title: Capsule loss in H. influenzae type b occurs by recombination-mediated disruption of a gene essential for polysaccharide export.
abstract: The capsulation locus cap in H. influenzae type b contains directly repeated segments of DNA flanking a bridge region. Here we show that this bridge region contains a gene, bexA, encoding a 24.7 kd protein essential for export of capsular polysaccharide. bexA is disrupted, with loss of part of its coding sequence, in the spontaneous reduction of the duplicated cap locus to single-copy that accompanies loss of capsule expression. The predicted amino acid sequence of BexA aligns significantly with that of MalK from E. coli and with HisP and OppD of S. typhimurium. Thus, polysaccharide export might occur via an energy-dependent transporter with similarities to those identified for the import of various substrates into Gram-negative bacteria, BexA being the "energizer" of the transporter.
authors.affiliation: Department of Pediatrics, Oxford University, England.
authors.forename: J S
authors.initials: JS
authors.lastname: Kroll
authors.forename: I
authors.initials: I
authors.lastname: Hopkins
authors.forename: E R
authors.initials: ER
authors.lastname: Moxon
mesh_terms: D000595:Amino Acid Sequence; D016667:Bacterial Capsules; D001426:Bacterial Proteins / Q000235:genetics*; D001428:Bacterial Vaccines; D001483:Base Sequence; D004269:DNA, Bacterial / Q000235:genetics; D005455:Fluorescent Antibody Technique; D005798:Genes, Bacterial; D018073:Haemophilus Vaccines; D006193:Haemophilus influenzae / Q000235:genetics* / Q000648:ultrastructure; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D009154:Mutation; D009693:Nucleic Acid Hybridization; D010641:Phenotype; D010957:Plasmids; D011135:Polysaccharides, Bacterial / Q000235:genetics* / Q000378:metabolism; D011995:Recombination, Genetic; D014169:Transformation, Bacterial
chemical_list: D001426:Bacterial Proteins; D001428:Bacterial Vaccines; D004269:DNA, Bacterial; D018073:Haemophilus Vaccines; C044237:Haemophilus influenzae type b polysaccharide vaccine; D011135:Polysaccharides, Bacterial