Expression of the pho regulon interferes with induction of the uhpT gene in Escherichia coli K-12

The uptake of hexose 6-phosphates in Escherichia coli is mediated by the tr ansporter UhpT, the synthesis of which is induced by the presence of glucos e 6-phosphate (glucose 6-P) in the medium. Since this protein functions as an anion exchanger, it is generally assumed to be geared for the use of sug ar phosphates as a carbon source. However, the question was unresolved whet her this transporter can also provide the cells with glucose 6-P as a phosp hate source. It is demonstrated in this work that UhpT-mediated glucose 6-P uptake does not allow the cells to grow on glucose 6-P as phosphate, sourc e. Hence, the expression of UhpT under phosphate limitation would not be pa rticularly advantageous and some form of interaction between the uhp system and the Pi-limitation-inducible pho regulon, the products of which are inv olved in phosphate acquisition, may be anticipated. Indeed, the use of an u hpT-lacZ fusion revealed that much higher concentrations of the inducer glu cose 6-P were required to elevate uhpT transcription when the pho regulon w as expressed. This interference was the result of degradation of glucose 6- P by one of the products of the pho regulon, the periplasmic enzyme alkalin e phosphatase. The specific form of interaction between the Pho and Uhp sys tems is designated inducer degradation.