Published in:
Open Access 01-12-2002 | Research article
Characterisation of silent and active genes for a variable large protein of Borrelia recurrentis
Published in: BMC Infectious Diseases | Issue 1/2002
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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.