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Identification of a gene that regulates expression of M protein, the major virulence determinant of group A
1Department of Microbiology and Immunology, Emory University Health Sciences Center, Atlanta, GA 30322.
Abstract:
By using Tn916 insertional mutagenesis, we have identified mry (M protein RNA yield), a gene required for high-level expression of the M protein, an essential virulence determinant of the group A streptococcus. The mry::Tn916 mutation causes a reduction by a factor of approximately equal to 50 in the amount of M protein produced, in the original strain and in a nonmutagenized host to which the mutation was transferred by transduction. The insertion is located approximately 1.8 kilobases upstream of the structural gene for M protein (emm) and its promoter. The genomic region including mry::Tn916 and emm was cloned on a cosmid vector and introduced into Escherichia coli. When the transposon excised precisely from the chimeric cosmid in E. coli, the resulting streptococcal DNA showed the same restriction pattern as the homologous chromosomal region in the parental nonmutagenized streptococcus. The sequence of the promoter for emm was not altered in the mry mutant. The reduction in protein correlates with a decrease in the amount of M protein-specific mRNA, indicating that mry regulates transcription of emm.
Insights
Researchers identified the mry gene, crucial for high-level M protein production in group A Streptococcus. This discovery impacts understanding of bacterial virulence and gene regulation.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Group A Streptococcus (GAS) is a significant human pathogen.
- M protein is a key virulence factor in GAS, mediating host immune evasion.
- Understanding the regulation of M protein expression is critical for developing targeted therapies.
Purpose of the Study:
- To identify genetic factors regulating the expression of M protein in Group A Streptococcus.
- To characterize a novel gene, mry, involved in M protein RNA yield.
Main Methods:
- Tn916 insertional mutagenesis was employed to identify genes affecting M protein expression.
- Transduction was used to transfer the mry::Tn916 mutation into different streptococcal strains.
- Cosmid cloning and subsequent precise transposon excision in Escherichia coli were performed to analyze the genomic region.
- Quantitative analysis of M protein and M protein-specific mRNA levels was conducted.
Main Results:
- A Tn916 insertion mutation in the mry gene led to a ~50-fold decrease in M protein production.
- The mry gene is located upstream of the emm gene (M protein structural gene) and its promoter.
- The mutation reduced M protein-specific mRNA levels, indicating transcriptional regulation.
- The emm promoter sequence remained unaltered in the mry mutant.
Conclusions:
- The mry gene is essential for high-level M protein expression in Group A Streptococcus.
- mry likely regulates the transcription of the emm gene, controlling M protein production.
- This finding provides new insights into the molecular mechanisms of GAS virulence factor regulation.