英国MRC分子生物学实验室Lori A. Passmore等研究人员合作发现，FANCD2-FANCI检测DNA并识别双链到单链连接点。相关论文于2024年7月31日在线发表在《自然》杂志上。

研究人员表示，DNA交联会阻碍DNA复制，并通过Fanconi贫血通路修复。FANCD2–FANCI（D2–I）蛋白复合体在这一过程中发挥核心作用，因为它通过协调DNA损伤周围的切割来启动修复。然而，D2–I还在DNA修复中发挥更广泛的作用，保护停滞的复制叉免受非计划降解的影响。当前尚不清楚DNA交联是如何被识别的，以及D2–I在复制叉保护中的作用机制。

研究人员利用单分子成像技术展示了D2–I作为滑动夹克的功能，它能够结合并在双链DNA上扩散。特别的是，滑动中的D2–I在遇到单链–双链（ss–ds）DNA连接结构时会停滞，这种结构是在复制叉在DNA损伤处停滞时产生的。通过冷冻电镜技术，研究人员确定了D2–I在DNA上的结构，显示停滞的D2–I与ss–dsDNA连接的特定相互作用，这些相互作用与滑动中的D2–I有所不同。

因此，D2–I在双链DNA上巡视，当它遇到ssDNA缺口时，会特异性地夹在ss–dsDNA连接处。由于ss–dsDNA连接处存在于停滞的复制叉上，D2–I能够识别DNA损伤位点。这些数据提供了一个统一的分子机制，调和了D2–I在多个DNA修复途径中识别和保护停滞复制叉的角色。

附：英文原文

Title: FANCD2–FANCI surveys DNA and recognizes double- to single-stranded junctions

Author: Alcn, Pablo, Kaczmarczyk, Artur P., Ray, Korak Kumar, Liolios, Themistoklis, Guilbaud, Guillaume, Sijacki, Tamara, Shen, Yichao, McLaughlin, Stephen H., Sale, Julian E., Knipscheer, Puck, Rueda, David S., Passmore, Lori A.

Issue&Volume: 2024-07-31

Abstract: DNA crosslinks block DNA replication and are repaired by the Fanconi anaemia pathway. The FANCD2–FANCI (D2–I) protein complex is central to this process as it initiates repair by coordinating DNA incisions around the lesion1. However, D2–I is also known to have a more general role in DNA repair and in protecting stalled replication forks from unscheduled degradation2,3,4. At present, it is unclear how DNA crosslinks are recognized and how D2–I functions in replication fork protection. Here, using single-molecule imaging, we show that D2–I is a sliding clamp that binds to and diffuses on double-stranded DNA. Notably, sliding D2–I stalls on encountering single-stranded–double-stranded (ss–ds) DNA junctions, structures that are generated when replication forks stall at DNA lesions5. Using cryogenic electron microscopy, we determined structures of D2–I on DNA that show that stalled D2–I makes specific interactions with the ss–dsDNA junction that are distinct from those made by sliding D2–I. Thus, D2–I surveys dsDNA and, when it reaches an ssDNA gap, it specifically clamps onto ss–dsDNA junctions. Because ss–dsDNA junctions are found at stalled replication forks, D2–I can identify sites of DNA damage. Therefore, our data provide a unified molecular mechanism that reconciles the roles of D2–I in the recognition and protection of stalled replication forks in several DNA repair pathways.

DOI: 10.1038/s41586-024-07770-w

Source: https://www.nature.com/articles/s41586-024-07770-w