Transcription by RNA polymerase II (Pol II) is carried out by an elongation complex. We previously reported an activated porcine Pol II elongation complex, EC*, encompassing the human elongation factors DSIF, PAF1 complex (PAF) and SPT6. Here we report the cryo-EM structure of the complete EC* that contains RTF1, a dissociable PAF subunit critical for chromatin transcription. The RTF1 Plus3 domain associates with Pol II subunit RPB12 and the phosphorylated C-terminal region of DSIF subunit SPT5. RTF1 also forms four α-helices that extend from the Plus3 domain along the Pol II protrusion and RPB10 to the polymerase funnel. The C-terminal ‘fastener’ helix retains PAF and is followed by a ‘latch’ that reaches the end of the bridge helix, a flexible element of the Pol II active site. RTF1 strongly stimulates Pol II elongation, and this requires the latch, possibly suggesting that RTF1 activates transcription allosterically by influencing Pol II translocation.

RNA 聚合酶 II (Pol II) 的转录是通过延伸复合物进行的。我们之前报道了一种活化的猪 Pol II 延伸复合物 EC*，包括人类延伸因子 DSIF、PAF1 复合物 (PAF) 和 SPT6。在这里，我们报告了包含 RTF1 的完整 EC* 的冷冻电镜结构，RTF1 是一种对染色质转录至关重要的可解离的 PAF 亚基。RTF1 Plus3 域与 Pol II 亚基 RPB12 和 DSIF 亚基 SPT5 的磷酸化 C 末端区域相关。RTF1 还形成四个 α-螺旋，从 Plus3 结构域沿 Pol II 突起和 RPB10 延伸到聚合酶漏斗。C 端“紧固件”螺旋保留了 PAF，然后是一个“闩锁”，到达桥螺旋的末端，这是 Pol II 活性位点的灵活元件。RTF1 强烈刺激 Pol II 伸长，