COMPLEMENTATION OF DIVERGENT MGA GENES IN GROUP-A STREPTOCOCCUS

The gene (mga4) encoding the positive regulatory protein, Mga4, was cl oned and sequenced from an M type 4 strain (AP4) of Streptococcus pyog enes. The deduced amino acid (aa) sequence of this 'divergent Mga' sho ws 88% identity to the prototype Mga1 in its N-terminal half, which co ntains all three of the predicted helix-turn-helix domains. However, o ne of the predicted receiver domains of Mga1, which is at its C termin us, is not conserved in the Mga4 aa sequence. Nevertheless, a mutation in mga1 was found to be complemented for activation of the gene encod ing M protein (emm) by mga4 in trans. This suggests that the aa residu es of the C-terminal predicted receiver domain are not critical for ac tivation of emm transcription.