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Hemimethylation prevents DNA replication in E. coli

D W Russell, N D Zinder

    Cell
    |September 25, 1987
    PubMed

    Insights

    DNA adenine methylase (dam) deficiency in E. coli hinders plasmid transformation. Unmethylated plasmids transform dam- bacteria efficiently, while hemimethylated ones do not, indicating dam methylation is crucial for replication initiation.

    Area of Science:

    • Molecular Biology
    • Genetics
    • Microbiology

    Background:

    • DNA adenine methylase (dam) in E. coli methylates adenines at GATC sequences.
    • Methylation status is critical for DNA replication and gene expression regulation.
    • E. coli strains deficient in dam methylase exhibit impaired plasmid transformation.

    Purpose of the Study:

    • To investigate the role of dam methylation in plasmid transformation efficiency.
    • To determine the impact of hemimethylated and unmethylated plasmids on dam- E. coli transformation.
    • To elucidate the mechanism by which dam methylation influences DNA replication initiation.

    Main Methods:

    • Transformation assays using methylated, hemimethylated, and unmethylated plasmids in dam- E. coli.
    • Analysis of plasmid replication and segregation in dam- strains.
    • Characterization of plasmid methylation status after transformation.

    Main Results:

    • Hemimethylated plasmids transform dam- E. coli poorly, while unmethylated plasmids transform them at high frequencies.
    • Fully methylated plasmids lead to accumulation of hemimethylated daughter molecules in dam- strains.
    • Plasmids purified from dam+ bacteria are often hemimethylated at specific sites.

    Conclusions:

    • DNA adenine methylase activity is essential for efficient plasmid transformation in E. coli.
    • Hemimethylation acts as a barrier to DNA replication initiation in dam- strains.
    • The methylation status of DNA, particularly hemimethylation, regulates the reinitiation of DNA replication in wild-type E. coli.

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