fig2

Figure 2. Mechanism of the CRISPR/Cas9 gene editing system. The single guide RNA (sgRNA) directs the Cas9 nuclease to a complementary genomic sequence, where Cas9 induces a double-strand break (DSB). The target sequence must be adjacent to a 5′-NGG-3′ protospacer adjacent motif (PAM) for Cas9 activity. The DSB is repaired either by non-homologous end joining (NHEJ) or homology-directed repair (HDR), the latter of which can utilize a DNA repair template to introduce precise genetic modifications or exogenous sequences ^[25].