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Infection and Immunity, October 1998, p. 4656-4668, Vol. 66, No. 10
Department of Microbiology and Immunology,
Medical College of Virginia of Virginia Commonwealth University,
Richmond, Virginia 23298-0678
Received 27 April 1998/Returned for modification 26 June
1998/Accepted 10 July 1998
A series of related genes that are flanked at their 5' ends by a
conserved upstream sequence element called the upstream homology box
(UHB) have been identified in Borrelia burgdorferi. These genes have been referred to as the UHB or erp gene family.
We previously demonstrated that among a limited number of B. burgdorferi isolates, the UHB gene family is variable in
composition and organization. Prior to this report the UHB gene family
in other species of the B. burgdorferi sensu lato complex
had not been studied, and if this family is important in the
pathogenesis or biology of the Lyme disease spirochetes, then a wide
distribution among species and isolates of the B. burgdorferi sensu lato complex would be expected. To assess this,
we screened for the UHB element by Southern hybridization and
determined its restriction fragment length polymorphism (RFLP)
patterns. The UHB element was found to be carried by all B. burgdorferi sensu lato complex species tested (B. burgdorferi, B. garinii, B. afzelii,
B. japonica, B. valaisiana sp. nov., and B. andersonii), but the RFLP patterns varied widely at both
the inter- and intraspecies levels. Variation in both the number and size of the hybridizing restriction fragments was evident. PCR analyses
also revealed the presence of polymorphic, ospE-related alleles in many isolates. Sequence analyses identified the molecular basis of the polymorphisms as being primarily insertions and deletions. Sequence variation and the insertions and deletions were found to be
clustered in two distinct domains (variable domains 1 and 2). In many
isolates variable domain 1 is flanked by direct repeat elements, some
as long as 38 bp. Computer analyses of the deduced amino acid sequences
encoded within variable domain 1 predict them to be hydrophilic,
surface exposed, and antigenic. The analyses conducted here suggest
that the UHB gene family, as evidenced by the variable UHB RFLP
patterns, is not evolutionarily stable and that the polymorphic
ospE alleles are derived from a common ancestral gene which
has been modified through mutation or recombination events. The
characterization of ospE-related genes of the UHB gene
family among B. burgdorferi sensu lato species will prove important in attempts to construct a model for UHB gene family organization and in deciphering the role of the UHB gene family in the
biology and pathogenesis of the Lyme disease spirochetes.
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Genetic Divergence and Evolutionary Instability in
ospE-Related Members of the Upstream Homology Box Gene
Family in Borrelia burgdorferi Sensu Lato Complex
Isolates
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, Sanger Hall, Medical College of Virginia of Virginia Commonwealth University, 1101 East Marshall St., Richmond, VA 23298-0678. Phone: (804) 828-3779. Fax: (804) 828-9946. E-mail: rmarconi{at}hsc.vcu.edu.
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