ANALYSIS OF THE ERWINIA-CHRYSANTHEMI FERRICHRYSOBACTIN RECEPTOR GENE - RESEMBLANCE TO THE ESCHERICHIA-COLI FEPA-FES BIDIRECTIONAL PROMOTER REGION AND HOMOLOGY WITH HYDROXAMATE RECEPTORS

The fct cbsCEBA operon from the Erwinia chrysanthemi 3937 chrysobactin -dependent iron assimilation system codes for transport and biosynthet ic functions. The sequence of the fct outer membrane receptor gene was determined. The fct promoter region displays a strong resemblance to the Escherichia coli bidirectional intercistronic region controlling t he expression of the fepA-entD and fes-entF operons. An apparent Fur-b inding site was shown to confer iron regulation on an fct::lac fusion expressed on a low-copy-number plasmid in a Fur-proficient E. coli str ain. The fct gene consists of an open reading frame encoding a 735-ami no-acid polypeptide with a signal sequence of 38 residues. The Fct pro tein has 36% sequence homology with the E. coli ferrichrome receptor F huA and the Yersinia enterocolitica ferrioxamine receptor FoxA. On the basis of secondary-structure predictions and these homologies, we pro pose a two-dimensional folding model for Fct.