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Theuhp locus ofEscherichia coli contains genes for the sugar phosphate transport system (uhpT ) and the regulatory system which allows its induction by external glucose 6-phosphate (uhpRA ). Theuhp region was cloned onto high-copy-number plasmids, both from Uhp+ plasmids of the Clarke-Carbon collection and from genetically characterized specialized transducing phages carryinguhpT-lac operon fusions. Two Clarke-Carbon plasmids and their Uhp+ subclones in pBR322 shared restriction sites defining theuhp region, but exhibited different regulation of Uhp expression and dependence on chromosomaluhp genotype. Plasmid pLC17-47 and derivatives conferred constitutive glucose 6-phosphate uptake activity in all strains, even those with complete deletions ofuhp . These plasmids also rendered constitutive the expression of a chromosomaluhpT-lac operon fusion. Plasmid pLC40-33 conferred inducible Uhp expression, which required the presence of theuhpA + gene on the chromosome. The induced transport levels in all strains carrying these plasmids were not appreciably amplified over haploid levels. Similar behavior was seen with the cloned operon fusions. A fusion-bearing plasmid that carried an intact regulatory system (uhpR + A + ) exhibitedtrans -dominant constitutive expression of β-galactosidase, regardless of the chromosomaluhp genotype. In contrast, the cloned fusion carrying onlyuhpR + gave glucose 6-phosphate-inducible production of β-galactosidase that was dependent on the presence of chromosomaluhpA + . Expression of both fusions in the haploid state was inducible. From these results, it was concluded that theuhpA product is necessary foruhpT transcription and that elevated dosage ofuhpA results in at least partially constitutive expression ofuhpT . A tentative model foruhp regulation is presented.

journal of bacteriology

Molecular Cloning of the <i>uhp</i> Region and Evidence for a Positive Activator for Expression of the Hexose Phosphate Transport System of <i>Escherichia coli</i>

Molecular Cloning of the uhp Region and Evidence for a Positive Activator for Expression of the Hexose Phosphate Transport System of Escherichia coli