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Antigenic variation by Borrelia hermsii occurs through recombination between extragenic repetitive elements on linear plasmids
Author(s) -
Dai Qiyuan,
Restrepo Blanca I.,
Porcella Stephen F.,
Raffel Sandra J.,
Schwan Tom G.,
Barbour Alan G.
Publication year - 2006
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.2006.05177.x
Subject(s) - biology , plasmid , genetics , gene , antigenic variation , locus (genetics) , insertion sequence , homology (biology) , transposable element , genome
Summary The relapsing fever agent Borrelia hermsii undergoes multiphasic antigenic variation through gene conversion of a unique expression site on a linear plasmid by an archived variable antigen gene. To further characterize this mechanism we assessed the repertoire and organization of archived variable antigen genes by sequencing ∼85% of plasmids bearing these genes. Most archived genes shared with the expressed gene a ≤ 62 nucleotide (nt) region, the upstream homology sequence (UHS), that surrounded the start codon. The 59 archived variable antigen genes were arrayed in clusters with 13 repetitive, 214 nt long downstream homology sequence (DHS) elements distributed among them. A fourteenth DHS element was downstream of the expression locus. Informative nucleotide polymorphisms in UHS regions and DHS elements were applied to the analysis of the expression site of relapse serotypes from 60 infected mice in a prospective study. For most recombinations, the upstream crossover occurred in the UHS’s second half, and the downstream crossover was in the DHS’s second half. Usually the closest archival DHS element was used, but occasionally a more distant DHS was employed. The downstream extragenic crossover site in B. hermsii contrasts with the downstream extragenic crossover site for antigenic variation in African trypanosomes.