Fasullo Michael T, Sun Mingzeng
College of Nanoscale Sciences and Engineering, SUNY Polytechnic Institute, 257 Fuller Road, Albany, New York 12203, United States.
AIMS Genet. 2017;4(2):84-102. doi: 10.3934/genet.2017.2.84. Epub 2017 Mar 30.
Sister chromatids are preferred substrates for recombinational repair after cells are exposed to DNA damage. While some agents directly cause double-strand breaks (DSBs), others form DNA base adducts which stall or impede the DNA replication fork. We asked which types of DNA damage can stimulate SCE in budding yeast mutants defective in template switch mechanisms and whether PCNA polyubiquitination functions are required for DNA damage-associated SCE after exposure to potent recombinagens. We measured spontaneous and DNA damage-associated unequal sister chromatid exchange (uSCE) in yeast strains containing two fragments of after exposure to MMS, 4-NQO, UV, X rays, and HO endonuclease-induced DSBs. We determined whether other genes in the pathway for template switching, including , , , and were required for DNA damage-associated SCE. was required for DNA damage-associated SCE after exposure to UV, MMS, and 4-NQO, but not for spontaneous, X-ray-associated, or HO endonuclease-induced SCE. While , , and were required for MMS and 4NQO-associated SCE, they were not required for UV-associated SCE. DNA damage-associated recombination between recombination substrates on non-homologous recombination was enhanced in mutants. These results demonstrate that DNA damaging agents that cause DSBs stimulate SCE by -independent mechanisms, while several potent agents that generate bulky DNA adducts stimulate SCE by multiple -dependent mechanisms. We suggest that DSB-associated recombination that occurs in G2 is -independent.
姐妹染色单体是细胞暴露于DNA损伤后重组修复的首选底物。一些试剂直接导致双链断裂（DSB），而其他试剂则形成DNA碱基加合物，从而使DNA复制叉停滞或受阻。我们研究了哪些类型的DNA损伤可以在模板转换机制存在缺陷的芽殖酵母突变体中刺激姐妹染色单体交换（SCE），以及在暴露于强效重组剂后，DNA损伤相关的SCE是否需要增殖细胞核抗原（PCNA）多聚泛素化功能。我们测量了在暴露于甲基磺酸甲酯（MMS）、4-硝基喹啉-1-氧化物（4-NQO）、紫外线（UV）、X射线和HO内切酶诱导的DSB后，含有两个片段的酵母菌株中的自发和DNA损伤相关的不等姐妹染色单体交换（uSCE）。我们确定了模板转换途径中的其他基因，包括 、 、 和 是否是DNA损伤相关SCE所必需的。在暴露于UV、MMS和4-NQO后，DNA损伤相关的SCE需要 ，但自发的、X射线相关的或HO内切酶诱导的SCE则不需要。虽然 、 和 是MMS和4NQO相关SCE所必需的，但UV相关的SCE则不需要它们。在 突变体中，非同源重组上的 重组底物之间的DNA损伤相关重组增强。这些结果表明，导致DSB的DNA损伤剂通过不依赖于 的机制刺激SCE，而几种产生大体积DNA加合物的强效试剂通过多种依赖于 的机制刺激SCE。我们认为，在G2期发生的与DSB相关的重组是不依赖于 的。
