclease-recruiting sequence. Cas9 possess a nuclease activity to cleave the target DNA and induces a DNA double-strand break through nicking each strand of DNA by RuvC1 and HNH domains. (B) CRISPR/dCas9 fusion protein. dCas9 is nuclease-defective but posses DNA binding ability. dCas9 is derived by introducing two silencing mutations (D10A and H840A) on the RuvC1 and HNH domains, respectively. dCas9 is fused to an effector domain for targeted epigenome editing or transcriptional modulation.