The CMG Helicase Bypasses DNA-Protein Cross-Links to Facilitate Their Repair
The CMG Helicase Bypasses DNA-Protein Cross-Links to Facilitate Their Repair
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DOI：
10.1016/j.cell.2018.10.053
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发表时间：
2019-01-10
期刊：
影响因子：
64.5
通讯作者：
Walter, Johannes C.
中科院分区：
文献类型：
--
作者：
Sparks, Justin L.;Chistol, Gheorghe;Walter, Johannes C.
共价 DNA-蛋白质交联 (DPC) 阻碍复制叉进展并威胁基因组完整性。使用非洲爪蟾卵提取物，我们之前表明复制叉与 DPC 的碰撞会导致其蛋白水解，然后进行跨损伤 DNA 合成。我们在此表明，当 DPC 蛋白水解被阻断时，在前导链模板上移动的复制 DNA 解旋酶 CMG（CDC45、MCM2-7、GINS）会绕过完整的前导链 DPC。单分子成像显示，GINS 在旁路过程中不会与 CMG 解离，并且 CMG 在旁路后急剧减慢，可能是由于与停滞的前导链解偶联所致。 DNA 解旋酶 RTEL1 显然是通过在 DPC 之外产生单链 DNA 来促进旁路的。 RTEL1 的缺失会损害 DPC 蛋白水解作用，表明 CMG 必须绕过 DPC 才能实现蛋白水解作用。我们的结果提出了一种防止 DPC 蛋白酶无意中破坏 CMG 的机制，并且揭示了 CMG 克服其易位链上障碍的卓越能力。
Covalent DNA-protein cross-links (DPCs) impede replication fork progression and threaten genome integrity. Using Xenopus egg extracts, we previously showed that replication fork collision with DPCs causes their proteolysis, followed by translesion DNA synthesis. We show here that when DPC proteolysis is blocked, the replicative DNA helicase CMG (CDC45, MCM2-7, GINS), which travels on the leading strand template, bypasses an intact leading strand DPC. Single-molecule imaging reveals that GINS does not dissociate from CMG during bypass and that CMG slows dramatically after bypass, likely due to uncoupling from the stalled leading strand. The DNA helicase RTEL1 facilitates bypass, apparently by generating single-stranded DNA beyond the DPC. The absence of RTEL1 impairs DPC proteolysis, suggesting that CMG must bypass the DPC to enable proteolysis. Our results suggest a mechanism that prevents inadvertent CMG destruction by DPC proteases, and they reveal CMG's remarkable capacity to overcome obstacles on its translocation strand.