Schematic view of the gene loci encoding fhaB in B. pertussis , B. avium and B. holmesii. Relevant genes are represented as boxes. The arrows below the boxes show the transcriptional polarity of each gene. The open reading frame orfMP of B. holmesii encoding a putative membrane is not yet completely sequenced. The shaded regions (marked A to D) within the fhaB gene of B. holmesii indicate the degree of similarity of the deduced protein sequence with that of the FHA protein of B. avium. Region A comprises approximately amino acids 1–850, region B amino acids 950 to 1,640, region C amino acids 1,900 to 2,600, and region D amino acids 2,830 to 2,930 of the B. holmesii FHA protein; these regions correspond to amino acids 1–820, 840–1,540, 1,600–2310, and 2,520–2621 of the B. avium protein, respectively.