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Tandem insertion sequence-like elements define the expression site for variable antigen genes of Borrelia hermsii
A G Barbour1, C J Carter, N Burman
1Department of Microbiology, University of Texas Health Science Center, San Antonio 78284.
Infection and Immunity
|January 1, 1991
Summary
Borrelia hermsii evades host immunity using variable surface proteins (VMPs). Researchers sequenced a key DNA region, revealing repeated elements that may control VMP gene switching.
Area of Science:
- Microbiology
- Molecular Biology
- Immunology
Background:
- Borrelia hermsii, a spirochete, employs multiphasic antigenic variation to evade host immune responses.
- Variable membrane proteins (VMPs) determine serotype specificity in B. hermsii.
- Antigenic variation is mediated by nonreciprocal recombination between linear plasmids, replacing silent vmp genes at a common expression site.
Purpose of the Study:
- To characterize the common upstream expression region of the vmp gene in Borrelia hermsii strain HS1.
- To identify DNA elements potentially involved in regulating vmp gene switching.
Main Methods:
- DNA sequencing of a 6.9 kb region upstream of the vmp gene promoter.
- Analysis of repeated DNA segments and their structures.
- Heteroduplex analysis to assess stem-and-loop formation potential.
Main Results:
- Sequencing revealed three imperfectly repeated 2-kb segments upstream of the vmp gene promoter.
- Each 2-kb segment contained 1-kb elements with inverted repeats, capable of forming stem-loop structures.
- These specific elements were not found elsewhere in the B. hermsii genome.
Conclusions:
- The identified repeated DNA elements in the vmp upstream region may play a role in the unidirectional switching of vmp genes.
- Understanding these elements provides insight into the mechanism of antigenic variation in Borrelia hermsii.