Common accessory genes for the Bordetella pertussis filamentous hemagglutinin and fimbriae share sequence similarities with the papC and papD gene families.

The Bordetella pertussis filamentous hemagglutinin (FHA) is a major virulence factor responsible for attachment, one of the early events in bacterial pathogenesis. Deletion of its structural gene, fhaB, or a Tn5 insertion in fhaA, downstream of fhaB, resulted in a FHA‐ and fimbriae‐ phenotype, although fhaB and the fim genes are not linked. The fhaB downstream region therefore most likely encodes accessory proteins required for the biosynthesis of FHA and fimbriae, despite the lack of sequence similarities between these two proteins. The nucleotide sequence of this area contains the open reading frames fhaD and fhaA, whose products share sequence similarities with the papD and papC gene products, respectively. PapD is a periplasmic chaperone protein able to bind to the Escherichia coli P pilin subunits and to transport them towards the outer membrane protein PapC which is responsible for pilus membrane translocation. An additional open reading frame, fhaE, is located downstream of fhaA. Its amino acid sequence shares similarities with those of the fimbrial subunits. Deletion analyses suggest that fhaB and the downstream genes can be transcribed as a polycistronic operon, and primer extension analysis revealed the presence of a second promoter between fhaB and fhaD.