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首页> 外文期刊>Molecular and Cellular Biology >Recruitment of the Nucleolar Remodeling Complex NoRC Establishes Ribosomal DNA Silencing in Chromatin
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Recruitment of the Nucleolar Remodeling Complex NoRC Establishes Ribosomal DNA Silencing in Chromatin

机译：核仁重塑复合体NoRC的招聘建立了染色质中的核糖体DNA沉默。

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摘要

The rRNA gene cluster consists of multiple transcription units. Half of these are active, while the other half are transcriptionally inactive. Previously, in vivo studies have demonstrated that silencing of ribosomal DNA (rDNA) is mediated by the chromatin remodeling NoRC (nucleolar remodeling complex). To explore the mechanisms underlying NoRC-directed silencing of rDNA transcription, we investigated the effect of recombinant NoRC on RNA polymerase I transcription on reconstituted chromatin templates. We show that NoRC interacts with the transcription terminator factor (TTF-I), and this interaction is required both for the binding of TTF-I to its promoter-proximal target site and for the recruitment of NoRC to the promoter. After association with the rDNA promoter, NoRC alters the position of the promoter-bound nucleosome, thereby repressing RNA polymerase I transcription. This NoRC-directed rDNA repression requires the N terminus of histone H4. Repression is effective before preinitiation complex formation and as such is unable to exert an effect upon activated rDNA genes. Furthermore, the early steps of rDNA repression do not depend on DNA and histone modifications. These results reveal an important role for TTF-I in recruiting NoRC to rDNA and an active role for NoRC in the establishment of rDNA silencing.
机译：rRNA基因簇由多个转录单位组成。其中一半是有活性的，而另一半是转录无活性的。以前，体内研究表明核糖体DNA（rDNA）的沉默是由染色质重塑NoRC（核仁重塑复合物）介导的。为了探讨潜在的NoRC指导沉默的rDNA转录的机制，我们调查了重组NoRC对重组染色质模板上RNA聚合酶I转录的影响。我们显示，NoRC与转录终止因子（TTF-1）相互作用，并且这种相互作用对于TTF-1与其启动子附近的靶位点的结合以及NoRC募集到启动子都是必需的。与rDNA启动子缔合后，NoRC改变了启动子结合的核小体的位置，从而抑制了RNA聚合酶I的转录。这种由NoRC指导的rDNA阻遏需要组蛋白H4的N末端。抑制在预启动复合物形成之前是有效的，因此不能对活化的rDNA基因产生影响。此外，rDNA抑制的早期步骤不依赖于DNA和组蛋白修饰。这些结果揭示了TTF-1在将NoRC募集到rDNA中的重要作用以及对于NoRC在rDNA沉默的建立中的积极作用。

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