Practice question

Cas9 is dual nuclease utilizing HNH domain to cut target strand complementary to guide RNA and RuvC domain to cut non-target strand simultaneously. Both nicks occur three base pairs upstream of PAM on opposite strands, generating predominantly blunt ended double strand breaks without single stranded overhangs. Such blunt breaks are predominantly repaired by non-homologous end joining causing small indels, or by homology directed repair if donor template provided. Blunt nature facilitates efficient ligation mediated insertion and predictable editing outcomes in genome engineering laboratories worldwide.