[The vir-regulon of Streptococcus pyogenes: coordinate expression of important virulence factors]

Streptococcus pyogenes (group A streptococci; GAS) expresses important virulence factors like the antiphagocytic M protein, the complement factor-inactivating C5a peptidase and the immunoglobulin-Fc-binding proteins on its surface. The corresponding emm, scpA, and emm-related (fcrA, ennX) genes are adjacently encoded on the genome. They are coordinately in trans regulated by the positive regulatory VirR factor. The responsible virR gene is also located within this segment of the genome which was called vir-regulon. There are at least three different types of organization of the vir-regulon. A frequently encountered type is the "Large vir-regulon". It comprises from 5' to 3' the following genes: virR, fcrA, a relatively small emm, ennX, and a 4.6 kb version of scpA. Another common type is the "Small vir-regulon", which contains a virR deviating in its 3'-region, a relatively large emm, and a 3.5 kb version of scpA. The "Unusual vir-regulon" is less frequently detected. It closely resembles the small one, but harbors an additional 3 to 4 kb DNA fragment between emm and scpA, occasionally encoding an emm-related gene. The type of vir-regulon encoded by a GAS strain correlates to its serotype, its M class, and its expression of serum opacity factor. The structural genes of the vir-regulon are expressed at a high level during growth in exponential phase, under anaerobiosis, and at body temperature. The sensor molecule which modulates VirR activity according to these environmental conditions has not yet been detected.(ABSTRACT TRUNCATED AT 250 WORDS)