Transcription-coupled DNA repair removes bulky DNA lesions from the genome^1,2 and protects cells against ultraviolet (UV) irradiation³. Transcription-coupled DNA repair begins when RNA polymerase II (Pol II) stalls at a DNA lesion and recruits the Cockayne syndrome protein CSB, the E3 ubiquitin ligase, CRL4^CSA and UV-stimulated scaffold protein A (UVSSA)³. Here we provide five high-resolution structures of Pol II transcription complexes containing human transcription-coupled DNA repair factors and the elongation factors PAF1 complex (PAF) and SPT6. Together with biochemical and published^3,4 data, the structures provide a model for transcription–repair coupling. Stalling of Pol II at a DNA lesion triggers replacement of the elongation factor DSIF by CSB, which binds to PAF and moves upstream DNA to SPT6. The resulting elongation complex, EC^TCR, uses the CSA-stimulated translocase activity of CSB to pull on upstream DNA and push Pol II forward. If the lesion cannot be bypassed, CRL4^CSA spans over the Pol II clamp and ubiquitylates the RPB1 residue K1268, enabling recruitment of TFIIH to UVSSA and DNA repair. Conformational changes in CRL4^CSA lead to ubiquitylation of CSB and to release of transcription-coupled DNA repair factors before transcription may continue over repaired DNA.

转录偶联 DNA 修复可去除基因组^1,2中的大量 DNA 损伤，并保护细胞免受紫外线 (UV) 照射³。^{当 RNA 聚合酶 II (Pol II) 在 DNA 损伤处停止并募集 Cockayne 综合征蛋白 CSB、E3 泛素连接酶、CRL4 CSA}和紫外线刺激的支架蛋白 A (UVSSA) ³时，转录偶联 DNA 修复就开始了。在这里，我们提供了 Pol II 转录复合物的五种高分辨率结构，其中包含人类转录偶联 DNA 修复因子和延伸因子 PAF1 复合物 (PAF) 和 SPT6。连同生化并发表^3,4数据，这些结构为转录 - 修复耦合提供了一个模型。Pol II 在 DNA 损伤处的停滞会触发 CSB 取代延伸因子 DSIF，CSB 与 PAF 结合并将上游 DNA 移动到 SPT6。由此产生的延伸复合物 EC ^TCR使用 CSA 刺激的 CSB 转位酶活性来拉动上游 DNA 并推动 Pol II 前进。如果病变无法绕过，CRL4 ^CSA跨越 Pol II 钳并泛素化 RPB1 残基 K1268，使 TFIIH 能够募集到 UVSSA 和 DNA 修复。CRL4 ^CSA的构象变化导致 CSB 的泛素化和转录偶联 DNA 修复因子的释放，然后转录可能继续超过修复的 DNA。