Mga is a DNA-binding protein that activates the expression of several important virulence genes in Streptococcus pyogenes (group A Streptococcus, GAS) in response to changing environmental conditions. It had been found that the mouse transcription factor Max interacted with Mga.°Coimmunoprecipitation analysis confirmed that Max and Mga interacted in transfected HEK293 cells. EMSA revealed that Mga required Max for binding to the E-box sequence CACGTG. The isolated T-box of Mga bound the brachyury T-box-binding site in the absence of Max. Mga repressed transcription of a reporter driven from a T-box-binding site, but coexpression of Mga with Max caused transcriptional activation from the T-box-binding site. Expression of Mga with Max, but not Mga alone, activated transcription from a reporter containing the E-box site.