Nucleotide sequence analysis of hypervariable junctions of Haemophilus influenzae pilus gene clusters

Haemophilus influenzae pill are surface structures that promote attachment to human epithelial cells. The five genes that encode pill, hifABCDE, are f ound inserted in genomes either between pmbA and hpt (hif-1) or between pur E and pepN (hif-2), We determined the sequence between the ends of the pilu s clusters and bordering genes in a number of H, influenzae strains. The ju nctions of the hif-1 cluster (limited to biogroup aegyptius isolates) are s tructurally simple. In contrast, hif-2 junctions are highly diverse, comple x assemblies of conserved intergenic sequences (including genes hicA and hi cB) with evidence of frequent recombination, Variation at hif-2 junctions s eems to be tied to multiple copies of a 23-bp Haemophilus intergenic dyad s equence. The hif-1 cluster appears to have originated in biogroup aegyptius strains from invasion of the hpt-pmbA region by a DNA template containing the hif-2 genes with termini in the hairpin loop of flanking intergenic dya d sequences, The pilus gene clusters are an interesting model of a mobile " pathogenicity island" not associated with a phage, transposon, or insertion element.