Fig 1.
Outcomes of Cas9-single guide RNA (sgRNA) cleavage at a genomic site.
The Cas9-sgRNA complex is able to target a double-strand break in DNA to a specific site in the genome. The break is repaired by cellular machinery to generate a mutation that alters the site, thus preventing repeated cleavage. If the cell has a template that has homology to both sides of the break (left side of panel), then the template can be used by homology-dependent repair. For genome engineering, the investigator introduces into cells a custom template along with sources of Cas9 and the relevant sgRNA to create a designer mutation. Such mutations may be small changes in nucleotide sequence or a large insertion or deletion. Alternatively, the cell can use nonhomologous end joining (right side of panel) to create small insertions or deletions at the cut site.