In Eukarya and Archaea, the lagging strand synthesis is accomplished mainly by three key factors, DNA polymerase (Pol), flap endonuclease (FEN), and DNA ligase (Lig), in the DNA replication process. These three factors form important complexes with proliferating cell nuclear antigen (PCNA), thereby constructing a platform that enable each protein factor to act successively and smoothly on DNA. The structures of the Pol-PCNA-DNA and Lig-PCNA-DNA complexes alone have been visualized by single particle analysis. However, the FEN-PCNA-DNA complex structure remains unknown. In this report, we for the first time present this tertiary structure determined by single particle analysis. We also successfully visualized the structure of the FEN-Lig-PCNA-DNA complex, corresponding to a putative intermediate state between the removal of the DNA flap by FEN and the sealing of the nicked DNA by Lig. This structural study presents the direct visualization of the handing-over action, which proceeds between different replication factors on a single PCNA clamp bound to DNA. We detected a drastic conversion of the DNA from a bent form to a straight form, in addition to the dynamic motions of replication factors in the switching process.

中文翻译：

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DNA警棒在与PCNA结合的复制因子之间通过的直接可视化。

在Eukarya和Archaea中，滞后链的合成主要由三个关键因素完成，即DNA复制过程中的DNA聚合酶（Pol），襟翼内切核酸酶（FEN）和DNA连接酶（Lig）。这三个因素与增殖细胞核抗原（PCNA）形成重要的复合物，从而构建了一个平台，使每种蛋白质因子都能连续，平稳地作用于DNA。单独的Pol-PCNA-DNA和Lig-PCNA-DNA复合物的结构已通过单颗粒分析实现了可视化。但是，FEN-PCNA-DNA复合物的结构仍然未知。在本报告中，我们首次介绍了通过单颗粒分析确定的三级结构。我们还成功地可视化了FEN-Lig-PCNA-DNA复合物的结构，对应于通过FEN去除DNA瓣和用Lig密封带切口的DNA之间的假定的中间状态。这项结构研究提供了移交动作的直接可视化，移交动作在绑定到DNA的单个PCNA夹具上的不同复制因子之间进行。除了在切换过程中复制因子的动态运动之外，我们还检测到了DNA从弯曲形式到笔直形式的急剧转变。