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DNA restriction-modification systems mediate plasmid maintenance

S Kulakauskas1, A Lubys, S D Ehrlich

  • 1Institut National de la Recherche Agronomique, Jouy-en-Josas, France.

Journal of Bacteriology
|June 1, 1995
PubMed

Insights

Restriction-modification systems enhance plasmid stability by killing plasmid-free cells. This involves methylase dilution, leading to DNA cleavage and cell death, a novel role for these systems.

Area of Science:

  • Molecular Biology
  • Microbiology
  • Genetics

Background:

  • Plasmid stability is crucial for maintaining genetic elements in bacterial populations.
  • Restriction-modification (R-M) systems are known for their roles in DNA defense and horizontal gene transfer.
  • The specific contribution of R-M systems to plasmid stability was previously uncharacterized.

Purpose of the Study:

  • To investigate the role of plasmid-carried restriction-modification systems in ensuring plasmid stability.
  • To elucidate the mechanism by which R-M systems confer segregational stability to plasmids.
  • To identify a previously unrecognized biological function of R-M systems.

Main Methods:

  • Studied EcoRI R-M system in Escherichia coli and Bsp6I R-M system in Bacillus subtilis.
  • Inactivated the endonuclease component or provided the methylase in trans.
  • Assessed plasmid stability and cell viability in the presence and absence of functional R-M systems.

Main Results:

  • Plasmid-carried R-M systems, EcoRI and Bsp6I, significantly enhance plasmid stability in their respective hosts.
  • Inactivation of the restriction endonuclease or providing the methylase in trans abolished the stabilizing effect.
  • Evidence suggests a post-segregational killing mechanism where loss of the methylase leads to host DNA cleavage.

Conclusions:

  • Restriction-modification systems play a significant role in maintaining plasmid stability through a post-segregational killing mechanism.
  • This mechanism involves the programmed death of plasmid-free cells upon dilution of the plasmid-encoded methylase.
  • The contribution to plasmid stability represents a novel biological role for R-M systems.

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