H3K36me2 ChIP-chip

Set2p, which mediates histone H3 Lysine 36 dimethylation (H3K36me2) in Saccharomyces cerevisiae, has been shown to associate with RNA polymerase II (RNAP II) at individual loci. Here, ChIP-chip experiments normalized to general nucleosome occupancy reveal that nucleosomes within open reading frames (ORFs) and downstream non-coding chromatin were highly dimethylated at H3K36, and that Set2p activity begins at a stereotypic distance from the initiation of transcription genome-wide. H3K36me2 is scarce in regions upstream of divergently transcribed genes, telomeres, silenced mating loci, and regions transcribed by RNA polymerase III, providing evidence that the enzymatic activity of Set2p is restricted to its association with RNAP II. The presence of H3K36me2 within ORFs correlated with the "on" or "off" state of transcription, but the degree of H3K36 dimethylation within ORFs did not correlate with transcription frequency. This provides evidence that H3K36me2 is established during the initial instances of gene transcription, with subsequent transcription having at most a maintenance role. Accordingly, newly activated genes acquire H3K36me2 in a manner that does not correlate with gene transcript levels. Finally, nucleosomes dimethylated at H3K36 appear to be refractory to loss from highly transcribed chromatin. Thus H3K36me2, which is highly conserved throughout eukaryotic evolution, provides a stable molecular mechanism for establishing chromatin context throughout the genome by distinguishing potential regulatory regions from transcribed chromatin. Keywords: ChIP-chip Tweleve independent ChIP-chip experiments were performed using H3K36me2 specific antibody. The data was normalized using eight independent H4-myc ChIP-chip experiments. A control experiment was done in a strain in which SET2 had been deleted. The input DNA was used as a reference in all experiments. Direct comparison of the normalize data was done by performing ChIP-chips where the H4-myc ChIP DNA was used as the reference.