title: The genetics of encapsulation in Haemophilus influenzae.
abstract: In Haemophilus influenzae type b (Hib) strains the cap locus with very few exceptions contains an unstable direct repeat of approximately 17 kb of DNA flanking an approximately 1-kb bridge region containing the gene bexA. Each repeat contains genes necessary for polysaccharide synthesis, export, and surface expression, with BexA a critical component of the polysaccharide exporter. Only rare Hib strains have been identified in which cap lacks a direct repeat, though this is the norm for non-b serotypes. Examination of the ends of this single-copy locus shows that cap has the structure of a compound transposon: Copies of the insertion element IS1016 flank the gene cluster. This gives strains the capacity to amplify genes at cap by unequal homologous recombination. The cap duplication in Hib strains--subserving augmented production of polysaccharide--has apparently arisen in this way and become fixed in the population through deletion of one copy of bexA.
authors.affiliation: Institute of Molecular Medicine, Oxford University, John Radcliffe Hospital, United Kingdom.
authors.forename: J S
authors.initials: JS
authors.lastname: Kroll
mesh_terms: D016667:Bacterial Capsules / Q000737:chemistry / Q000235:genetics*; D002876:Chromosomes, Bacterial / Q000737:chemistry; D004251:DNA Transposable Elements; D004269:DNA, Bacterial / Q000737:chemistry; D006193:Haemophilus influenzae / Q000737:chemistry / Q000235:genetics*; D006801:Humans; D005810:Multigene Family; D012091:Repetitive Sequences, Nucleic Acid
chemical_list: D004251:DNA Transposable Elements; D004269:DNA, Bacterial