Regulation of enterobacterin ion transport in Escherichia coli: Characterization of ent::Mu d(Ap(r) lac) operon fusions

Abstract

The vector Mu d(Ap(r) lac) was utilized to construct operon fusions in the Escherichia coli enterobactin (ent) biosynthetic and transport genes. Enzyme assays indicated a 5- to 15-fold increase in the expression of β-galactosidase when the fusion strains were grown under iron-deficient conditions. The polarity effects seen by Mu d insertions into entA, entC, and entE were consistent with a single operon, entA(CGB)E. The direction of transcription from iron-regulated promoters was determined by directional transfer of selected genetic markers after the insertion of F'ts114 lac+. Regulatory mutants were isolated in the fusion strains by the selection for constitutive expression of β-galactosidase and the iron-regulated outer membrane proteins.