Relationship of M protein genes in group A streptococci.

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Abstract
The M protein of group A streptococci is considered one of the primary virulence determinants of this organisms because it prevents phagocytosis. All of the 56 different M protein types of group A streptococci tested contain a DNA region that hybridizes with a labeled probe consisting of DNA encoding the type 6 M protein (emm6 gene). Two of 3 functionally M- group A strains (strains that are successfully phagocytized) also contain this gene, but this DNA is not present in 1 M- strain. Of the other streptococcal groups, only groups C and G, which are closely related to group A, contain DNA that hybridizes with emm6. None of the nonstreptococcal gram-positive bacteria tested contains emm6-related DNA. In the strain from which emm6 was cloned, there appears to be only a single copy of this gene.