Genetic Analysis of Bacterial Chromosome Structure

这项申请提出了一个调查的过程中，基因复制和扩增进一步 在选择下生长。我们用这个过程来解释“适应性突变”现象 并且已经表明，选择性应激实际上不是诱变的（如所声称的），而是因为 选择有利于具有通过复制形成的限速基因的额外拷贝的细胞生长， 放大选择通过增加突变目标的数量来提高突变体的频率 并且可以在不改变突变率的情况下完成。我们的模型对所有遗传系统都是通用的，并导致 一个非常强大的遗传适应过程嵌套的连续克隆扩张。这个过程是 与癌症的起源和病原体对宿主的适应高度相关-两种情况， 单细胞群体在疾病过程中进行遗传适应。基因扩增证明了 对癌症的发展和对癌症化疗的抗性很重要。我们建议 这里采用的方法是重要的，因为它研究了重组机制之间的界面， 和种群生物学。我们将描述两个细菌系统（除了凯恩斯的）， 使用（错误地，我们认为）支持压力诱导诱变的想法。我们的希望是揭示新的 遗传适应机制，并解决围绕“适应性突变”的争议。到目前为止， 我们已经了解到，扩增在选择下的生长过程中被重塑，以缩短其重复单位， 增加它们的拷贝数。我们发现了一种新的放大形式（反向复制）， 将测试一个模型，这些recruments如何产生和改造下的选择。新的重组- 独立的分析表明RecA不是复制形成所必需的;这项分析应该有助于 描述复制的功能需求。我们发现复制的可逆性 导致它们在种群中的频率接近稳定状态水平。重复的隔离 提供了一种内部重组的检测方法，这种方法确实提供了DNA末端（就像有性交换一样）， 依赖于引发结构的自发产生。因此，本试验允许研究自发性 启动重组的事件。我们开发了一种重复分离率的检测方法， 增长率的问题，并表明回文序列刺激重复的形成。

This application proposes an investigation of the processes by which genes duplicate and amplify further during growth under selection. We've applied this process to explain the phenomenon of "adaptive mutation" and have shown that selective stress is not actually mutagenic (as claimed) but appears so because selection favors growth of cells with additional copies of the rate-limiting gene formed by duplication and amplification. Selection enhances the frequency of mutants by increasing the number of mutation targets and can do so with no change in the mutation rate. Our model is general for all genetic systems and leads to an extremely powerful process for genetic adaptation - nested serial clonal expansions. This process is highly relevant to the origins of cancer and adaptation of pathogens to hosts - two situations in which populations of single cells adapt genetically during the course of a disease. Gene amplifications are proving important to development of cancer and resistance to cancer chemotherapies. We suggest that the approach taken here is important because it investigates the interface between recombination mechanism and population biology. We will characterize two bacterial systems (in addition to Cairns') that have been used (incorrectly, we believe) to support the idea of stress-induced mutagenesis. Our hope is to reveal new mechanisms of genetic adaptation and to resolve the controversy surrounding "adaptive mutation". Thus far, we've learned that amplifications are remodeled during growth under selection to shorten their repeated unit and increase their copy number. We've discovered a new form of amplification (inversion-duplication) and will test a model for how these rearrangments arise and remodel under selection. A new recombination- independent assay shows that RecA is not essential for duplication formation; this assay should help characterize the functional requirements of duplication. We've found that the reversibiltiy of duplications causes their frequency in a population to approach a steady state level. The segregation of duplications provides an assay for internal recombination that does supply DNA ends (as does sexual exchange) but relies on spontaneous production of initiating structures. Therefore this assay allows study of spontaneous events that initiate recombination. We've developed an assay for duplication segregation rate that avoids growth rate problems and shows that palindromic sequence stimulate duplication formation.