Insertional inactivation of virR in Streptococcus pyogenes M49 demonstrates that VirR functions as a positive regulator of ScpA, FcRA, OF, and M protein.

Several reports have shown that Streptococcus pyogenes strains which produce opacity factor (OF+) have diverged significantly from OF- serotypes. This study questions whether several surface proteins of an OF+ culture are regulated by the positive regulatory protein VirR, in a manner similar to OF- strains. Interruption of the virR region of an OF+ S. pyogenes (strain CS101, M type 49) was performed using a temperature-sensitive plasmid containing a fragment of virR. Interruption of the virR region produced cultures with undetectable amounts of M49 and ScpA proteins, and reduced the yield of FcRA protein. In addition, mutants had a significant reduction in detectable opacity factor. These results suggest that virR functions as a positive regulator of a variety of surface proteins in OF+ strains.