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

Laboratoire de Microbiologie et Génétique Moléculaire, Centre de Génétique Moléculaire et Cellulaire, UMR CNRS 5534, Université Claude Bernard, 69622 Villeurbanne Cedex, France

ABSTRACT

Summary: 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. β-Galactosidase activity displayed by these fusions during growth at different external pH (pH_o) revealed that growth at a pH_o 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_o 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.

Author for correspondence: Patrick Laloi. Tel: +33 472 431 621. Fax: + 33 472 431 971. e-mail: plaloi@biomserv.univ-lyonl.fr

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