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Nucleic Acids Research 2004 32(12):3537-3545; doi:10.1093/nar/gkh683
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Published online 6 July 2004

Nucleic Acids Research, Vol. 32 No. 12 © Oxford University Press 2004; all rights reserved

Reverse gyrase has heat-protective DNA chaperone activity independent of supercoiling

Martin Kampmann* and Daniela Stock

MRC Laboratory of Molecular Biology, Hills Road, Cambridge CB2 2QH, UK

* To whom correspondence should be addressed at present address: The Rockefeller University, 1230 York Avenue, New York, NY 10021, USA.Tel: +1 212 3278101; Fax: +1 212 3277880; Email: Martin.Kampmann{at}rockefeller.edu

Received March 8, 2004; Revised May 5, 2004; Accepted June 16, 2004

Hyperthermophilic organisms must protect their constituent macromolecules from heat-induced degradation. A general mechanism for thermoprotection of DNA in active cells is unknown. We show that reverse gyrase, the only protein that is both specific and common to all hyperthermophiles, reduces the rate of double-stranded DNA breakage ~8-fold at 90°C. This activity does not require ATP hydrolysis and is independent of the positive supercoiling activity of the enzyme. Reverse gyrase has a minor nonspecific effect on the rate of depurination, and a major specific effect on the rate of double-strand breakage. Using electron microscopy, we show that reverse gyrase recognizes nicked DNA and recruits a protein coat to the site of damage through cooperative binding. Analogously to molecular chaperones that assist unfolded proteins, we found that reverse gyrase prevents inappropriate aggregation of denatured DNA regions and promotes correct annealing. We propose a model for a targeted protection mechanism in vivo in which reverse gyrase detects damaged DNA and acts as a molecular splint to prevent DNA breakage in the vicinity of the lesion, thus maintaining damaged DNA in a conformation that is amenable to repair.


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