dCas9::VP64 is an artificial transcriptional activator that contains a nuclease-dead form of the Streptococcus pyogenes Cas9 gene (contains mutations in both the RuvC domain (D10A) and in the HNH domain (H840A)) fused to the VP64 activation domain (FBrf0238848). dCas9::VP64 is used as a component of the synergistic activation mediator (SAM) system, to produce effective transcriptional activation of a gene of interest. In the SAM system, three components are combined: 1. an artificial transcriptional activator containing a nuclease-dead form of Cas9 (such as dCas9::VP64), 2. an sgRNA into which two Tag:MS2 stem loops have been inserted (one on the tetraloop and one on stem loop 2) and which targets sequence upstream of the gene of interest, and 3. a second transactivator protein which contains activation domain(s) fused to the coat protein of the MS2 RNA bacteriophage (Tag:MCP). The sgRNA targets the dCas9-containing component (such as dCas9::VP64) to the target site upstream of the gene of interest, while the Tag:MCP tag in the second transactivator protein binds specifically to the Tag:MS2 stem loop in the sgRNA, recruiting additional transcription activation domains to the assembled SAM complex (PMID:25494202). dCas9::VP64 has been shown to be effective as part of the SAM system in transgenic Drosophila ('flySAM', FBrf0238848) when combined with either the MCP::p65(m)::HSF1 or MCP::p65(h)::HSF1 transactivator protein. However, when used by itself in a two-component system with sgRNAs that do not contain the Tag:MS2 stem loops, dCas9::VP64 was unable to act as a transcriptional activator in transgenic flies (FBrf0229805).