Fig. 2

Schematic of various CRISPR-Cas9 functions. A Classical CRISPR/Cas9 works as genetic scissors for a specific edition. The Cas9 nuclease (light blue) recognizes 3′ PAM sequence (NGG, NAG) (pink) and target DNA pairs with complementary sgRNA (purple), followed by the formation of blunt DNA double-stranded breaks at the target site (red). Cas9 was fused with selected proteins to induce distinct biological effects (B–D). B dCas9 protein fuses to the cytosine deaminase APOBEC1 (light green) and the uracil DNA glycosylase inhibitor (UGI, orange) to form cytosine base editor. The dCas9 component enables the guidance to its target sequence, then the APOBEC1 component induces C to T conversion. C Cas9 nickase fuse with reverse transcriptase (RT, green) to form prime editors. The prime-editing guide RNA (pegRNA, purple) binds to its complementary target DNA, and the unbound DNA of the PAM-containing strand is cleaved by Cas9. This creates a complementary primer for the desired sequence on the pegRNA, and the RT actively extended the unbound DNA using the pegRNA as a template. D dCas9 fuses to transcriptional activator or repressor (purple) to create CRISPRa and CRISPRi tools and enable target gene transcription regulation