RADIATION INDUCTION OF GENOMIC REARRANGEMENTS IN YEAST

DNA损伤会产生重组双链断裂， 损伤诱导基因（DIN基因）的表达，并阻止细胞 在明确定义的细胞周期检查点循环。基因组的存在 白血病和淋巴瘤中的重排，以及 电离辐射暴露和急性放射性损伤频率升高 白血病，需要更好地了解重组剂如何 刺激染色体间重排。总体目标是 了解重组损伤如何修复， 保持完整性。这项提议研究损伤诱导反应 在酿酒酵母（酵母），首先集中在遗传 调节损伤诱导的有丝分裂重组发生在 分散的重复DNA序列（异位重组）。结果 在这些研究中获得的结果可能支持四个重要的假设， 所有生物体中的基因组稳定性：1） 重组酶与有丝分裂的发生率增加相关， 2）错配修复系统在流产中很重要， 不同序列之间的重组中间体， 重组原可能绕过这种控制，3）拓扑异构酶和 解旋酶在将重组中间体引导到 不产生染色体重排的途径，和4） 在确定的细胞周期检查点的细胞周期停滞是必要的， 这些机制发挥作用。第一个目标是使用his 3重组 定量辐射修复中突变效应的底物， 错配修复，拓扑异构酶，损伤诱导的姐妹染色单体 重组和细胞周期的控制对自发和 损伤诱导的染色体间重组。第二个目标决定了 是否增强了辐射诱导基因的表达， RAD 51基因与重组增加相关。第三个目标是 构建重组底物， 在任何两个相同的DNA重复序列之间发生的重组可以是 定量;将这些底物置于非同源染色体上 这样就可以测量易位。重复的序列， 研究包括δ元素发生在酵母的末端 反转录转座子Ty 1和Alu序列约300 bp序列 在酵母上克隆的人类DNA中平均每6 kb出现一次 人工染色体（YACs）。然后，将进行纯化分析， 不相同重复序列之间的有丝分裂、异位重组是否可以 会受到DNA损伤剂的刺激第四个目标是确定 错配修复途径中的突变体是否表现出更高的频率 这些序列之间的重组，以及是否过度表达 RAD 51重组酶将增强这些重复序列之间重组。 这项研究的结果将有助于了解遗传控制的 在酵母中的基因组稳定性，有利于外源DNA的维持 在YAC上引入酵母，并提供对 真核系统中DNA损伤剂的重组原性。在 此外，为酵母设计的新型重组底物将是 对有兴趣创造类似重组的遗传学家来说， 高等真核生物的底物。

DNA damage generates recombinogenic double-strand breaks, induces the expression of damage-inducible genes (DIN genes), and arrests the cell cycle at well defined cell-cycle checkpoints. The presence of genomic rearrangements in leukemias and lymphomas, and the correlation between exposure to ionizing radiation and the elevated frequencies of acute leukemia, require a better understanding of how recombinogenic agents can stimulate interchromosomal rearrangements. The general goal is to understand how recombinogenic lesions are repaired so that genomic integrity is maintained. This proposal studies damage-inducible responses in Saccharomyces cerevisae (yeast) by first focusing on the genetic regulation of damage-induced mitotic recombination occurring between dispersed repeated DNA sequences (ectopic recombination). The results obtained in these studies may support four important hypotheses concerning genomic stability in all organisms: 1) that elevated levels of recombinases are correlated with the increased incidence of mitotic rearrangements, 2) that mismatch repair systems are important in aborting recombinational intermediates between divergent sequences and recombinogens may circumvent this control, 3) that topoisomerases and helicases are important in channelling recombinational intermediates into a pathway that does not generate chromosomal rearrangements, and 4) that cell cycle arrest at defined cell cycle checkpoints is necessary to allow these mechanisms to act. The first aim uses the his3 recombinational substrates to quantitate effects of mutations in radiation repair, mismatch repair, topoisomerases, damage-induced sister chromatid recombination and cell cycle control on the rates of spontaneous and damage-induced interchromosomal recombination. The second aim determines whether enhanced expression of radiation-inducible genes, including the RAD51 gene, is correlated with elevated recombination. The third aim is to construct recombinational substrates so that the frequencies of ectopic recombination occurring between any two identical DNA repeats can be quantitated; these substrates will be placed on non-homologous chromosomes so that translocations can be measured. Repeated sequences that will be studied include delta elements occurring at the end of the yeast retrotransposon Ty1 and Alu sequences approximately 300 bp sequence occurring once every 6 kb on average in human DNA cloned on yeast artificial chromosomes (YACs). Recombination assays will then determine whether mitotic, ectopic recombination between non-identical repeats can be stimulated by DNA damaging agents. The fourth aim is to determine whether mutants in the mismatch repair pathways exhibit higher frequencies of recombination between these sequences and whether over-expression of the RAD51 recombinase will enhance recombination between these repeats. Results from this study will aid in understanding the genetic control of genomic stability in yeast, facilitate the maintenance of foreign DNA introduced in yeast on YACs, and provide insights into the recombinogenicity of DNA damaging agents in eukaryotic systems. In addition, the novel recombinational substrates designed for yeast will be of benefit to geneticists interested in creating similar recombinational substrates for higher eukaryotes.