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Journal of Bacteriology, July 1999, p. 4198-4204, Vol. 181, No. 14
Department of Microbiology, Molecular
Biology, and Biochemistry, University of Idaho, Moscow, Idaho 83843
Received 6 January 1999/Accepted 30 April 1999
Temperature has a pleiotropic effect on Yersinia
enterocolitica gene expression. Temperature-dependent phenotypes
include the switching between two type III protein secretion systems, flagellum biosynthesis (
0021-9193/99/$04.00+0
Copyright © 1999, American Society for Microbiology. All rights reserved.
The Yersinia enterocolitica pYV
Virulence Plasmid Contains Multiple Intrinsic DNA Bends Which Melt
at 37°C


30°C) and virulence plasmid-encoded Yop secretion (37°C). The mechanism by which temperature exerts this change in genetic programming is unclear; however, altered gene expression by temperature-dependent changes in DNA topology has been
implicated. Here, we present evidence that the Y. enterocolitica virulence plasmid, pYV, undergoes a conformational
transition between 30 and 37°C. Using a simplified two-dimensional,
single-gel assay, we show that pYV contains multiple regions of
intrinsic curvature, including virF, the positive activator
of virulence genes. These bends are detectable at 30°C but melt at
37°C, the temperature at which the cells undergo phenotypic
switching. We also show that pACYC184, a plasmid used as a reporter of
temperature-induced changes in DNA supercoiling, has a single region of
intrinsic bending detected by our assay. Topoisomers of pACYC184, with
and without this bend, isolated from Y. enterocolitica were
resolved by using chloroquine gels. The single bend has a dramatic
influence on temperature-dependent DNA supercoiling. These data suggest that the Y. enterocolitica pYV plasmid may undergo a
conformational change at the host temperature due to melting of DNA
bends followed by compensatory adjustments in superhelical density.
Hence, changes in DNA topology may be the temperature-sensing mechanism
for virulence gene expression in Y. enterocolitica and
other enteric pathogens.
*
Corresponding author. Mailing address: Department of
Microbiology, Molecular Biology, & Biochemistry, University of Idaho, Moscow, ID 83843. Phone: (208) 885-7884. Fax: (208) 885-6518. E-mail:
sminnich{at}uidaho.edu.
Present address: Department of Biochemistry, University of British
Columbia, Vancouver, BC V67-1Z3 Canada.
Present address: Shandong Institute of Biology, Jinan 250014, People's Republic of China.
§
Present address: Laboratory of Persistent Viral Diseases, Rocky
Mountain Laboratories, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Hamilton, MT 59840.
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