Characterization of TreR, the major regulator of the Escherichia coli trehalose system.

The pathway of trehalose utilization in Escherichia coli is different at low and high osmolarity. The low osmolarity system takes up trehalose as trehalose 6-phosphate which is hydrolyzed to glucose and glucose 6-phosphate. treB and treC, the genes for the enzymes involved, form an operon that is controlled by TreR (encoded by treR), the repressor of the system, for which trehalose 6-phosphate is the inducer. We have cloned and sequenced treR. The protein contains 315 amino acids with a molecular weight of 34,508. TreR was purified and shown to bind as a dimer trehalose 6-phosphate and trehalose with a Kd of 10 and 280 microM, respectively. The conformations of the protein differ from each other with either one or the other substrate-bound. Protease treatment removed the DNA-binding domain from the intact protein leaving the dimerization domain (a 29-kDa carboxyl-terminal fragment) intact. Nuclease protection experiments revealed a palindromic sequence located directly upstream of the -35 promoter sequence of treB that functions as the operator of the system.