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  • 1
    Electronic Resource
    Electronic Resource
    Double, independent mutational events in the rpsL gene of Escherichia coli: an example of hypermutability? (1993)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 9 (1993), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: A proportion (up to 20%) of newly arising streptomycin-dependent (SmD) colonies of Escherichia coli WP2 contain bacteria where, in addition to a known SmD-determining (primary) mutation in the rpsL gene, there is a further ancillary mutation in the same gene. These ancillary mutations occur at 10 sites between 11 and 201 bp away from the primary mutation. Ancillary mutations have been found in mutant colonies arising both spontaneously and after treatment with ultraviolet light and some have been found repeatedly. Ancillary mutations were frequently found to occur in mixed clones with an excess of bacteria carrying only the primary SmD mutation. No ancillary mutations were found in an adjacent non-coding region and there were no coding sequence changes that did not alter the amino acid specified. Although a selective advantage for bacteria containing ancillary mutations could not be demonstrated directly in every case, some small advantage must be presumed to have occurred to explain the absence of mutations at the other sites and particularly at third (wobble) codon positions. Ancillary mutations appear to occur fairly early in the life of a newly arisen SmD mutant clone in some sort of hypermutable process. Whether they are noticed appears to depend on their conferment of some selective advantage on the bacteria carrying them. While the ancillary mutations within rpsL lie close to, and may be consequent upon the formation of a primary SmD mutation, their mechanism of formation appears to be at least to some extent independent and does not involve the recA or umuC genes. Ancillary mutations were also detected in bacteria lacking reverse transcriptase or transcription repair coupling factor.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1993.tb01694.x
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  • 2
    Electronic Resource
    Electronic Resource
    Radiosensitization of Bacterial and Mammalian Cells by Substituted Glyoxals (1967)
    [s.l.] : Nature Publishing Group
    Nature 216 (1967), S. 137-139 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] Methylglyoxal preferentially sensitizes anoxic bacterial and mammalian cells to the lethal effects of ionizing radiation. The radio-protective effect of anoxia on mammalian cells is effectively abolished in the presence of methylglyoxal, whereas sensitization of oxygenated mammalian cells is ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/216137a0
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  • 3
    Electronic Resource
    Electronic Resource
    mutY 'directs' mutation? (1995)
    [s.l.] : Nature Publishing Group
    Nature 375 (1995), S. 741-741 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] SIR - The ability of cells to undergo spontaneous mutation while in the resting state was demonstrated by Ryan et al.1 with Escherichia coli more than 30 years ago, but received little attention until the report by Cairns and collaborators2 that the mutations that arose were ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/375741a0
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  • 4
    Electronic Resource
    Electronic Resource
    Microbial genetics Hypermutation under stress (1997)
    [s.l.] : Macmillan Magazines Ltd.
    Nature 387 (1997), S. 557-558 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] When a population of microorganisms is unable to grow because nutrients are exhausted or cannot be used, it could make good sense for individuals in that population to experiment with their genomes to try to overcome the deficiency. One approach would be for a subpopulation to start mutating ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/42370
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  • 5
    Electronic Resource
    Electronic Resource
    Untangling ataxia-telangiectasia (1981)
    [s.l.] : Nature Publishing Group
    Nature 289 (1981), S. 222-223 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] THE rare autosomal recessive disorder, ataxia-telangiectasia (AT), has attracted attention because it is associated with an unusual sensitivity to ionizing radiations and an increased susceptibility to cancer, particularly of the lymphoid tissues. Patients also have a variety of other problems, ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/289222a0
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  • 6
    Electronic Resource
    Electronic Resource
    Short term screening tests for carcinogens (1976)
    [s.l.] : Nature Publishing Group
    Nature 261 (1976), S. 195-200 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] There are now short term tests with a high predictive value for mammalian carcinogens. Many of them are based on the ability to detect damage to DNA in bacteria or mammalian cells after metabolic activation by microsomal enzymes. Their introduction will enable provisional safety assessments to be ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/261195a0
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  • 7
    Electronic Resource
    Electronic Resource
    Effect of Sulphydryl Reagents on the Frequency of X-ray-induced Autosomal Recessive Lethal Mutations in Drosophila melanogaster (1964)
    [s.l.] : Nature Publishing Group
    Nature 203 (1964), S. 419-419 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] It was decided to test for enhancement of genetic damage in an organism with structural chromosomes. The induction of autosomal recessive lethals in Drosophila melanogaster males was investigaged by means of the brood analysis technique11, which tests germ cells irradiated at all stages of ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/203419a0
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  • 8
    Electronic Resource
    Electronic Resource
    Segregation of Radiation-Induced Mutations in Escherichia coli (1964)
    [s.l.] : Nature Publishing Group
    Nature 203 (1964), S. 270-272 
    Details
    ISSN: 1476-4687
    Source: Nature Archives 1869 - 2009
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Notes: [Auszug] IT is now accepted1 that the genetic material of bacteria is composed of two main sub-units or strands each of which is conserved during replication. Some years ago Witkin2 reported that with rare exceptions a single nucleus of Escherichia coli contained a single unit of the lac gene mutable by ...
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1038/203270a0
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  • 9
    Electronic Resource
    Electronic Resource
    Mutagenesis in Escherichia coli V. Attempted interconversion of ochre and amber suppressors and mutational instability due to an ochre suppressor (1970)
    Springer
    Molecular genetics and genomics 107 (1970), S. 351-360 
    Details
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A possible quantitative system for the interconversion of ochre and amber suppressors was studied in Escherichia coli WU36-10, a strain in which a leucine requirement is suppressed by amber suppressors and a tyrosine requirement is suppressed by ochre suppressors. The conversion of am Sup-2+ to oc Sup-2+ occurred at rates similar to those for the de novo induction of such suppressors, both spontaneously and after ultraviolet or gamma irradiation. Both induction and conversion of suppressors showed the phenomenon of “mutation frequency decline” after ultraviolet light. Conversions in the opposite direction from oc Sup-2+ to am Sup-2+ were, however, not detected in unmutagenised populations of oc Sup-2+ strains derived either by conversion from an am Sup-2+ strain or de novo from the parental WU36-10, nor were they detected after treatment with ultraviolet light, gamma radiation or 2-aminopurine. If the conversion of oc Sup-2+ to am Sup-2+ occurs at all, it is at a rate very considerably lower than that for the conversion of am Sup-2+ to oc Sup-2+. Some Tyr+ oc Sup-2+ mutants demonstrated mutation rates c. 100 times greater than those of WU36-10 for mutation to Leu+ spontaneously and after ultraviolet or gamma radiation. Possible explanations of this are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00441196
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  • 10
    Electronic Resource
    Electronic Resource
    Mutagenic DNA repair in Escherichia coli. XIV. Influence of two DNA polymerase III mutator alleles on spontaneous and UV mutagenesis (1987)
    Springer
    Molecular genetics and genomics 208 (1987), S. 542-548 
    Details
    ISSN: 1617-4623
    Keywords: DNA polymerase III ; Mutators ; UV mutagenesis ; SOS system ; dnaE mutations ; polC mutations
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary We introduced the dnaE486 and polC74 mutations (which are associated with decreased DNA polymerase III replication fidelity) into excision defective Escherichia coli strains with varying SOS responses. These mutations increased the UV-induced frequency of base pair substitution mutations in all strains tested, except recA430 and umuC122 derivatives. This UV mutator effect therefore requires expression of the SOS error-prone repair system. In recA441 lexA51 strains where the SOS system is constitutively expressed, the UV mutator effect of the dnaE alleles was similar in relative terms (though greater in absolute terms). Since these dnaE alleles decrease rather than increase survival after UV it is argued that they promote a burst of untargeted mutations close to UV photoproducts (“hitch-hiking” mutations) rather than increase the number of translesion synthesis events. The fact that there was no UV mutagenesis in dnaE486 umuC122 or polC74 umuC122 strains indicates that infidelity associated with these dnaE alleles did not of itself enable translesion synthesis to occur. The spontaneous mutator effect conferred by dnaE486 and polC74 was not affected by umuC122 or recA430 indicating that it is not dependent upon error-prone repair ability. In recA441 lexA51 bacteria, where SOS error-prone repair is constitutively induced, the mutator effect of dnaE486 was greater and was largely blocked by umuC122. It is suggested that spontaneously occurring cryptic lesions that are themselves unable to induce the SOS system are subject to translesion synthesis under these conditions and trigger a burst of hitch-hiking mutations that are therefore effectively umuC dependent.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00328153
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