Eukaryotic gene transcription is carried out by three RNA polymerases: Pol I, Pol II and Pol III. Although it has long been known that Pol I can form homodimers, it is unclear whether and how the two other RNA polymerases dimerize. Here we present the cryo-electron microscopy (cryo-EM) structure of a mammalian Pol II dimer at 3.5 Å resolution. The structure differs from the Pol I dimer and reveals that one Pol II copy uses its RPB4-RPB7 stalk to penetrate the active centre cleft of the other copy, and vice versa, giving rise to a molecular handshake. The polymerase clamp domain is displaced and mobile, and the RPB7 oligonucleotide-binding fold mimics the DNA–RNA hybrid that occupies the cleft during active transcription. The Pol II dimer is incompatible with nucleic acid binding as required for transcription and may represent an inactive storage form of the polymerase.

中文翻译：

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无活性 RNA 聚合酶 II 二聚体的结构

真核基因转录由三种 RNA 聚合酶进行：Pol I、Pol II 和 Pol III。尽管人们早就知道 Pol I 可以形成同型二聚体，但尚不清楚其他两种 RNA 聚合酶是否以及如何二聚化。在这里，我们展示了哺乳动物 Pol II 二聚体的低温电子显微镜 (cryo-EM) 结构，分辨率为 3.5 Å。该结构与 Pol I 二聚体不同，表明一个 Pol II 拷贝使用其 RPB4-RPB7 茎杆穿透另一个拷贝的活性中心裂隙，反之亦然，从而产生分子握手。聚合酶钳结构域被置换和移动，RPB7 寡核苷酸结合折叠模拟了活跃转录过程中占据裂缝的 DNA-RNA 杂合体。