Membrane vesicles were characterized for their ability to specifically bind ["4C]glucose 6-phosphate. Membranes prepared from a strain carrying a ColEl uhp hybrid plasmid showed significantly enhanced glucose 6-phosphate binding. It is hypothesized that glucose 6-phosphate binding to these membranes is due to a uhpR-directed, membrane-bound receptor which functions in regulation of the inducible uhpT gene product: the hexose phosphate permnease.Escherichia coli can actively transport exogenous hexose phosphates into the cell via an inducible permease (2). This permease is the product of the uhpT gene, and its synthesis is induced only by the presence of external glucose 6-phosphate (G6P) (12). Intracellular G6P or other hexose phosphates, such as fructose 6phosphate (F6P), found externally do not induce permease production (3). This regulatory phenomenon is termed exogenous induction, and others (13) have hypothesized the involvement of a membrane receptor which would specifically bind to exogenous G6P and then somehow allow uhpT gene activation. Kadner (7) has identified a regulatory element (uhpR) of the uhp genes. We present evidence that the uhpR gene product is a membrane-bound receptor, specific for external G6P.E. coli strain CSR603 (F-Strr Gal-Uhp+ Rec-) was provided by A. Sancar and has been described elsewhere (11). E. coli JA200 (F+ Str8 Gal' Uhp+) was provided by J. Carbon and described elsewhere (1). Four JA200 strains were provided, each carrying a hybrid ColEl plasmid known to contain the uhp genes (R. Essenberg, personal communication). These four JA200 strains are designated 17-47, 35-4, 40-33, and 14-9. Conjugation between each of the four JA200 donors and the CSR603 recipient was carried out (10), and conjugates receiving the CoIEl uhp plasmid were selected by screening on nutrient agar-yeast extract plates containing streptomycin (200 Atg/ml) and colicin El (10%, vol/vol).ColEl colicin was prepared from chloroformtreated cultures of E. coli strain DB 1187. This strain has been shown to be a highly efficient producer of colicin El and was provided by D. Berg, Washington University, St. Louis, Mo., whose procedure for colicin preparation was t Present address: Department of Biological Sciences, University of Texas, Austin, TX 78703. used. Selected conjugates were also tested to demonstrate their Gal-phenotype. The largest number of conjugates was found resulting from the cross with JA200-17-47, and one of these colonies was chosen for further study. This conjugate, containing the ColEl uhp plasmid, was designated CSR603-17-47.The conjugate strain was tested in our laboratory for the presence of multiple copies of the uhp genes. It was found (data not shown) that the induced rate of G6P uptake (initial velocity) was 5.5 times greater in the conjugate than in the same strain which did not contain the ColEl hybrid plasmid. Both strains displayed similar degrees of uhp inducibility, indicating the presence of normal regulation of the hexose phosphate transport process. These findings indicate that ...