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Related Experiment Videos

Small DNA deletions creating avirulence in Streptococcus pyogenes.

J G Spanier, S J Jones, P Cleary

    Science (New York, N.Y.)
    |August 31, 1984
    PubMed
    Summary

    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.

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    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.

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