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J. Biol. Chem., Vol. 278, Issue 37, 34925-34933, September 12, 2003

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The Escherichia coli RecQ Helicase Functions as a Monomer^*

Hou Qiang Xu , Eric Deprez, Ai Hua Zhang , Patrick Tauc, Moncef M. Ladjimi , Jean-Claude Brochon, Christian Auclair and Xu Guang Xi ¶

From the Laboratoire de Biotechnologies et Pharmacologie Génétique Appliquée CNRS UMR 8113, Ecole Normale Supérieure de Cachan, 61 Avenue du Président Wilson, 94235 Cachan cedex, France and UMR 7631, CNRS-Université P. & M. Curie, 96 Boulevard Raspail, 75006 Paris, France

The RecQ helicases belong to an important family of highly conserved DNA helicases that play a key role in chromosomal maintenance, and their defects have been shown to lead to several disorders and cancer in humans. In this work, the conformational and functional properties of the Escherichia coli RecQ helicase have been determined using a wide array of biochemical and biophysical techniques. The results obtained clearly indicate that E. coli RecQ helicase is monomeric in solution up to a concentration of 20 µM and in a temperature range between 4 and 37 °C. Furthermore, these properties are not affected by the presence of ATP, which is strictly required for the unwinding and translocating activity of the protein, or by its nonhydrolyzable analogue 5'-adenylyl-,-imidodiphosphate. Consistent with the structural properties, functional analysis shows that both DNA unwinding activity and single-stranded DNA-stimulated ATPase specific activity were independent of RecQ concentration. The monomeric state was further confirmed by the ATPase-deficient mutants of RecQ protein. The rate of unwinding was unchanged when the wild type RecQ helicase was mixed with the ATPase-deficient mutants, indicating that nonprotein-protein interactions were involved in the unwinding processes. Taken together, these results indicate that RecQ helicase functions as a monomer and provide new data on the structural and functional properties of RecQ helicase that may help elucidate its mechanism action.

Received for publication, April 7, 2003 , and in revised form, June 10, 2003.

^* This work was supported by the Centre National de la Recherche Scientifique. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

Supported by the China Scholarship Council.

^¶ To whom correspondence should be addressed. Tel.: 33-01-47-40-68-92; Fax: 33-01-47-40-76-71; E-mail: xi{at}lbpa.ens-cachan.fr.

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