The chromatin remodeling protein, SRCAP, is critical for deposition of the histone variant H2A.Z at promoters

Studies in Saccharomyces cerevisiae indicate the histone variant H2A. Z is deposited at promoters by the chromatin remodeling protein Swr1 and plays a critical role in the regulation of transcription. In higher eukaryotes, however, little is known about the distribution, method of deposition, and function of H2A. Z at promoters. Using biochemical studies, we demonstrated previously that SRCAP ( SNF-2-related CREB-binding protein activator protein), the human ortholog of Swr1, could catalyze deposition of H2A. Z into nucleosomes. To address whether SRCAP directs H2A. Z deposition in vivo, promoters targeted by SRCAP were identified by a chromatin immunoprecipitation ( ChIP)-on-chip assay. ChIP assays on a subset of these promoters confirmed the presence of SRCAP on inactive and active promoters. The highest levels of SRCAP were observed on the active SP-1, G3BP, and FAD synthetase promoters. Detailed analyses of these promoters indicate sites of SRCAP binding overlap or occur adjacent to the sites of H2A. Z deposition. Knockdown of SRCAP levels using siRNA resulted in loss of SRCAP at these promoters, decreased deposition of H2A. Z and acetylated H2A. Z, and a decrease in levels of SP-1, G3BP, and FAD synthetase mRNA. Thus, these studies provide the first evidence that SRCAP is recruited to promoters and is critical for the deposition of H2A.