The MRC Protein Phosphorylation and Ubiquitylation Unit, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK.
Genome Damage and Stability Centre, Department of Life Sciences, University of Sussex, Brighton BN1 9RQ, UK.
Mol Cell. 2019 Apr 18;74(2):231-244.e9. doi: 10.1016/j.molcel.2019.01.040. Epub 2019 Mar 5.
The convergence of two DNA replication forks creates unique problems during DNA replication termination. In E. coli and SV40, the release of torsional strain by type II topoisomerases is critical for converging replisomes to complete DNA synthesis, but the pathways that mediate fork convergence in eukaryotes are unknown. We studied the convergence of reconstituted yeast replication forks that include all core replisome components and both type I and type II topoisomerases. We found that most converging forks stall at a very late stage, indicating a role for additional factors. We showed that the Pif1 and Rrm3 DNA helicases promote efficient fork convergence and completion of DNA synthesis, even in the absence of type II topoisomerase. Furthermore, Rrm3 and Pif1 are also important for termination of plasmid DNA replication in vivo. These findings identify a eukaryotic pathway for DNA replication termination that is distinct from previously characterized prokaryotic mechanisms.
两个 DNA 复制叉的汇聚在 DNA 复制终止时会产生独特的问题。在大肠杆菌和 SV40 中，II 型拓扑异构酶释放扭转应变对于汇聚的复制体完成 DNA 合成至关重要，但真核生物中介导叉汇聚的途径尚不清楚。我们研究了包含所有核心复制体成分以及 I 型和 II 型拓扑异构酶的重组酵母复制叉的汇聚。我们发现大多数汇聚的叉在非常晚期停滞，表明需要其他因素的参与。我们表明，Pif1 和 Rrm3 DNA 解旋酶促进了叉的有效汇聚和 DNA 合成的完成，即使在没有 II 型拓扑异构酶的情况下也是如此。此外，Rrm3 和 Pif1 对于体内质粒 DNA 复制的终止也很重要。这些发现确定了一种与先前表征的原核机制不同的真核 DNA 复制终止途径。
