Genome-wide profiling of salt fractions maps physical properties of chromatin

We applied genome-wide profiling to successive salt-extracted fractions of micrococcal nuclease-treated Drosophila chromatin. Chromatin fractions extracted with 80mM or 150mM NaCl after digestion contain predominantly mononucleosomes and represent calssical 'active' chromatin. Profiles of these low-salt-soluble fractions display phased nucleosomes over transcriptionally active genes that are locally depleted of histone H3.3 and correspond closely to profiles of RNA polymerase II. Nearly quantitative recovery of chromatin is obtained with 600mM NaCl, however, the remaining insoluble chromatin is enriched in actively transcribed regions. Salt-insoluble chromatin likely represents oligonucleosomes that are attached to large protein complexes. Both low-salt extracted and insoluble chromatin are rich in sequences that correspond to epigenetic regulatory elements genome-wide. The presence of active chromatin at both extremes of salt solubility suggests that these salt fractions capture bound and unbound intermediates in active processes, thus providing a simple, powerful strategy for mapping epigenome dynamics. Keywords: Chromatin affinity-purification on microarray For data usage terms and conditions, please refer to http://www.genome.gov/27528022 and http://www.genome.gov/Pages/Research/ENCODE/ENCODEDataReleasePolicyFinal2008.pdf All experiments were done using two channels per chip, comparing DNAs extracted from either salt-extracted or insoluble chromatin to whole nuclear chromatin, whole nuclear chromatin to randomly fragmented genomic DNA, streptavidin-bound biotin-tagged histone-variant-containing chromatin to salt-extracted chromatin, gel-purified mononucleosomes to whole EDTA-extracted soluble chromatin, streptavidin-bound biotin-tagged histone-variant-containing chromatin to whole EDTA-extracted soluble chromatin, or oligo(dT)-primed cDNA to randomly fragmented genomic DNA from S2 cell nuclei.