RADIATION INDUCTION OF GENOMIC REARRANGEMENTS IN YEAST

DNA损伤诱导的细胞周期检查点已被假定为是重要的，在维持遗传稳定性，通过阻止或延迟细胞周期，以便有时间修复重组DNA损伤。 已经在癌细胞中观察到取消检查点并增加遗传不稳定性的功能丧失突变，并且可能导致快速增殖和/或对化疗药物和放射疗法的抗性。 细胞周期检查点基因可以在信号转导途径中起作用，其中DNA损伤的存在被传递到细胞周期机制和转录装置以上调DNA修复基因。 本提案的目的是阐明酿酒酵母RAD 9检查点降低重复序列之间同源重组（异位重组）导致的遗传不稳定性的遗传途径。 我们以前已经描述了一种染色体易位试验，可以测量酵母rad 9突变体的遗传不稳定性。 第一个目的是鉴定在RAD 9介导的信号转导途径中减少辐射相关的易位刺激的特定基因或基因组合。 第二个目的是研究其他细胞周期检查点在维持遗传稳定性方面的贡献。 第三个目的是了解检查点是否也减少了酵母Ty元件之间的辐射相关重组。 本研究中获得的结果也可以阐明当前关于真核生物中基因组稳定性的观点：1）重组酶水平的升高在DNA复制产生的双链断裂（DSB）的DNA修复中可能是重要的，2）触发G2-M检查点和控制遗传稳定性的信号转导途径是多余的，3）在检查点突变体中观察到的遗传变化的非随机积累可能部分由反转录转座子之间的重组引起。

DNA damage-induced cell cycle checkpoints have been postulated to be important in maintaining genetic stability by arresting or delaying the cell cycle to allow time for repair of recombinogenic DNA damage. Loss-of-function mutations that abolish checkpoints and increase genetic instability have been observed in cancer cells and may contribute to rapid proliferation and/or resistance to chemotherapeutic drugs and radiation therapy. Cell cycle checkpoint genes may function in a signal transduction pathway in which the presence of DNA damage is relayed to both the cell cycle machinery and the transcription apparatus to upregulate DNA repair genes. The purpose of this proposal is to elucidate the genetic pathway by which the Saccharomyces cerevisiae RAD9 checkpoint reduces genetic instability that results from homologous recombination between repeated sequences (ectopic recombination). We have previously described a chromosomal translocation assay that can measure genetic instability in yeast rad9 mutants. The first aim is to identify specific genes or combinations of genes in the RAD9- mediated signal transduction pathway which reduce the radiation- associated stimulation of translocations. The second aim is to examine the contribution of other cell cycle checkpoints in maintaining genetic stability. The third aim is to understand whether checkpoints also reduce the radiation-associated recombination between yeast Ty elements. The results obtained in this study may also elucidate current ideas concerning genomic stability in eukaryotic organisms: 1) that elevated levels of recombinases may be important in DNA repair of double-strand breaks (DSBs) generated by DNA replication, 2) that signal transduction pathways that trigger the G2-M checkpoint and control genetic stability are redundant, 3) that the non-random accumulation of genetic changes observed in checkpoint mutants may partially result from recombination between retrotransposons.