Mechanism of adaptive amplification

遗传变化不仅仅是通过对先前存在的变异的选择而发生的。它也是自适应发生的。这意味着这种变化发生在细胞暴露于选择性环境之后，并且在选择条件下是有利的。细菌的适应性突变过程已经得到了很好的研究，并表明，在一个系统中，是一种独立于自发生长依赖性突变的机制。第二种适应性过程，适应性扩增，最近在这个实验室里在同样的细菌系统中被发现。在适应性扩增中，细胞复制一段DNA的大量拷贝，该DNA携带的基因在更高水平上表达时具有优势。本项目利用DNA测序、基因操作和实验干预等手段，探索大肠杆菌扩增（包括自适应扩增）的分子机制。扩增DNA的结构将被定义，并确定适应性扩增的遗传要求。适应性扩增是否与其他遗传不稳定性有关，如超重组和一般染色体不稳定性，将进行测试。这些结果将有助于确定DNA在环境压力下扩增的机制。在大肠杆菌中扩增的机制目前尚不清楚。这项工作的结果将为在压力下细胞中的DNA交易提供新的见解，也为染色体不稳定的一般过程，以及细胞对压力环境的适应提供新的见解。这项研究的结果将与许多在压力下发生遗传变化的情况有关。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。最近发现的多种不同的DNA修复过程在细菌和人类之间高度保守，以及在不易处理的人体系统中缺乏机制信息，强调了这项工作与人类健康的许多方面的相关性。

Genetic change occurs not only by selection of preexisting variation. It also occurs adaptively. This means that the change occurs after cells are exposed to a selective environment, and is advantageous under the conditions of selection. The process of adaptive mutation in bacteria has been well studied and shown, in one system, to be a separate mechanism from spontaneous growth-dependent mutation. A second adaptive process, adaptive amplification, was recently discovered in this laboratory in the same bacterial system. In adaptive amplification, the cell makes numerous copies of a length of DNA carrying a gene that confers an advantage when expressed at a higher level. This project explores the molecular mechanism of amplification (including adaptive amplification) in Escherichia coli, using DNA sequencing, genetic manipulation and experimental intervention. The structure of amplified DNA will be defined, and the genetic requirements for adaptive amplification determined. Whether adaptive amplification is associated with other genetic instability, such as hyper-recombination and general chromosomal instability, will be tested. These results will help to define a mechanism by which DNA is amplified in response to environmental stress. The mechanism of amplification in E. coli is poorly understood at present. The results of this work will provide new insights into DNA transactions in cells under stress, and also to the general processes of chromosomal instability, and adaptation of cells to stressed environments. 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. The recent discoveries of multiple different 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 many aspects of human health.