In eukaryotes, RNA polymerase (Pol) II transcribes chromatin and must move past nucleosomes, often resulting in nucleosome displacement. How Pol II unwraps the DNA from nucleosomes to allow transcription and how DNA rewraps to retain nucleosomes has been unclear. Here, we report the 3.0-angstrom cryo–electron microscopy structure of a mammalian Pol II-DSIF-SPT6-PAF1c-TFIIS-nucleosome complex stalled 54 base pairs within the nucleosome. The structure provides a mechanistic basis for nucleosome retention during transcription elongation where upstream DNA emerging from the Pol II cleft has rewrapped the proximal side of the nucleosome. The structure uncovers a direct role for Pol II and transcription elongation factors in nucleosome retention and explains how nucleosomes are retained to prevent the disruption of chromatin structure across actively transcribed genes.

中文翻译：

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转录延伸过程中核小体保留的结构基础

在真核生物中，RNA 聚合酶 (Pol) II 转录染色质并且必须通过核小体，通常导致核小体移位。Pol II 如何从核小体中解开 DNA 以允许转录，以及 DNA 如何重新包装以保留核小体尚不清楚。在这里，我们报告了哺乳动物 Pol II-DSIF-SPT6-PAF1c-TFIIS-核小体复合物的 3.0 埃低温电子显微镜结构在核小体内停滞了 54 个碱基对。该结构为转录延伸过程中的核小体保留提供了机械基础，其中从 Pol II 裂缝出现的上游 DNA 重新包裹了核小体的近侧。