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The role of pre-replication and post-replication processes in mutation induction in Haemophilus influenzae by

R F Kimball, S W Perdue, M E Boling

    Mutation Research
    |October 1, 1978
    PubMed

    Insights

    This study investigated DNA repair and mutation fixation in Haemophilus influenzae after N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) exposure. Results indicate DNA repair is independent of pyrimidine dimer excision and recombination plays a role in mutation fixation.

    Area of Science:

    • Microbiology
    • Molecular Biology
    • Genetics

    Background:

    • N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) is a potent mutagen used to induce premutational DNA damage.
    • Understanding DNA repair and mutation fixation mechanisms is crucial for comprehending mutagenesis.

    Purpose of the Study:

    • To investigate the repair and fixation of MNNG-induced premutational damage in Haemophilus influenzae.
    • To elucidate the roles of DNA elongation, pyrimidine dimer excision, and recombination in these processes.

    Main Methods:

    • Utilized a temperature-sensitive DNA elongation mutant (dna9) of Haemophilus influenzae, along with mutants deficient in pyrimidine dimer excision (uvr1, uvr2) and recombination (rec1).
    • Assessed DNA repair by monitoring mutation frequency decline with delayed DNA replication at restrictive temperatures.
    • Evaluated mutation fixation through transformation assays using DNA from MNNG-treated cells.

    Main Results:

    • DNA repair of MNNG-induced lesions occurred independently of the pyrimidine dimer excision system.
    • Mutation fixation was observed at both restrictive and non-restrictive temperatures, with less fixation at the restrictive temperature, suggesting lesions near and far from the replication fork contribute to mutations.
    • Newly synthesized DNA post-MNNG treatment showed reduced molecular weight, which normalized over time, a process inhibited in rec1 mutants, indicating recombination's involvement.

    Conclusions:

    • DNA repair in MNNG-treated Haemophilus influenzae is not dependent on pyrimidine dimer excision.
    • Recombination is implicated in the maturation of newly synthesized DNA following MNNG treatment, suggesting a role in MNNG mutagenesis.

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