title: Characterisation of silent and active genes for a variable large protein of Borrelia recurrentis.
abstract: BACKGROUND
  We report the characterisation of the variable large protein (vlp) gene expressed by clinical isolate A1 of Borrelia recurrentis; the agent of the life-threatening disease louse-borne relapsing fever.
  
  
  METHODS
  The major vlp protein of this isolate was characterised and a DNA probe created. Use of this together with standard molecular methods was used to determine the location of the vlp1B. recurrentis A1 gene in both this and other isolates.
  
  
  RESULTS
  This isolate was found to carry silent and expressed copies of the vlp1B. recurrentis A1 gene on plasmids of 54 kbp and 24 kbp respectively, whereas a different isolate, A17, had only the silent vlp1B. recurrentis A17 on a 54 kbp plasmid. Silent and expressed vlp1 have identical mature protein coding regions but have different 5' regions, both containing different potential lipoprotein leader sequences. Only one form of vlp1 is transcribed in the A1 isolate of B. recurrentis, yet both 5' upstream sequences of this vlp1 gene possess features of bacterial promoters.
  
  
  CONCLUSIONS
  Taken together these results suggest that antigenic variation in B. recurrentis may result from recombination of variable large and small protein genes at the junction between lipoprotein leader sequence and mature protein coding region. However, this hypothetical model needs to be validated by further identification of expressed and silent variant protein genes in other B. recurrentis isolates.
authors.affiliation: Molecular Infectious Disease Group, Weatherall Institute of Molecular Medicine, Oxford, UK. vfvidal@yahoo.fr
authors.forename: Vincent
authors.initials: V
authors.lastname: Vidal
authors.forename: Sally
authors.initials: S
authors.lastname: Cutler
authors.forename: Ian G
authors.initials: IG
authors.lastname: Scragg
authors.forename: David J M
authors.initials: DJ
authors.lastname: Wright
authors.forename: Dominic
authors.initials: D
authors.lastname: Kwiatkowski
mesh_terms: D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics*; D001898:Borrelia / Q000235:genetics*; D005786:Gene Expression Regulation; D015964:Gene Expression Regulation, Bacterial; D020868:Gene Silencing; D006801:Humans; D010957:Plasmids / Q000235:genetics
chemical_list: D000942:Antigens, Bacterial; D001425:Bacterial Outer Membrane Proteins; D001426:Bacterial Proteins; C121437:Vsp protein, bacterial