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Regulation of Escherichia Coli Adenylate Cyclase Activity during Hexose Phosphate Transport

Valérie Dumay

Martine Crasnier^,*,*

Unité de Régulation de l'Expression Génétique (Centre National de la Recherche Scientifique Unité Associée 1129), Institut Pasteur, 28 rue du Docteur Roux, 75724 Paris cedex 15, France

^* Author for correspondence: Martine Crasnier. Tel: +1 619 534 2608. Fax: +1 619 534 7108. e-mail: mcrasnier@ucsd.edu

ABSTRACT

In Escherichia coli cAMP levels vary with the carbon source used in the culture medium. These levels are dependent on the cellular concentration of phosphorylated EnzymeIIA^glc, a component of the glucose-phosphotransferase system, which activates adenylate cyclase (AC). When cells are grown on glucose 6-phosphate (Glc6P), the cAMP level is particularly low. In this study, we investigated the mechanism leading to the low cAMP level when Glc6P is used as the carbon source, i.e. the mechanism preventing the activation of AC by phosphorylated EnzymellA^glc. Glc6P is transported via the Uhp system which is inducible by extracellular Glc6P. The Uhp system comprises a permease UhpT and three proteins UhpA, UhpB and UhpC which are necessary for uhpT gene transcription. Controlled expression of UhpT in the absence of the regulatory proteins (UhpA, UhpB and UhpC) allowed us to demonstrate that (i) the Uhp regulatory proteins do not prevent the activation of AC by direct interaction with EnzymellA^glc and (ii) an increase in the amount of UhpT synthesized (corresponding to an increase in the amount of Glc6P transported) correlates with a decrease in the cAMP level. We present data indicating that Glc6P per se or its degradation is unlikely to be responsible for the low cAMP level. It is concluded that the level of cAMP in the cell is determined by the flux of Glc6P through UhpT.

Present address: University of California San Diego, Department of Biology, La Jolla, CA 92093-0116, USA.

Present address: RITE, 9-2 Kizugawadai, Kizu-cho, Soraku-gun, Kyoto 619-02, Japan.

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