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Structural and functional characterization of MrpR, the master repressor of the Bacillus subtilis prophage SPβ

Katharina Kohm1,2, Ekaterina Jalomo-Khayrova3, Aileen Krüger4

  • 1FG Synthetic Microbiology, Institute for Biotechnology, BTU Cottbus-Senftenberg, Senftenberg, Germany.

Nucleic Acids Research
|August 21, 2023
PubMed

Insights

The SPβ prophage

Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • Bacteriophages, specifically prophages, exhibit dynamic lifestyles, switching between lysogeny and lytic cycles.
  • The Bacillus subtilis SPβ prophage's lysogenic state is regulated by the MrpR (YopR) protein, a critical element in the lysis-lysogeny decision.
  • Understanding this regulation is key to controlling phage behavior and host-phage interactions.

Purpose of the Study:

  • To investigate the role of the MrpR protein in the SPβ prophage's lysis-lysogeny decision.
  • To characterize the structural and functional impact of a temperature-sensitive mutation in the mrpR gene.
  • To identify novel components involved in the SPβ prophage's lytic cycle induction.

Main Methods:

  • Utilizing a heat-sensitive SPβ c2 mutant strain of Bacillus subtilis.
  • Employing structural characterization of the MrpR protein.
  • Performing genome-wide profiling of MrpR DNA-binding activity.
  • Conducting suppressor mutant analysis to identify new regulatory factors.

Main Results:

  • A single nucleotide exchange in the mrpR gene confers temperature sensitivity to the MrpRG136E protein, inducing the SPβ c2 lytic cycle upon heat treatment.
  • Structural analysis reveals MrpR as a DNA-binding protein, distinct from functional tyrosine recombinases, with impaired DNA binding due to the G136E mutation.
  • MrpR acts as a master repressor, binding to the SPbeta repeated element (SPBRE) to maintain lysogeny.
  • The heat-inducible excision of SPβ c2 depends on the serine recombinase SprA.
  • A novel component essential for SPβ lytic cycle induction was identified through suppressor mutant analysis.

Conclusions:

  • The MrpR protein is a master repressor of SPβ lysogeny, binding to SPBRE to maintain the integrated state.
  • The temperature-sensitive MrpRG136E mutation disrupts MrpR's structure and DNA-binding, enabling heat-induced prophage activation.
  • The study reveals a new factor crucial for SPβ prophage induction, expanding our understanding of phage regulatory networks.

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