Characterization of the gntT gene encoding a high-affinity gluconate permease in Escherichia coli

We characterized the gntT gene encoding a high-affinity gluconate permease of Escherichia coli K-12. Primer extension and lacZ-operon fusion analyses revealed that gntT has one strong and two weak promoters, all of which are regulated positively by cAMP-CRP and negatively by GntR. The weak promoters became constitutive when separated from the upstream region including the strong promoter that overlaps a putative GntR-binding sequence. Gluconate-specific uptake activity was observed with cells harboring the gntT plasmid clone, which was enhanced by the presence of gntK encoding gluconate kinase.