Sigma has developed a gene activation system based on a fusion of dCas9 to the catalytic histone acetyltransferase (HAT) core domain of the human E1A-associated protein p300. This approach has been independently validated by the Gersbach lab (Duke University) to activate genes at both proximal and distal locations relative the transcriptional start site (TSS). The dCas9-p300 histone acetylation approach represents a distinct mechanism of action relative to dCas9-VP64 or other similar gene activation motifs. While activation domains, such as VP64, help recruit transcription complexes to the promoter region, they are at the mercy of the epigenetic state of the gene and dependent on the availability of additional transcriptional proteins. Conversely, the p300 histone acetyltransferase protein opens a transcriptional highway by releasing the DNA from its heterochromatin state and allowing for continued and robust gene expression by the endogenous cellular machinery.