Department of Biochemistry and Cell Biology, University of Gothenburg, SE-405 30 Gothenburg, Sweden.
Nucleic Acids Res. 2011 Oct;39(19):8342-54. doi: 10.1093/nar/gkr551. Epub 2011 Jul 8.
The Mediator complex transmits activation signals from DNA bound transcription factors to the core transcription machinery. Genome wide localization studies have demonstrated that Mediator occupancy not only correlates with high levels of transcription, but that the complex also is present at transcriptionally silenced locations. We provide evidence that Mediator localization is guided by an interaction with histone tails, and that this interaction is regulated by their post-translational modifications. A quantitative, high-density genetic interaction map revealed links between Mediator components and factors affecting chromatin structure, especially histone deacetylases. Peptide binding assays demonstrated that pure wild-type Mediator forms stable complexes with the tails of Histone H3 and H4. These binding assays also showed Mediator-histone H4 peptide interactions are specifically inhibited by acetylation of the histone H4 lysine 16, a residue critical in transcriptional silencing. Finally, these findings were validated by tiling array analysis that revealed a broad correlation between Mediator and nucleosome occupancy in vivo, but a negative correlation between Mediator and nucleosomes acetylated at histone H4 lysine 16. Our studies show that chromatin structure and the acetylation state of histones are intimately connected to Mediator localization.
中介复合物将 DNA 结合转录因子的激活信号传递到核心转录机器。全基因组定位研究表明，中介复合物的占据不仅与高水平的转录相关，而且还存在于转录沉默的位置。我们提供的证据表明，中介复合物的定位是由与组蛋白尾部的相互作用指导的，并且这种相互作用受其翻译后修饰的调节。高密度遗传相互作用图谱揭示了中介复合物成分与影响染色质结构的因子之间的联系，尤其是组蛋白去乙酰化酶。肽结合实验证明，纯野生型中介复合物与组蛋白 H3 和 H4 的尾部形成稳定的复合物。这些结合实验还表明，组蛋白 H4 赖氨酸 16 的乙酰化特异性抑制中介复合物与组蛋白 H4 肽的相互作用，而赖氨酸 16 是转录沉默中关键的残基。最后，通过芯片分析验证了这些发现，该分析显示中介复合物与体内核小体占据之间存在广泛的相关性，但与组蛋白 H4 赖氨酸 16 乙酰化的核小体之间存在负相关。我们的研究表明，染色质结构和组蛋白的乙酰化状态与中介复合物的定位密切相关。
