Mechanisms of Adaptive Amplification

描述（由申请方提供）：强制降解细胞发生许多生理变化，使其能够耐受这些条件。现在越来越清楚的是，它们也经历遗传变化，并且作为压力反应的一部分，遗传变化的速度加快。这种由压力引起的基因变化过程被称为适应性突变。细菌的适应性点突变过程已经得到了很好的研究，并显示出与生长依赖性突变不同。在另一个适应性过程中，适应性基因扩增，细胞产生携带基因的DNA长度的许多拷贝，该基因在高水平表达时是有利的。该项目研究了大肠杆菌适应性扩增的分子机制，测试了扩增的起始事件是复制叉停止的假设，当它们重新启动时，复制了错误的模板，从而复制了一段基因组。遗传和分子操作被用来探索这一假设，并了解在停滞的复制叉发生的事件。只有当细胞表达控制细胞一般应激反应的因子时，适应性扩增才会发生。这允许通过研究哪些应激反应的组分需要扩增来调查细胞响应于应激而诱导这些遗传变化的事件。这项研究的结果将与压力下发生遗传变化的许多情况有关。这些包括致病性的进化、病原体和肿瘤细胞中耐药性的发展以及肿瘤的发展。复制叉停滞也与重复不稳定性相关遗传疾病的基础过程有关。在细菌和人类之间高度保守的多个DNA修复过程的发现，以及在不太容易处理的人类系统中缺乏机械信息，强调了这项工作与人类健康的许多方面的相关性。

DESCRIPTION (provided by applicant): Stressed cells undergo many physiological changes that allow them to tolerate the conditions. It is now becoming clear that they also undergo genetic change, and that the rate of genetic change is accelerated as a part of the stress-response. This process of stress-induced genetic change is called adaptive mutation. The processes of adaptive point mutation in bacteria have been well studied and shown to be distinct from growth-dependent mutation. In another adaptive process, adaptive gene amplification, the cell makes many copies of a length of DNA carrying a gene that is advantageous when expressed at a high level. This project investigates the molecular mechanism of adaptive amplificiation in Escherichia coli, testing the hypothesis that the initiating event of amplification is that replication forks stall and that, when they restart, the wrong template is copied, thus duplicating a length of the genome. Genetic and molecular manipulation is used to explore this hypothesis and to learn about the events occurring at stalled replication forks. Adaptive amplification only occurs if the cells are expressing the factors that control the cell's general stress response. This allows investigation of the events by which a cell induces these genetic changes in response to stress by studying which components of stress responses are needed for amplification. The results of this study will be relevant to many situations in which genetic change occurs under stress. These include the evolution of pathogenicity, the development of drug resistance in pathogens and in tumor cells, and the development of tumors. Replication fork stalling is also relevant to the processes that underlie repeat instability-related genetic diseases. The discoveries of multiple DNA repair process that are highly conserved between bacteria and humans, and the paucity of mechanistic information in the less tractable human system, underscore the relevance of this work to may aspects of human health.