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Transcriptional analysis of mga, a regulatory gene in Streptococcus pyogenes: identification of monocistronic and
1Department of Microbiology, University of Minnesota, Minneapolis 55455, USA.
Abstract:
Transcription of several surface virulence proteins of Streptococcus pyogenes is regulated by Mga, a protein that shows homology to response regulators of two-component signal-transducing systems. Two of these surface virulence proteins, M protein and C5a peptidase, undergo phase variation. To determine whether Mga itself undergoes phase variation and might allow the phasing switch to coordinate the activity of these genes, expression of the mga gene was analyzed. We show for the first time that there are two mga-specific transcripts: a 3.8-kb bicistronic message that includes both mga and emm12 genes and a monocistronic 1.6-kb mga message. Both transcripts phase vary and are present in higher amounts in M+ variants than in M- variants. Incubation of RNA with rifampicin indicates that the smaller 1.6-kb message is not a processed product. Two promoters were mapped upstream of mga: P1 at position 666 (-395) and P2 at position 978 (-83). In strain CS46 (delta mga), transcription initiation from the P1 promoter does not occur, and multiple start sites are found around the P2 promoter. Complementation experiments indicate that sequences upstream of the P2 promoter are required for activation of emm12 and scpA by Mga in trans.
Insights
The Mga regulator in Streptococcus pyogenes controls virulence gene expression and undergoes phase variation. This study reveals two Mga transcripts that phase vary, influencing virulence factor production.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Streptococcus pyogenes virulence is regulated by the Mga protein, homologous to response regulators.
- M protein and C5a peptidase, surface virulence factors, exhibit phase variation.
Purpose of the Study:
- To investigate if the Mga regulator itself undergoes phase variation.
- To determine if Mga phase variation coordinates virulence gene activity.
Main Methods:
- Analysis of mga gene expression and transcript levels.
- Mapping of promoter regions upstream of mga.
- Complementation experiments in a delta mga strain.
Main Results:
- Two distinct mga transcripts (3.8-kb bicistronic and 1.6-kb monocistronic) were identified.
- Both transcripts exhibit phase variation, with higher levels in M+ variants.
- Two promoters (P1 and P2) were mapped, with P2 being crucial for transcription in a delta mga strain.
Conclusions:
- Mga undergoes phase variation, suggesting a role in coordinating virulence gene expression.
- Specific promoter elements upstream of P2 are essential for Mga-mediated activation of emm12 and scpA.