Chromatin Dynamics and the RNA Exosome Function in Concert to Regulate Transcriptional Homeostasis

• H3-K56Ac and H2A.Z stimulate expression of promoter-associated, divergent ncRNAs
• Global transcriptional roles for H3-K56Ac are masked by the nuclear RNA exosome
• H2A.Z functions with the RNA exosome to repress expression of a subset of ncRNAs
• H3-K56ac and H2A.Z facilitate formation of chromosome interaction domains

SummaryThe histone variant H2A.Z is a hallmark of nucleosomes flanking promoters of protein-coding genes and is often found in nucleosomes that carry lysine 56-acetylated histone H3 (H3-K56Ac), a mark that promotes replication-independent nucleosome turnover. Here, we find that H3-K56Ac promotes RNA polymerase II occupancy at many protein-coding and noncoding loci, yet neither H3-K56Ac nor H2A.Z has a significant impact on steady-state mRNA levels in yeast. Instead, broad effects of H3-K56Ac or H2A.Z on RNA levels are revealed only in the absence of the nuclear RNA exosome. H2A.Z is also necessary for the expression of divergent, promoter-proximal noncoding RNAs (ncRNAs) in mouse embryonic stem cells. Finally, we show that H2A.Z functions with H3-K56Ac to facilitate formation of chromosome interaction domains (CIDs). Our study suggests that H2A.Z and H3-K56Ac work in concert with the RNA exosome to control mRNA and ncRNA expression, perhaps in part by regulating higher-order chromatin structures.

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