SPECIFIC BINDING OF THE ACTIVATOR MGA TO PROMOTER SEQUENCES OF THE EMM AND SCPA GENES IN THE GROUP-A STREPTOCOCCUS

Transcription of the surface-associated virulence factors of the group A streptococcus (GAS) Streptococcus pyogenes, M protein (emm) and the C5a peptidase (scpA), is activated by a protein called Mga formerly M ry or VirR). To determine whether Mga binds directly to the promoters of the genes it regulates, a protein resulting from the fusion of Mga to the C-terminal end of maltose-binding protein was purified from Esc harichia coli. Specific binding to the promoter regions of the scpA an d emm alleles of the type M6 GAS strain JRS4 was demonstrated by elect rophoresis of the DNA-protein complex. Competition studies showed that the region upstream of scpA bound MBP-Mga with a slightly higher affi nity than did the region upstream of emm. DNase I protection experimen ts identified a single 45-bp binding site immediately upstream of and overlapping the -35 region of both promoters. Sequences homologous to the protected regions were found in the promoters of many emm, sep, an d emm like genes from strains of different serotypes of GAS, and a con sensus Mga binding site was deduced.