Analysis of the effect exerted by extracellular pH on the maltose regulon in Escherichia coli K-12

The Escherichia coli maltose regulon consists of five operons under the control of the MalT transcriptional activator, lac operon fusions were constructed in vitro with the MalT-dependent promoter and with the malT promoter itself. beta-Galactosidase activity displayed by these fusions during growth at different external ph (pH(o)) revealed that growth at a ph, higher than 6 stimulates the transcription of malT- and MalT-controlled genes in the absence or presence of maltose. Using a malTp1 malTp10 promoter that is cAMP-CRP (cAMP receptor protein)-independent, it was demonstrated that CRP is essential for malT ph(o) regulation and that the pH(o)-dependent activity of malKp is a direct consequence of malT regulation. The ph, regulation displayed by a deleted but still functional malT promoter fused to lacZ demonstrates that this minimal promoter contains all the regulatory regions for establishing ph(o) regulation. In the absence of Mlc, a repressor of malT expression, the ph(o) regulation of malT was still effective. It is proposed that binding of cAMP-CRP at malTp may be affected by malTp topology induced by pH(o) or that a pH(o)-dependent effector may act in concert with the cAMP-CRP complex.