Laboratory of Genome Regeneration, Institute of Molecular and Cellular Biosciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
Laboratory of Genome Regeneration, Institute of Molecular and Cellular Biosciences, University of Tokyo, 1-1-1 Yayoi, Bunkyo-ku, Tokyo 113-0032, Japan.
Mol Cell. 2017 May 18;66(4):533-545.e5. doi: 10.1016/j.molcel.2017.04.020.
Arrested replication forks lead to DNA double-strand breaks (DSBs), which are a major source of genome rearrangements. Yet DSB repair in the context of broken forks remains poorly understood. Here we demonstrate that DSBs that are formed at arrested forks in the budding yeast ribosomal RNA gene (rDNA) locus are normally repaired by pathways dependent on the Mre11-Rad50-Xrs2 complex but independent of HR. HR is also dispensable for DSB repair at stalled forks at tRNA genes. In contrast, in cells lacking the core replisome component Ctf4, DSBs are formed more frequently, and these DSBs undergo end resection and HR-mediated repair that is prone to rDNA hyper-amplification; this highlights Ctf4 as a key regulator of DSB end resection at arrested forks. End resection also occurs during physiological rDNA amplification even in the presence of Ctf4. Suppression of end resection is thus important for protecting DSBs at arrested forks from chromosome rearrangements.
停滞的复制叉会导致 DNA 双链断裂（DSB），这是基因组重排的主要来源。然而，在断裂叉的背景下，DSB 的修复仍然知之甚少。在这里，我们证明在芽殖酵母核糖体 RNA 基因（rDNA）位点的停滞叉形成的 DSB 通过依赖于 Mre11-Rad50-Xrs2 复合物但不依赖于 HR 的途径正常修复。HR 对于 tRNA 基因中停滞叉的 DSB 修复也是可有可无的。相比之下，在缺乏核心复制体成分 Ctf4 的细胞中，DSB 的形成更为频繁，这些 DSB 经历末端切除和 HR 介导的修复，容易导致 rDNA 过度扩增；这凸显了 Ctf4 作为停滞叉处 DSB 末端切除的关键调节剂的作用。即使存在 Ctf4，末端切除也会在生理 rDNA 扩增过程中发生。因此，抑制末端切除对于保护停滞叉处的 DSB 免受染色体重排至关重要。
