Fig. 2
From: Precision cancer mouse models through genome editing with CRISPR-Cas9
CRISPR-Cas9 mechanism. a A single guide RNA (sgRNA) is a fusion between crRNA (CRISPR RNA) and tracrRNA (trans-activating CRISPR RNA). This complex recognizes the protospacer-adjacent motif (PAM) sequence and the complementary 20-nucleotide upstream genomic sequence. Cas9 cuts approximately three nucleotides upstream of the PAM to induce DNA double-strand breaks. Then, the cellular DNA repair system, either non-homologous end joining (NHEJ) or homology-directed repair (HDR), results in indels or precise editing, respectively. Cas9 proteins from different bacteria recognize different PAM sequences; S. pyogenes Cas9 recognizes ‘NGG’ PAM and the weaker ‘NAG’ PAM. b, c Key underlying principles for CRISPR-Cas approaches. b sgRNA targeting tumor suppressor genes can lead to loss-of-function frameshift mutations through NHEJ. c Template DNA can be used to introduce precise genome editing through HDR (for example, oncogene mutations). Dashed lines denote homologous recombination