Research article

Characterisation of silent and active genes for a variable large protein of Borrelia recurrentis

Vincent Vidal^1,4 , Sally Cutler² , Ian G Scragg^1,5 , David JM Wright³ and Dominic Kwiatkowski¹

¹  Molecular Infectious Disease Group, Weatherall Institute of Molecular Medicine, Oxford

²  Department of Bacterial Diseases, Veterinary Laboratory Agency, Addlestone, Surrey

³  Cell & Molecular Biology, Imperial College of Science, Technology and Medicine, South Kensington campus, London

⁴  ISTAC SA, campus IPL, 1 rue du professeur Calmette, F59000, Lille, France

⁵  University of Dundee, Dundee, DD1 4HN, UK

author email corresponding author email

BMC Infectious Diseases 2002, 2:25doi:10.1186/1471-2334-2-25

Published:	14 October 2002

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 vlp1_{B. recurrentis A1} gene in both this and other isolates.

Results

This isolate was found to carry silent and expressed copies of the vlp1_{B. recurrentis A1} gene on plasmids of 54 kbp and 24 kbp respectively, whereas a different isolate, A17, had only the silent vlp1_{B. 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.

Conclusion

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.