Mediator, TATA-binding Protein, and RNA Polymerase II Contribute to Low Histone Occupancy at Active Gene Promoters in Yeast
Mediator, TATA-binding Protein, and RNA Polymerase II Contribute to Low Histone Occupancy at Active Gene Promoters in Yeast
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DOI：
10.1074/jbc.m113.529354
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发表时间：
2014-05-23
影响因子：
4.8
通讯作者：
Morse, Randall H.
中科院分区：
文献类型：
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作者：
Ansari, Suraiya A.;Paul, Emily;Morse, Randall H.
真核生物中 RNA 聚合酶 II (Pol II) 的转录需要介体复合物，并且通常涉及活性启动子处的染色质重塑和组蛋白驱逐。在这里，我们探讨了介体在招募 Swi/Snf 染色质重塑复合物中的作用，及其与预起始复合物 (PIC) 成分一起在芽殖酵母酿酒酵母中诱导型和组成型活性启动子组蛋白驱逐中的作用。我们表明，Swi/Snf 染色质重塑复合物向诱导的 CHA1 启动子的募集，以及其与几个组成型活性启动子的关联，取决于介体复合物，但独立于诱导的 MET2 和 MET6 基因的介体。尽管 CHA1 的转录激活和组蛋白驱逐取决于 Swi/Snf，但 Swi/Snf 的募集不足以导致诱导的 CHA1 启动子处的组蛋白驱逐。 Swi/Snf 活性的丧失不会影响几个组成型活性启动子的组蛋白占据；相反，在介体和 PIC 组分突变体中，这些启动子处观察到较高的组蛋白占据率。我们提出，最初的激活剂依赖性核小体重塑步骤允许 PIC 成分在启动子序列的占据上胜过组蛋白。我们还观察到 Pol II (rpb1-1) 突变体中介体和 TATA 结合蛋白的启动子关联减少，表明转录机制的这些组件相互协作结合，并表明 PIC 作为一个整体，其结合导致稳定的组蛋白驱逐。
Transcription by RNA polymerase II (Pol II) in eukaryotes requires the Mediator complex, and often involves chromatin remodeling and histone eviction at active promoters. Here we address the role of Mediator in recruitment of the Swi/Snf chromatin remodeling complex and its role, along with components of the preinitiation complex (PIC), in histone eviction at inducible and constitutively active promoters in the budding yeast Saccharomyces cerevisiae. We show that recruitment of the Swi/Snf chromatin remodeling complex to the induced CHA1 promoter, as well as its association with several constitutively active promoters, depends on the Mediator complex but is independent of Mediator at the induced MET2 and MET6 genes. Although transcriptional activation and histone eviction at CHA1 depends on Swi/Snf, Swi/Snf recruitment is not sufficient for histone eviction at the induced CHA1 promoter. Loss of Swi/ Snf activity does not affect histone occupancy of several constitutively active promoters; in contrast, higher histone occupancy is seen at these promoters in Mediator and PIC component mutants. We propose that an initial activator-dependent, nucleosome remodeling step allows PIC components to outcompete histones for occupancy of promoter sequences. We also observe reduced promoter association of Mediator and TATA-binding protein in a Pol II (rpb1-1) mutant, indicating mutually cooperative binding of these components of the transcription machinery and indicating that it is the PIC as a whole whose binding results in stable histone eviction.