Protein and Nucleic Acid Chemistry Division, Medical Research Council, Laboratory of Molecular Biology, Cambridge CB2 0QH, UK.
Protein and Nucleic Acid Chemistry Division, Medical Research Council, Laboratory of Molecular Biology, Cambridge CB2 0QH, UK.
Mol Cell. 2024 Sep 19;84(18):3469-3481.e7. doi: 10.1016/j.molcel.2024.08.004. Epub 2024 Sep 4.
Topoisomerase 1 cleavage complexes (Top1-ccs) comprise a DNA-protein crosslink and a single-stranded DNA break that can significantly impact the DNA replication machinery (replisome). Consequently, inhibitors that trap Top1-ccs are used extensively in research and clinical settings to generate DNA replication stress, yet how the replisome responds upon collision with a Top1-cc remains obscure. By reconstituting collisions between budding yeast replisomes, assembled from purified proteins, and site-specific Top1-ccs, we have uncovered mechanisms underlying replication fork stalling and collapse. We find that stalled replication forks are surprisingly stable and that their stability is influenced by the template strand that Top1 is crosslinked to, the fork protection complex proteins Tof1-Csm3 (human TIMELESS-TIPIN), and the convergence of replication forks. Moreover, nascent-strand mapping and cryoelectron microscopy (cryo-EM) of stalled forks establishes replisome remodeling as a key factor in the initial response to Top1-ccs. These findings have important implications for the use of Top1 inhibitors in research and in the clinic.
拓扑异构酶 1 断裂复合物(Top1-ccs)包含一个 DNA-蛋白质交联和一个单链 DNA 断裂,这可能会严重影响 DNA 复制机制(复制体)。因此,广泛地在研究和临床环境中使用捕获 Top1-ccs 的抑制剂来产生 DNA 复制应激,然而复制体在与 Top1-ccs 碰撞时的反应仍然不清楚。通过重新组装从纯化蛋白组装的芽殖酵母复制体与定点 Top1-ccs 之间的碰撞,我们揭示了复制叉停滞和崩溃的机制。我们发现停滞的复制叉出人意料地稳定,并且它们的稳定性受到 Top1 交联的模板链、叉保护复合物蛋白 Tof1-Csm3(人类 TIMELISSTIPIN)以及复制叉的汇聚的影响。此外,新生链映射和停滞叉的冷冻电镜(cryo-EM)确定了复制体重塑是对 Top1-ccs 初始反应的关键因素。这些发现对 Top1 抑制剂在研究和临床中的应用具有重要意义。