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SOS mutator activity: unequal mutagenesis on leading and lagging strands

M Maliszewska-Tkaczyk1, P Jonczyk, M Bialoskorska

  • 1Institute of Biochemistry and Biophysics, Polish Academy of Sciences, Pawinskiego 5A, 02-106 Warsaw, Poland.

Proceedings of the National Academy of Sciences of the United States of America
|October 26, 2000
PubMed

Insights

The inducible SOS response in E. coli causes mutagenesis. Constitutive SOS activation (SOS mutator) in recA730 strains leads to reduced replication fidelity, with the lagging strand being most susceptible to these errors.

Area of Science:

  • Molecular Biology
  • Genetics
  • Microbiology

Background:

  • Mutagenesis in Escherichia coli is significantly influenced by the inducible SOS response.
  • Current models propose RecA and UmuD'(2)C protein interactions with stalled replication complexes mediate error-prone DNA synthesis.
  • The exact mechanisms of SOS-mediated DNA lesion bypass and mismatch extension remain unclear.

Purpose of the Study:

  • To investigate differential effects on replication fidelity between leading and lagging strands during constitutive SOS activation (SOS mutator) in E. coli.
  • To elucidate the strand-specific mechanisms underlying SOS mutator activity.

Main Methods:

  • Utilized recA730 E. coli strains exhibiting constitutive SOS response and a spontaneous mutator effect.
  • Constructed strain pairs with differing lac operon orientations relative to the replication origin to assess leading vs. lagging strand replication.
  • Employed mismatch-repair defective (mutL) strains to efficiently detect replication errors in the lacZ gene.

Main Results:

  • Observed significant differences in lac mutant frequencies between the two orientations, indicating strand-specific mutagenesis.
  • Found that the direction of the mutation frequency bias was reversed compared to normal E. coli cells.
  • Identified the lagging strand as being particularly vulnerable to the SOS mutator effect.

Conclusions:

  • SOS mutator activity exhibits significantly different efficiencies on the leading and lagging strands of DNA replication.
  • The lagging strand is disproportionately affected by the SOS mutator effect, leading to increased mutagenesis.
  • These findings provide critical insights into the strand-biased mechanisms of DNA repair and mutagenesis in E. coli.

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