Histone H3 Lysine 36 Methylation Antagonizes Silencing in Saccharomyces cerevisiae Independently of the Rpd3S Histone Deacetylase Complex

摘要

In yeast, methylation of histone H3 on lysine 36 (H3-K36) is catalyzed by the NSD1 leukemia oncoproteinnhomolog Set2. The histone deacetylase complex Rpd3S is recruited to chromatin via binding ofnthe chromodomain protein Eaf3 to methylated H3-K36 to prevent erroneous transcription initiation.nHere we identify a distinct function for H3-K36 methylation. We used random mutagenesis of histones H3nand H4 followed by a reporter-based screen to identify residues necessary to prevent the ectopic spreadnof silencing from the silent mating-type locus HMRa into flanking euchromatin. Mutations in H3-K36nor deletion of SET2 caused ectopic silencing of a heterochromatin-adjacent reporter. Transcriptionalnprofiling revealed that telomere-proximal genes are enriched for those that display decreased expressionnin a set2D strain. Deletion of SIR4 rescued the expression defect of 26 of 37 telomere-proximal genes withnreduced expression in set2D cells, implying that H3-K36 methylation prevents the spread of telomericnsilencing. Indeed, Sir3 spreads from heterochromatin into neighboring euchromatin in set2D cells.nFurthermore, genetic experiments demonstrated that cells lacking the Rpd3S-specific subunits Eaf3 ornRco1 did not display the anti-silencing phenotype of mutations in SET2 or H3-K36. Thus, antagonism ofnsilencing is independent of the only known effector of this conserved histone modification