title: Variable antigen genes of the relapsing fever agent Borrelia hermsii are activated by promoter addition.
abstract: Borrelia hermsii, an agent of relapsing fever, avoids the host's immune response by means of multiphasic antigenic variation. Serotype specificity is determined by variable antigens called the Vmp lipoproteins. Through recombination between linear plasmids a formerly silent vmp gene replaces another vmp gene at a telomeric expression locus. We examined strain HS1 borreliae before and after a switch from serotype 7 to serotype 21. The nucleotide sequences of 5' regions of silent and expressed vmp7 and vmp21 were determined. Silent and active vmp7 and vmp21 genes shared a block of homologous sequences surrounding their 5' ends. Sequences upstream of silent vmp7 and vmp21 genes lacked the promoter and substantially differed from each other. In this antigenic switch a vmp gene was activated by a recombination that placed it downstream of a promoter.
authors.affiliation: Department of Microbiology, University of Texas Health Science Center, San Antonio 78284.
authors.forename: A G
authors.initials: AG
authors.lastname: Barbour
authors.forename: N
authors.initials: N
authors.lastname: Burman
authors.forename: C J
authors.initials: CJ
authors.lastname: Carter
authors.forename: T
authors.initials: T
authors.lastname: Kitten
authors.forename: S
authors.initials: S
authors.lastname: Bergström
mesh_terms: D000940:Antigenic Variation / Q000235:genetics*; D000942:Antigens, Bacterial / Q000235:genetics* / Q000276:immunology; D000954:Antigens, Surface / Q000235:genetics* / Q000276:immunology; D001425:Bacterial Outer Membrane Proteins; D001483:Base Sequence; D001898:Borrelia / Q000235:genetics* / Q000276:immunology; D004269:DNA, Bacterial; D015964:Gene Expression Regulation, Bacterial; D008969:Molecular Sequence Data; D011401:Promoter Regions, Genetic; D011995:Recombination, Genetic; D015183:Restriction Mapping; D012689:Sequence Homology, Nucleic Acid; D012703:Serotyping
chemical_list: D000942:Antigens, Bacterial; D000954:Antigens, Surface; D001425:Bacterial Outer Membrane Proteins; D004269:DNA, Bacterial; C067934:VMP7 protein, Borrelia hermsii; C067935:VMP21 antigen, Borrelia