Cas9 gRNA engineering for genome editing, activation and repression

The length of a single guide RNA (gRNA) determines the function of Cas9. In this study 20-nt gRNAs allowed nuclease activity and genome editing, whereas 14-nt gRNAs mediated transcriptional activation or repression. We demonstrate that by altering the length of Cas9-associated guide RNA (gRNA) we were able to control Cas9 nuclease activity and simultaneously perform genome editing and transcriptional regulation with a single Cas9 protein. We exploited these principles to engineer mammalian synthetic circuits with combined transcriptional regulation and kill functions governed by a single multifunctional Cas9 protein.