INVOLVEMENT OF THE CENTRAL LOOP OF THE LACTOSE PERMEASE OF ESCHERICHIA-COLI IN ITS ALLOSTERIC REGULATION BY THE GLUCOSE-SPECIFIC ENZYME IIAOF THE PHOSPHOENOLPYRUVATE-DEPENDENT PHOSPHOTRANSFERASE SYSTEM

Allosteric regulation of several sugar transport systems such as those specific for lactose, maltose and melibiose in Escherichia coli (indu cer exclusion) is mediated by the glucose-specific enzyme IIA (IIA(Glc )) of the phosphoenolpyruvate:sugar phosphotransferase system (PTS). D eletion mutations in the cytoplasmic N and C termini of the lactose pe rmease protein, LacY, and replacement of all cysteine residues in LacY with other residues did not prevent IIA(Glc)-mediated inhibition of l actose uptake, but several point and insertional mutations in the cent ral cytoplasmic loop of this permease abolished transport regulation a nd IIA(Glc) binding. The results substantiate the conclusion that regu lation of the lactose permease in E. coli by the PTS is mediated by a primary interaction of IIA(Glc) with the central cytoplasmic loop of t he permease.