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Activation of the Salmonella typhimurium Mrr protein

Abram Aertsen1, Mehari Tesfazgi Mebrhatu, Chris W Michiels

  • 1Laboratory of Food Microbiology, Centre for Food and Microbial Technology, Department of Microbial and Molecular Systems (M(2)S), Faculty of Bioscience Engineering, K.U.Leuven, Kasteelpark Arenberg 22, B-3001 Leuven, Belgium.

Biochemical and Biophysical Research Communications
|January 8, 2008
PubMed

Insights

The Mrr protein in Salmonella Typhimurium does not activate under high pressure. However, mutations can cause constitutive activation, leading to DNA damage and the SOS response, suggesting a role in cellular defense.

Area of Science:

  • Molecular Biology
  • Microbiology
  • Bacterial Genetics

Background:

  • The Mrr protein is a type IV restriction endonuclease in Escherichia coli K12, recognizing methylated DNA.
  • High pressure stress can activate E. coli Mrr, causing DNA double-strand breaks and inducing the SOS response.

Purpose of the Study:

  • To investigate the Mrr activity in Salmonella Typhimurium LT2.
  • To identify mutations leading to constitutive Mrr activation and understand their physiological implications.

Main Methods:

  • Cloning the mrr gene into an expression vector.
  • Isolation and analysis of spontaneous Mrr mutants.
  • Characterization of mutations affecting Mrr activity and SOS induction.

Main Results:

  • No high-pressure induced activation of Mrr was observed in Salmonella Typhimurium LT2.
  • Numerous constitutively activated Mrr mutants were isolated upon cloning the mrr gene.
  • Single point mutations were identified that confer constitutive Mrr activity.
  • A chromosomal mrr mutation resulted in increased basal SOS induction in S. Typhimurium.

Conclusions:

  • Mrr activity in S. Typhimurium differs from E. coli regarding pressure activation.
  • Constitutive activation of Mrr through mutations can lead to DNA damage and SOS response.
  • The findings suggest a potential role for Mrr in cellular defense mechanisms, possibly related to DNA integrity.

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