FIG. 1.

Genetic organization of the 8-kb heme utilization gene cluster of B. pertussis. Arrows indicate the transcriptional orientations and spatial limits of the ECF regulator pair genes hurIR and the bhuRSTUV heme utilization operon. Circles represent the known Fur and iron-repressible promoter-operator region upstream of hurIR and the HurI-activated, heme-inducible promoter upstream of bhuRSTUV. Genes and products: hurI, transcriptional activator (ECF sigma factor); hurR, sensor/regulator protein; bhuR, outer membrane heme receptor protein; bhuS, heme chaperone protein; bhuT, periplasmic binding protein; bhuU, membrane permease; bhuV, ATP-binding protein. The deleted bhuR genetic region that was replaced by a kanamycin resistance cassette in B. pertussis mutant strain PM5 is indicated by the bar labeled ΔbhuR::kan.