Chromatin architecture organized by histone variants H3.3 and H2A.Z in the human genome

To understand how chromatin structure is organized by different histone variants, we have measured the genome-wide distribution of nucleosome core particles (NCPs) containing the histone variants H3.3 and H2A.Z in human cells. We find that a special class of NCPs containing both variants is enriched at ‘nucleosome-free regions’ of active promoters, enhancers and insulator regions. We show that preparative methods used previously in studying nucleosome structure result in the loss of these unstable double-variant NCPs. It seems likely that this instability facilitates the access of transcription factors to promoters and other regulatory sites in vivo. Other combinations of variants have different distributions, consistent with distinct roles for histone variants in the modulation of gene expression. Overall design: genome-wide analysis of histone variants H2AZ, H3.3, and H3.3-H2A.Z double ChIP, plus input and genomic DNA controls in HeLa cells. H2A.Z samples are prepared under two different salt concentration conditions. (6 samples in total)