Control of DNA Supercoiling during Thermal Stress in Hyperthermophilic Archaea
Purificación LÓPEZ-GARCIA and Patrick FORTERRE
IGM, Université Paris-Sud, Bât 409, ORSAY cedex , France
Poster displayed during the '98 thermophiles meeting, held in
Brest, France, September 6-11 1998.
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Purificación LÓPEZ-GARCÍA* and Patrick FORTERRE
Institut de Génétique et Microbiologie, Université Paris-Sud, bât. 409, 91405 Orsay Cedex, France
Environmental changes such as temperature or osmolarity shifts can affect DNA supercoiling. Many promoters, specially those of genes coding for proteins involved in the stress response, are indeed sensitive to DNA supercoiling. Accordingly, variations in DNA conformation have been suggested to trigger the stress response by switching on some genes while silencing others.
In mesophilic bacteria, where DNA is negatively supercoiled, heat or cold shocks are accompanied by transient modifications of DNA topology. Gyrase, introducing negative supercoils, the DNA-binding protein HU and the chaperone DnaK regulate these changes. In hyperthermophilic archaea, where plasmid DNA is found from relaxed to positively supercoiled, important transient topological changes are observed as well (1). Plasmids from different strains of Sulfolobales (kingdom Crenarchaeota) and Thermococcales (Euryarchaota) exhibit a sharp linking number (Lk) increase during heat shock (80 to 85 or 92°C) and a decrease during cold shock (80 to 65°C). A subsequent recovery of values closer to the initial state is observed.
We have initiated a study aiming to identify the regulators of DNA topology involved in the thermal stress response in these organisms. In general, DNA-topoisomerases and small DNA-binding proteins (histones and histone-like) are the main intracellular components of the machinery controlling DNA conformation. In Sulfolobus strains, the candidate proteins to regulate DNA topology during thermal shocks are essentially reverse gyrase, a hyperthermophile-specific enzyme introducing positive supercoils in DNA, the relaxing Topoisomerase VI, and Sso7d, a small and abundant DNA-binding protein which unwinds DNA. Immunological analysis does not reveal quantitative changes of these proteins during shocks. Analysis of crude extract activities rather suggests that DNA topological dynamics during heat and cold shock is controlled by specific global topoisomerase activities and DNA-protein binding at different temperatures.
(1) López-García, P., and Forterre, P. (1997) Mol. Microbiol., 23, 1267-1279.
Keywords: DNA Supercoiling, Hyperthermophilic Archaea, Thermal stress
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