Sarker Altaf H, Tsutakawa Susan E, Kostek Seth, Ng Cliff, Shin David S, Peris Marian, Campeau Eric, Tainer John A, Nogales Eva, Cooper Priscilla K
Life Sciences Division, Lawrence Berkeley National Laboratory, 1 Cyclotron Road, Mail Stop 74R157, Berkeley, California 94720, USA.
Mol Cell. 2005 Oct 28;20(2):187-98. doi: 10.1016/j.molcel.2005.09.022.
Loss of a nonenzymatic function of XPG results in defective transcription-coupled repair (TCR), Cockayne syndrome (CS), and early death, but the molecular basis for these phenotypes is unknown. Mutation of CSB, CSA, or the TFIIH helicases XPB and XPD can also cause defective TCR and CS. We show that XPG interacts with elongating RNA polymerase II (RNAPII) in the cell and binds stalled RNAPII ternary complexes in vitro both independently and cooperatively with CSB. XPG binds transcription-sized DNA bubbles through two domains not required for incision and functionally interacts with CSB on these bubbles to stimulate its ATPase activity. Bound RNAPII blocks bubble incision by XPG, but an ATP hydrolysis-dependent process involving TFIIH creates access to the junction, allowing incision. Together, these results implicate coordinated recognition of stalled transcription by XPG and CSB in TCR initiation and suggest that TFIIH-dependent remodeling of stalled RNAPII without release may be sufficient to allow repair.
XPG非酶功能的丧失会导致转录偶联修复（TCR）缺陷、科凯恩综合征（CS）以及过早死亡，但这些表型的分子基础尚不清楚。CSB、CSA或TFIIH解旋酶XPB和XPD的突变也会导致TCR缺陷和CS。我们发现，XPG在细胞中与延伸的RNA聚合酶II（RNAPII）相互作用，并且在体外既能独立又能与CSB协同结合停滞的RNAPII三元复合物。XPG通过两个切割不需要的结构域结合转录大小的DNA气泡，并在这些气泡上与CSB发生功能相互作用以刺激其ATP酶活性。结合的RNAPII会阻止XPG对气泡的切割，但一个涉及TFIIH的ATP水解依赖性过程会创造进入连接点的通道，从而允许切割。这些结果共同表明，XPG和CSB在TCR起始过程中对停滞转录的协同识别，并且表明依赖TFIIH对停滞RNAPII进行的不释放的重塑可能足以允许修复。
