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Conditional mutator gene in Escherichia coli: isolation, mapping, and effector studies.

G E Degnen, E C Cox

    Journal of Bacteriology
    |February 1, 1974
    PubMed
    Summary

    A conditional mutator gene, mutD5, in Escherichia coli significantly increases mutation frequencies. This effect is amplified by thymidine, independent of growth rate, highlighting a novel mechanism of mutagenesis.

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    Area of Science:

    • Microbiology
    • Genetics
    • Molecular Biology

    Background:

    • Mutator genes in bacteria can lead to increased mutation rates.
    • Understanding the mechanisms of mutagenesis is crucial for comprehending bacterial evolution and disease.
    • The Escherichia coli model system is widely used for genetic and molecular studies.

    Purpose of the Study:

    • To identify and characterize a novel conditional mutator gene in Escherichia coli.
    • To investigate the genetic locus and phenotypic expression of the mutD5 mutation.
    • To explore factors influencing the mutD5-induced hypermutation phenotype.

    Main Methods:

    • Isolation and characterization of a conditional mutator mutant (mutD5) in Escherichia coli.
    • P1 transduction to map the mutD5 gene on the bacterial chromosome.
    • Measurement of mutation frequencies for various markers (streptomycin and nalidixic acid resistance) under different media conditions.
    • Assessment of the effect of exogenous thymidine and related compounds on mutation rates.
    • Decoupling of growth rate and mutation rate to isolate the effect of the mutator gene.

    Main Results:

    • The mutD5 gene was mapped to approximately 5.7 minutes on the E. coli chromosome, co-transducing with proA and argF.
    • mutD5 exhibited a conditional mutator phenotype, with mutation frequencies 50-100 times higher than wild-type in both rich and minimal media.
    • Thymidine supplementation (as low as 0.04 muM) significantly elevated mutant frequencies.
    • Other tested compounds like deoxyadenosine, ribonucleosides, thymine, and 2-deoxyribose did not induce similar effects.
    • The observed increase in mutation rate was independent of bacterial growth rate.

    Conclusions:

    • The mutD5 gene represents a novel conditional mutator in Escherichia coli with a significant impact on mutation frequency.
    • Thymidine plays a critical role in potentiating the mutagenic effects of mutD5.
    • The mutD5 mutator phenotype is distinct from growth rate variations, suggesting a specific DNA replication or repair defect.

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