Regulates the expression of the mymA operon (Rv3083-Rv3089). Induced at acidic pH. Negatively autoregulated. Phosphorylated by PknK. Phosphorylation increases affinity for the mymA promoter. Mutant displays altered colony morphology and cell wall structure, reduced contents and altered composition of mycolic acids along with the accumulation of saturated C24 and C26 fatty acids, and enhanced susceptibility to antibiotics, detergents and acidic pH. Also impairs ability to survive in activated macrophages, but not in resting macrophages.