FIG. 3.

Genetic organization of the B. pertussis heme iron uptake system and comparison with the E. coli ferric citrate uptake system. (Top) B. pertussis DNA region containing the bhu genes and the upstream hurIR open reading frames. Vertical bars upstream of hurI and bhuR show the positions of Fur-binding sequences which were predicted by nucleotide sequence analysis and which were assessed in vivo with the Fur repressor titration assay. (Bottom) Organization of the fec genetic system of E. coli (11), with putative Fur-binding sites denoted by vertical bars upstream of fecI and fecA. fecI and fecR encode positive regulatory proteins; fecA codes for the outer membrane ferric citrate receptor; fecB, fecC, fecD, and fecE encode periplasmic binding protein and cytoplasmic membrane transport components.