Weill Cornell Medicine, Department of Pathology and Laboratory Medicine, New York, NY 10065, USA.
Graduate Institute of Natural Products, Chang Gung University, Taoyuan 333, Taiwan.
Mol Cell. 2018 Mar 1;69(5):879-892.e5. doi: 10.1016/j.molcel.2018.01.031. Epub 2018 Feb 22.
The access-repair-restore model for the role of chromatin in DNA repair infers that chromatin is a mere obstacle to DNA repair. However, here we show that blocking chromatin assembly, via knockdown of the histone chaperones ASF1 or CAF-1 or a mutation that prevents ASF1A binding to histones, hinders Rad51 loading onto ssDNA during homologous recombination. This is a consequence of reduced recruitment of the Rad51 loader MMS22L-TONSL to ssDNA, resulting in persistent RPA foci, extensive DNA end resection, persistent activation of the ATR-Chk1 pathway, and cell cycle arrest. In agreement, histones occupy ssDNA during DNA repair in yeast. We also uncovered DNA-PKcs-dependent DNA damage-induced ASF1A phosphorylation, which enhances chromatin assembly, promoting MMS22L-TONSL recruitment and, hence, Rad51 loading. We propose that transient assembly of newly synthesized histones onto ssDNA serves to recruit MMS22L-TONSL to efficiently form the Rad51 nucleofilament for strand invasion, suggesting an active role of chromatin assembly in homologous recombination.
染色质在 DNA 修复中的作用的访问-修复-恢复模型推断染色质仅仅是 DNA 修复的障碍。然而，在这里，我们表明，通过敲低组蛋白伴侣 ASF1 或 CAF-1，或阻止 ASF1A 与组蛋白结合的突变，阻断染色质组装，会阻碍同源重组过程中 Rad51 加载到 ssDNA 上。这是由于 Rad51 加载器 MMS22L-TONSL 向 ssDNA 的募集减少，导致持续的 RPA 焦点、广泛的 DNA 末端切除、持续激活 ATR-Chk1 途径和细胞周期停滞的结果。一致地，在酵母中，组蛋白在 DNA 修复过程中占据 ssDNA。我们还发现了 DNA-PKcs 依赖性的 DNA 损伤诱导的 ASF1A 磷酸化，它增强了染色质组装，促进了 MMS22L-TONSL 的募集，从而促进了 Rad51 的加载。我们提出，新合成的组蛋白在 ssDNA 上的短暂组装用于招募 MMS22L-TONSL，以有效地形成 Rad51 核丝进行链入侵，这表明染色质组装在同源重组中具有积极作用。
