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Mutation induction by MNNG in a bacteriophage of Haemophilus influenzae

M E Boling, R F Kimball

    Mutation Research
    |October 1, 1976
    PubMed

    Insights

    N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) treatment induced reversion in Haemophilus influenzae phage HP1c1 mutants. Phage DNA replication, not host-cell DNA synthesis, is crucial for fixing mutations in phage DNA.

    Area of Science:

    • Microbiology
    • Molecular Biology
    • Genetics

    Background:

    • Haemophilus influenzae phage HP1c1 is a model organism for studying viral genetics.
    • Temperature-sensitive mutants are valuable tools for investigating DNA replication and mutation fixation processes.
    • Understanding mutagenic mechanisms is crucial for viral evolution and control.

    Purpose of the Study:

    • To investigate the reversion frequencies of temperature-sensitive mutants of Haemophilus influenzae phage HP1c1.
    • To determine the role of phage and host DNA synthesis in the fixation of mutations induced by N-methyl-N itro-N-nitrosoguanidine (MNNG).

    Main Methods:

    • Treatment of lysogenic cells and infected cells with MNNG.
    • Analysis of reversion frequencies of phage mutants (ts1, ts2, ts3) to wild type (ts+).
    • Assessment of host-cell and phage DNA synthesis during mutation fixation.

    Main Results:

    • MNNG treatment induced reversion in phage HP1c1 mutants at frequencies up to 0.1%.
    • Reversion frequencies were similar when MNNG-treated cells were infected with whole ts phage, but not when MNNG-treated cells or phage were treated alone.
    • Mutation fixation occurred without host-cell DNA synthesis, implicating phage DNA synthesis in the process.
    • Prophage DNA replication within the host genome resulted in similar reversion rates as phage DNA replication outside the host.
    • Mutant ts3 showed a significantly lower induced reversion frequency compared to ts1 and ts2.

    Conclusions:

    • Phage DNA replication is essential for the fixation of MNNG-induced premutational lesions in Haemophilus influenzae phage HP1c1.
    • The cellular replication machinery can support the fixation of mutations in phage DNA, whether integrated as prophage or replicating independently.
    • Differential reversion frequencies among mutants suggest specific mutational sites or mechanisms influencing MNNG sensitivity.

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