Tsabar Michael, Hicks Wade M, Tsaponina Olga, Haber James E
Department of Biology and Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, MA 02454-9110, United States.
Department of Biology and Rosenstiel Basic Medical Sciences Research Center, Brandeis University, Waltham, MA 02454-9110, United States.
DNA Repair (Amst). 2016 Nov;47:21-29. doi: 10.1016/j.dnarep.2016.09.005. Epub 2016 Sep 28.
Homologous recombination (HR) is an evolutionarily conserved pathway in eukaryotes that repairs a double-strand break (DSB) by copying homologous sequences from a sister chromatid, a homologous chromosome or an ectopic location. Recombination is challenged by the packaging of DNA into nucleosomes, which may impair the process at many steps, from resection of the DSB ends to the re-establishement of nucleosomes after repair. However, nucleosome dynamics during DSB repair have not been well described, primarily because of a lack of well-ordered nucleosomes around a DSB. We designed a system in budding yeast Saccharomyces cerevisiae to monitor nucleosome dynamics during repair of an HO endonuclease-induced DSB. Nucleosome occupancy around the break is lost following DSB formation, by 5'-3' resection of the DSB end. Soon after repair is complete, nucleosome occupancy is partially restored in a repair-dependent but cell cycle-independent manner. Full re-establishment of nucleosome protection back to the level prior to DSB induction is achieved when the cell cycle resumes following repair. These findings may have implications to the mechanisms by which cells sense the completion of repair.
同源重组（HR）是真核生物中一种进化上保守的途径，它通过从姐妹染色单体、同源染色体或异位位置复制同源序列来修复双链断裂（DSB）。DNA包装成核小体会对重组产生挑战，这可能会在从DSB末端切除到修复后核小体重新建立的许多步骤中损害该过程。然而，DSB修复过程中的核小体动态变化尚未得到很好的描述，主要是因为DSB周围缺乏有序排列的核小体。我们在芽殖酵母酿酒酵母中设计了一个系统，以监测HO内切酶诱导的DSB修复过程中的核小体动态变化。DSB形成后，通过DSB末端的5'-3'切除，断裂周围的核小体占有率丧失。修复完成后不久，核小体占有率以依赖于修复但不依赖于细胞周期的方式部分恢复。当修复后细胞周期恢复时，核小体保护完全恢复到DSB诱导前的水平。这些发现可能对细胞感知修复完成的机制有影响。
