During transcription, RNA polymerase II (Pol II) associates with the conserved elongation factor DSIF. DSIF renders the elongation complex stable and functions during Pol II pausing and RNA processing. We combined cryo-EM and X-ray crystallography to determine the structure of the mammalian Pol II–DSIF elongation complex at a nominal resolution of 3.4 Å. Human DSIF has a modular structure with two domains forming a DNA clamp, two domains forming an RNA clamp, and one domain buttressing the RNA clamp. The clamps maintain the transcription bubble, position upstream DNA, and retain the RNA transcript in the exit tunnel. The mobile C-terminal region of DSIF is located near exiting RNA, where it can recruit factors for RNA processing. The structure provides insight into the roles of DSIF during mRNA synthesis.

中文翻译：

---

转录RNA聚合酶II–DSIF复合物的结构揭示了多齿DNA–RNA钳

在转录过程中，RNA聚合酶II（Pol II）与保守的延伸因子DSIF结合。DSIF使延伸复合物稳定，并在Pol II暂停和RNA处理过程中发挥作用。我们结合了冷冻EM和X射线晶体学，确定了标称分辨率为3.4的哺乳动物Pol II–DSIF延伸复合物的结构。人DSIF具有模块化结构，其中两个结构域形成DNA钳位，两个结构域形成RNA钳位，一个结构域支撑RNA钳位。夹具保持转录气泡，将上游DNA定位，并将RNA转录物保留在出口通道中。DSIF的可移动C端区域位于存在的RNA附近，在那里可以募集因子进行RNA加工。该结构提供了对DSIF在mRNA合成过程中的作用的了解。