The ISCB protein family is an ancestral form of Cas9, is about one-third the size, and possesses helicase and nuclease activity but requires a larger guide RNA.

“in in one of our projects trying to look for a small cast n uh we thought let's look at the evolutionary origin of where Cai came from and by tracing the The evolutionary history of casai we found that there is a very large family protein called iscb um that is um The ancestral form of cine ISB is a very small protein it's only about 450 mes uh so it's about a third of the size of casai and it does exactly what casai does it's got a hilas activity it's got nucleus domains and it also works with the RNA guide to recognize and cleave DNA”