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Related Experiment Videos

An SOS-inducible defective retronphage (phi R86) in Escherichia coli strain B.

J Kirchner1, D Lim, E M Witkin

  • 1Waksman Institute, Rutgers, State University of New Jersey, Piscataway 08553.

Molecular Microbiology
|October 1, 1992
PubMed
Summary

Constitutive SOS response in Escherichia coli via recA730 is lethal at high temperatures due to retronphage phi R86 induction. This phage inhibits DNA replication, causing cell death in specific bacterial strains.

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Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • The RecA protein in Escherichia coli controls the SOS response, a DNA damage-inducible survival mechanism.
  • The recA730 mutation leads to continuous SOS expression, which is lethal in certain bacterial strains (B/r) at high temperatures.

Purpose of the Study:

  • To investigate the cause of lethality associated with the recA730 mutation in Escherichia coli B/r strains.
  • To identify the role of retronphage phi R86 in the observed temperature-sensitive lethality.

Main Methods:

  • Comparative analysis of bacterial strains (B/r, K-12, and hybrids) with the recA730 mutation.
  • Investigating the induction of retronphage phi R86 and its genetic components (retron EC-86, msDNA-RNA, ORF336).
  • Assessing the impact of phi R86 induction on host DNA replication and cell viability.

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Main Results:

  • Lethality in recA730 B/r strains is caused by the SOS induction of an integrated defective retronphage, phi R86.
  • phi R86, absent in K-12 strains, contains genes for reverse transcriptase and msDNA-RNA.
  • Induction of phi R86 inhibits host DNA replication, preceding cell death. Overexpression of the phi R86 'killer' gene (ORF336) mimicked these effects.
  • phi R86 is not induced by UV in recA+ strains.

Conclusions:

  • The defective retronphage phi R86, integrated into the B/r chromosome, is responsible for the temperature-sensitive lethality observed with the recA730 mutation.
  • SOS induction of phi R86 disrupts host DNA replication, leading to cell death.
  • The retronphage killer gene ORF336 plays a critical role in the observed phenotype.