Stirring Up the Type V Alphabet Soup.

Type II and type V CRISPR-Cas effectors are multidomain enzymes that utilize a guide RNA to bind and cleave complementary DNA targets.1 The facile programmability of these effectors allows for their exploitation as genome editing tools. While the type II effector Cas9 is undoubtedly the best-known genome editing tool, the more recently characterized type V effectors (i.e., Cas12a and Cas12b) have also been repurposed for genome editing.1–3

Despite their highly similar functionality, Cas9 and Cas12 have distinct domain architectures and mechanisms, making them complementary tools for genome editing.1 Strikingly, there is a high diversity in sequence and domain organization among the different type V effectors.4,5 Therefore, characterization of these functionally diverse type V effectors could lead to the expansion of the CRISPR toolbox. Writing in Science,6 Yan et al. from Arbor Biotechnologies and the National Center for Biotechnology Information have extended the type V alphabet by identifying and characterizing four novel type V effectors: type V-C Cas12c type V-G Cas12g, type V-H Cas12h, and type V-I Cas12i.