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Nucleotides critical for the interaction of the Streptococcus pyogenes Mga virulence regulator with Mga-regulated

Lara L Hause1, Kevin S McIver

  • 1Department of Cell Biology & Molecular Genetics and Maryland Pathogen Research Institute, University of Maryland, College Park, Maryland, USA.

Journal of Bacteriology
|July 10, 2012
PubMed

Insights

The Mga regulator of Streptococcus pyogenes binds DNA to control virulence factors. Researchers identified critical nucleotides within the Mga binding site, revealing a promoter-specific binding mechanism.

Area of Science:

  • Microbiology
  • Molecular Biology
  • Genetics

Background:

  • The Mga regulator controls virulence factor expression in Streptococcus pyogenes.
  • Mga binds to specific DNA sites to activate transcription of virulence genes like emm, scpA, and sic.
  • Existing Mga binding sites show low sequence identity, complicating understanding of Mga-DNA interactions.

Purpose of the Study:

  • To identify critical nucleotides within the Mga binding site essential for Mga-DNA interaction and transcriptional activation.
  • To elucidate the precise mechanism of Mga binding to promoter DNA.
  • To define a minimal Mga binding site.

Main Methods:

  • Electrophoretic mobility shift assay (EMSA) and DNase I protection assays to study Mga binding.
  • Site-directed mutagenesis of the Pemm1 binding site.
  • In vitro DNA binding assays and in vivo transcriptional activation assays using a luciferase reporter.
  • Methylation interference analysis of promoter DNA.

Main Results:

  • 34 nucleotides in the Pemm1 binding site were identified as critical for Mga binding and/or transcriptional activation.
  • Critical nucleotides, primarily guanine and cytosine, are clustered at the 5' and 3' ends, with intervening adenine runs.
  • A 35-bp minimal binding site (Pemm1) was defined, showing comparable Mga binding to the larger 45-bp site.
  • Mga exhibits promoter-specific DNA binding, as demonstrated by mutagenesis and methylation interference studies.

Conclusions:

  • The Mga binding site is characterized by specific nucleotide requirements and a defined structure.
  • Mga's interaction with DNA is promoter-specific, influencing the regulation of virulence genes.
  • Understanding Mga-DNA interactions provides insights into the transcriptional control of Streptococcus pyogenes virulence.

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