Cloning and expression of the fhu genes involved in iron(III)-hydroxamate uptake by Escherichia coli

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Abstract
The fhu region, located at the 3.5 min region of the linkage map, codes for transport functions for the 4 hydroxamate compounds, ferrichrome, aerobactin, rhodotorulic acid and coprogen, which transport Fe3+ into E. coli. The fhu region was cloned into pBR322. By restriction analysis, Tn5 insertion mutations and complementation studies between plasmid fragments and chromosomal mutants at least 4 loci in the order fhuA, fhuC, fhuD, fhuB were found. The genetic products were determined in maxicells and minicells. fhuA codes for the known 78,000 dalton receptor protein and the 81,000 dalton precursor in the outer membrane; fhuC codes for a 30,000-dalton protein; fhuD encodes a 26,000 dalton protein in the cytoplasmic membrane. No protein(s) could be assigned to the fhuB region. Truncated proteins derived from partial fhuA genes (68,000, 42,000 and 39,000 daltons) and a partial fhuD gene (24,000 daltons) and the strong polar effect on the expression of the genes indicated the direction of transcription to be from fhuA to fhuD.