The eukaryotic replisome is assembled around the CMG (CDC45-MCM-GINS) replicative helicase, which encircles the leading-strand DNA template at replication forks. When CMG stalls during DNA replication termination, or at barriers such as DNA-protein crosslinks on the leading strand template, a second helicase is deployed on the lagging strand template to support replisome progression. How these 'accessory' helicases are targeted to the replisome to mediate barrier bypass and replication termination remains unknown. Here, by combining AlphaFold structural modelling with experimental validation, we show that the budding yeast Rrm3 accessory helicase contains two Short Linear Interaction Motifs (SLIMs) in its disordered N-terminus, which interact with CMG and the leading-strand DNA polymerase Polε on one side of the replisome. This flexible tether positions Rrm3 adjacent to the lagging strand template on which it translocates, and is critical for replication termination in vitro and Rrm3 function in vivo. The primary accessory helicase in metazoa, RTEL1, is evolutionarily unrelated to Rrm3, but binds to CMG and Polε in an analogous manner, revealing a conserved docking mechanism for accessory helicases in the eukaryotic replisome.

中文翻译：

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将 Rrm3 和 RTEL1 辅助解旋酶招募到真核复制体的常见机制。


真核复制体围绕 CMG (CDC45-MCM-GINS) 复制解旋酶组装，该解旋酶在复制叉处环绕前导链 DNA 模板。当 CMG 在 DNA 复制终止期间或在前导链模板上的 DNA-蛋白质交联等障碍处停滞时，第二个解旋酶会部署在滞后链模板上以支持复制体进展。这些“辅助”解旋酶如何靶向复制体以介导屏障旁路和复制终止仍然未知。在这里，通过将 AlphaFold 结构模型与实验验证相结合，我们发现出芽酵母 Rrm3 辅助解旋酶在其无序 N 末端包含两个短线性相互作用基序 (SLIM)，它们与 CMG 和前导链 DNA 聚合酶 Polε 相互作用复制体的一侧。这种灵活的系链将 Rrm3 定位在其易位的滞后链模板附近，对于体外复制终止和体内 Rrm3 功能至关重要。后生动物中的主要辅助解旋酶 RTEL1 在进化上与 Rrm3 无关，但以类似的方式与 CMG 和 Polε 结合，揭示了真核复制体中辅助解旋酶的保守对接机制。