On the mechanism of gene amplification induced under stress in Escherichia coli.
On the mechanism of gene amplification induced under stress in Escherichia coli.
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DOI：
10.1371/journal.pgen.0020048
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发表时间：
2006-04
期刊：
影响因子：
4.5
通讯作者：
Hastings PJ
中科院分区：
文献类型：
--
作者：
Slack A;Thornton PC;Magner DB;Rosenberg SM;Hastings PJ
基因扩增是一个过程的集合，其中一个DNA片段被重复到每个基因组的多个拷贝。它在癌症发生和对化疗药物的耐药性中很重要，并且可以通过扩增基因的表达增加、新基因功能的进化和基因组进化来实现适应性进化。虽然最早在20世纪60年代早期在模式生物大肠杆菌中进行了描述，但关于该系统中扩增机制的信息很少，并且可能建立许多机制模型。最近，大肠杆菌中的一些基因扩增被证明是压力诱导的，并赋予处于压力下的细胞选择优势（适应性扩增），特别是当细胞不适应环境时，可能加速进化。我们专注于大肠杆菌的应激诱导扩增，并报告了一些表明新的分子机制的发现，我们认为大多数扩增可能是应激诱导的，而不是自发的。首先，正如通常假设的那样，用于DNA双链断裂修复和同源重组的某些蛋白质是扩增所必需的。其次，与先前重复序列之间的同源重组导致重复导致扩增的模型不同，扩增的dna以串联形式存在于原位，直接重复7-32千碱基，仅以4至15个富含g的同源碱基对为界，表明初始非同源重组事件。重排连接处的序列表明，在DNA复制过程中，通过模板切换发生的非同源重组机制，但与先前描述的模板切换事件不同，这些必须发生在长距离上。第三，我们提供的证据表明，3 ' -单链DNA末端是该过程的中间产物，支持模板切换机制。第四，我们提供的证据表明，滞后链模板的参与。最后，我们提出了一种新的、远距离的模板切换模型来解释自适应扩增的机制，该模型揭示了应力是如何诱导扩增的。我们概述了它在人类和其他生物体和环境中扩增的可能适用性。所有生物体的基因组都有一个共同的变化，那就是DNA片段重复成多个拷贝。DNA扩增可以通过改变蛋白质的数量来实现快速进化，并且有助于癌症的形成、人类基因组之间的差异以及微生物的抗生素耐药性和致病性。然而，即使是在简单的生物体中，人们对扩增是如何发生的知之甚少。DNA扩增是对压力的反应。在大肠杆菌中，饥饿压力引起扩增，使大肠杆菌最终适应饥饿条件。这项研究阐明了这些应激引起的放大机制的几个方面。这些数据提出了一种新的模式，在这种模式下，DNA复制在饥饿期间停止，新DNA的末端跳到另一个停止复制的分叉上，从而产生一个复制的DNA片段。这种复制可以通过基因重组扩增成许多拷贝。如果这个模型是正确的，就可以解释压力是如何通过阻碍复制来引发这些基因组重排的。一般模型可能对许多生物体中的其他长距离基因组重排有用。压力会导致基因组发生迅速而深刻的变化，其中一些变化会给细胞带来优势——这篇论文有助于解释其中的原理。
Gene amplification is a collection of processes whereby a DNA segment is reiterated to multiple copies per genome. It is important in carcinogenesis and resistance to chemotherapeutic agents, and can underlie adaptive evolution via increased expression of an amplified gene, evolution of new gene functions, and genome evolution. Though first described in the model organism Escherichia coli in the early 1960s, only scant information on the mechanism(s) of amplification in this system has been obtained, and many models for mechanism(s) were possible. More recently, some gene amplifications in E. coli were shown to be stress-inducible and to confer a selective advantage to cells under stress (adaptive amplifications), potentially accelerating evolution specifically when cells are poorly adapted to their environment. We focus on stress-induced amplification in E. coli and report several findings that indicate a novel molecular mechanism, and we suggest that most amplifications might be stress-induced, not spontaneous. First, as often hypothesized, but not shown previously, certain proteins used for DNA double-strand-break repair and homologous recombination are required for amplification. Second, in contrast with previous models in which homologous recombination between repeated sequences caused duplications that lead to amplification, the amplified DNAs are present in situ as tandem, direct repeats of 7–32 kilobases bordered by only 4 to 15 base pairs of G-rich homology, indicating an initial non-homologous recombination event. Sequences at the rearrangement junctions suggest nonhomologous recombination mechanisms that occur via template switching during DNA replication, but unlike previously described template switching events, these must occur over long distances. Third, we provide evidence that 3′-single-strand DNA ends are intermediates in the process, supporting a template-switching mechanism. Fourth, we provide evidence that lagging-strand templates are involved. Finally, we propose a novel, long-distance template-switching model for the mechanism of adaptive amplification that suggests how stress induces the amplifications. We outline its possible applicability to amplification in humans and other organisms and circumstances. A common change in genomes of all organisms is the reiteration of segments of DNA to multiple copies. DNA amplification can allow rapid evolution by changing the amounts of proteins made, and is instrumental in cancer formation, variation between human genomes, and antibiotic resistance and pathogenicity in microbes. Yet little is known about how amplification occurs, even in simple organisms. DNA amplification can occur in response to stress. In Escherichia coli bacteria, starvation stress provokes amplifications that can allow E. coli ultimately to adjust to the starvation condition. This study elucidates several aspects of the mechanism underlying these stress-provoked amplifications. The data suggest a new model in which DNA replication stalls during starvation, and the end of the new DNA jumps to another stalled replication fork to create a duplicated DNA segment. The duplication can then amplify to many copies by genetic recombination. This model, if correct, can explain how stress provokes these genome rearrangements—by replication stalling. The general model may be useful for other long-distance genome rearrangements in many organisms. Stress can cause rapid and profound changes in the genome, some of which can give cells an advantage—this paper helps to explain how.
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影响因子：
56.9
作者：
HARRIS, RS;LONGERICH, S;ROSENBERG, SM
通讯作者：
ROSENBERG, SM
DOI：
10.1073/pnas.92.17.7951
发表时间：
1995-08-15
影响因子：
11.1
作者：
FOSTER, PL;GUDMUNDSSON, G;GOODMAN, MF
通讯作者：
GOODMAN, MF
影响因子：
3.2
作者：
BATES, H;RANDALL, SK;RADMAN, M
通讯作者：
RADMAN, M
影响因子：
56.9
作者：
Gonzalez, E;Kulkarni, H;Ahuja, SK
通讯作者：
Ahuja, SK
DOI：
10.1073/pnas.111008398
发表时间：
2001-07-17
影响因子：
11.1
作者：
Bzymek, M;Lovett, ST
通讯作者：
Lovett, ST