Article

The σE stress response is required for stress‐induced mutation and amplification in Escherichia coli

Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, TX 77030-3411, USA.
Molecular Microbiology (Impact Factor: 5.03). 05/2010; 77(2):415-30. DOI: 10.1111/j.1365-2958.2010.07213.x
Source: PubMed

ABSTRACT Pathways of mutagenesis are induced in microbes under adverse conditions controlled by stress responses. Control of mutagenesis by stress responses may accelerate evolution specifically when cells are maladapted to their environments, i.e. are stressed. Stress-induced mutagenesis in the Escherichia coli Lac assay occurs either by 'point' mutation or gene amplification. Point mutagenesis is associated with DNA double-strand-break (DSB) repair and requires DinB error-prone DNA polymerase and the SOS DNA-damage- and RpoS general-stress responses. We report that the RpoE envelope-protein-stress response is also required. In a screen for mutagenesis-defective mutants, we isolated a transposon insertion in the rpoE P2 promoter. The insertion prevents rpoE induction during stress, but leaves constitutive expression intact, and allows cell viability. rpoE insertion and suppressed null mutants display reduced point mutagenesis and maintenance of amplified DNA. Furthermore, sigma(E) acts independently of stress responses previously implicated: SOS/DinB and RpoS, and of sigma(32), which was postulated to affect mutagenesis. I-SceI-induced DSBs alleviated much of the rpoE phenotype, implying that sigma(E) promoted DSB formation. Thus, a third stress response and stress input regulate DSB-repair-associated stress-induced mutagenesis. This provides the first report of mutagenesis promoted by sigma(E), and implies that extracytoplasmic stressors may affect genome integrity and, potentially, the ability to evolve.

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Available from: Christophe Herman, Aug 29, 2015
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    • "We find, as shown in Figure 1C, that RpoS level changes regulation of both repair systems simultaneously , so both together contribute to SIM, even though different networks regulate the two processes (Al Mamun et al. 2012; Gutierrez et al. 2013). For example, other influences besides RpoS (such as from RpoE;Gibson et al. 2010) may additionally affect the overall mutation rate. Nevertheless , the mutation rate threshold in Figure 1 is correlated with the regulation of mutS and dinB in the strains set. "
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    ABSTRACT: Evolutionary innovations are dependent on mutations. Mutation rates are increased by adverse conditions in the laboratory but there is no evidence that stressful environments that do not directly impact on DNA leave a mutational imprint on extant genomes. Mutational spectra in the laboratory are normally determined with unstressed cells but are unavailable with stressed bacteria. To by-pass problems with viability, selection effects and growth rate differences due to stressful environments, in this study we used a set of genetically engineered strains to identify the mutational spectrum associated with nutritional stress. The strain set members each had a fixed level of the master regulator protein, RpoS, which controls the general stress response of Escherichia coli. By assessing mutations in cycA gene from 485 cycloserine resistant mutants collected from as many as independent cultures with three distinct perceived stress (RpoS) levels, we were able establish a dose-dependent relationship between stress and mutational spectra. The altered mutational patterns included base pair substitutions, single base pair indels, longer indels and transpositions of different insertion sequences. The mutational spectrum of low-RpoS cells closely matches the genome-wide spectrum previously generated in laboratory environments, while the spectra of high-RpoS, high perceived stress cells more closely matches spectra found in comparisons of extant genomes. Our results offer an explanation of the uneven mutational profiles such as the transition-transversion biases observed in extant genomes and provide a framework for assessing the contribution of stress-induced mutagenesis to evolutionary transitions and the mutational emergence of antibiotic resistance and disease states.
    Molecular Biology and Evolution 11/2014; 32(2). DOI:10.1093/molbev/msu306 · 14.31 Impact Factor
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    • "Repair of DSBs by HR in E. coli is non-mutagenic in unstressed cells, but under stress, switches to a mutagenic mode that is activated by stress responses (Ponder et al., 2005; Shee et al., 2011). This mutagenic repair of DNA breaks requires proteins that mend DSBs by HR, error-prone DNA polymerases, activation of SOS DDR, the controlled general and starvation stress response (RpoS), and a membrane protein stress response (RpoE), that promotes spontaneous DNA breakage in some DNA regions (Gibson et al., 2010). RpoS controls the switch that changes the normally high-fidelity process of DSBR via HR to an error-prone one. "
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    Frontiers in Genetics 06/2014; 5:175. DOI:10.3389/fgene.2014.00175
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    • "We also identified CDSs for the subunits of the RNA polymerase RpoA, RpoB, RpoC, and a member of the extracytoplasmic function (ECF) subfamily RpoE. The latter responds to signals from the external environment, presence of misfolded proteins and heat/oxidative stress in other bacteria [41-44] and presumably performs similar functions for M. haemofelis. "
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