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Small DNA deletions creating avirulence in Streptococcus pyogenes
Abstract:
The M protein is the antigen on the surface of group A streptococci that allows these bacteria to resist phagocytosis. DNA encoding the M12 protein was cloned into Escherichia coli and used as an isotopically labeled hybridization probe to compare genomic DNA's isolated from M+ and M- isogenic cultures in an effort to elucidate the genetic basis of this variation. DNA's from two spontaneous, independent M- variants contained small (approximately 50 base pairs) deletions which were mapped to identical restriction fragments within or adjacent to the M protein coding sequence. Taken together with the pleiotropic nature of these deletions, this suggests that they define a regulatory switch.
Insights
Group A streptococci resist phagocytosis using M protein. Researchers found small DNA deletions in M- variants, suggesting a regulatory switch controls M protein expression and bacterial defense mechanisms.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Group A streptococci (GAS) possess surface M proteins crucial for evading host phagocytosis.
- Understanding the genetic regulation of M protein expression is key to controlling GAS infections.
Purpose of the Study:
- To investigate the genetic basis for variation in M protein expression in group A streptococci.
- To identify genetic elements responsible for the loss of M protein (M-) in isogenic cultures.
Main Methods:
- Cloning of DNA encoding the M12 protein into Escherichia coli.
- Utilizing isotopically labeled M12 DNA as a hybridization probe.
- Comparing genomic DNA from M+ (M protein positive) and M- (M protein negative) isogenic GAS cultures.
Main Results:
- Two independent spontaneous M- variants exhibited small deletions (approx. 50 base pairs).
- These deletions were mapped to identical restriction fragments.
- The deletions were located within or adjacent to the M protein coding sequence.
Conclusions:
- The identified deletions likely represent a regulatory switch controlling M protein expression.
- These findings provide insight into the genetic mechanisms underlying M protein variation in group A streptococci.
- The pleiotropic nature of the deletions suggests a broader regulatory role.