Group A streptococcal pyrogenic exotoxins (SPEs A, B, and C) are superantigens. SPE A shares high sequence similarity with Staphylococcus aureus enterotoxins (SEs) B and C. Since SPE A is bacteriophage-encoded, we hypothesized that its gene ( speA ) was acquired from S. aureus . speA , when cloned into S. aureus , was stably expressed, its protein resistant to proteases, and the gene under accessory gene regulator control. speA was acquired by streptococci from cross-species transduction. speB was not expressed in S. aureus. SPE C was degraded by staphylococcal proteases. The genes speB and speC were not recently acquired from S. aureus.
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