Recq Helicase Stimulates Both DNA Catenation and Changes in DNA Topology by Topoisomerase III*
THE JOURNAL OF BIOLOGICAL CHEMISTRY Vol. 278, No. 43, Issue of October 24, pp. 42668–42678, 2003 © 2003 by The American Society for Biochemistry and Molecular Biology, Inc. Printed in U.S.A. RecQ Helicase Stimulates Both DNA Catenation and Changes in DNA Topology by Topoisomerase III* Received for publication, March 24, 2003, and in revised form, June 10, 2003 Published, JBC Papers in Press, August 8, 2003, DOI 10.1074/jbc.M302994200 Frank G. Harmon‡, Joel P. Brockman, and Stephen C. Kowalczykowski§ From the Division of Biological Sciences, Sections of Microbiology and of Molecular and Cellular Biology, Center for Genetics and Development, University of California, Davis, California 95616 Together, RecQ helicase and topoisomerase III (Topo which is premature aging and a predisposition to cancer (10). III) of Escherichia coli comprise a potent DNA strand Loss of BLM helicase function results in Bloom’s syndrome; in passage activity that can catenate covalently closed this case, afflicted individuals are highly susceptible to certain DNA (Harmon, F. G., DiGate, R. J., and Kowalczykowski, types of cancer (15). Mutations in the RECQ4 helicase are S. C. (1999) Mol. Cell 3, 611–620). Here we directly as- found in a subset of Rothmund-Thompson syndrome cases, a sessed the structure of the catenated DNA species disease that is also typified by a predisposition to malignancy formed by RecQ helicase and Topo III using atomic force (12, 18). microscopy. The images show complex catenated DNA Phenotypic analysis indicates that these helicases are species involving crossovers between multiple double- needed in their respective organisms to maintain the stability stranded DNA molecules that are consistent with full of the genome (for review, see Ref.
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