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Complementation of divergent mga genes in group A Streptococcus
G Andersson1, K McIver, L O Hedén
1Department of Microbiology, Lund University, Sweden.
Abstract:
The gene (mga4) encoding the positive regulatory protein, Mga4, was cloned and sequenced from an M type 4 strain (AP4) of Streptococcus pyogenes. The deduced amino acid (aa) sequence of this "divergent Mga' shows 88% identity to the prototype Mga1 in its N-terminal half, which contains all three of the predicted helix-turn-helix domains. However, one of the predicted receiver domains of Mga1, which is at its C terminus, is not conserved in the Mga4 aa sequence. Nevertheless, a mutation in mga1 was found to be complemented for activation of the gene encoding M protein (emm) by mga4 in trans. This suggests that the aa residues of the C-terminal predicted receiver domain are not critical for activation of emm transcription.
Insights
The Streptococcus pyogenes mga4 gene encodes a Mga4 protein that activates emm gene transcription. Mga4 shares high similarity with Mga1, but lacks a C-terminal receiver domain, yet still activates emm transcription, indicating this domain is not critical.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Streptococcus pyogenes utilizes Mga (M protein gene regulator) to control virulence gene expression.
- Mga1 is a known positive regulator of the emm gene, crucial for M protein production.
- Understanding Mga protein function is key to deciphering S. pyogenes pathogenesis.
Purpose of the Study:
- To clone and characterize the mga4 gene from Streptococcus pyogenes M type 4 strain AP4.
- To investigate the functional role of the Mga4 protein in regulating emm gene transcription.
- To compare the structural and functional characteristics of Mga4 with the prototype Mga1.
Main Methods:
- Gene cloning and sequencing of mga4 from S. pyogenes AP4.
- Deduced amino acid sequence analysis and comparison with Mga1.
- Complementation assays to assess Mga4's ability to activate emm transcription in trans.
Main Results:
- The mga4 gene was successfully cloned and sequenced.
- The deduced Mga4 protein sequence showed 88% identity to Mga1 in the N-terminal half, containing helix-turn-helix domains.
- A C-terminal receiver domain present in Mga1 was not conserved in Mga4.
- Mga4 complemented a mutation in mga1, activating emm gene transcription.
Conclusions:
- The mga4 gene encodes a functional positive regulatory protein, Mga4.
- The C-terminal receiver domain of Mga1 is not essential for activating emm gene transcription.
- Mga4 represents a divergent Mga protein with conserved regulatory function.