Regulatory interactions involving the proteins of the phosphotransferase system in enteric bacteria

Sugar uptake and cytoplasmic inducer generation as well as cyclic AMP synthesis are regulated by the phosphoenolpyruvate:sugar phosphotransferase system (PTS) in Gram-negative enteric bacteria. In these organisms, the free form of the glucose-specific Enzyme IIA (IIAglc) of the PTS, which can be phosphorylated on a histidyl residue by PEP and the PTS energy coupling proteins, inhibits the activities of non-PTS carbohydrate permeases and catabolic enzymes. By contrast, the phosphorylated form of IIAglc appears to activate adenylate cyclase, the cyclic AMP biosynthetic enzyme. What is known of the molecular details of these regulatory interactions will be summarized, and a novel regulatory mechanism involving the fructose repressor, FruR, which controls the transcription of genes encoding enzymes which catalyze reactions in central pathways of carbon metabolism, will be presented.