Single-molecule study of DNA unlinking by eukaryotic and prokaryotic type-II topoisomerases
- Laboratoire de Physique Statistique, Ecole Normale Supérieure, Unité Mixte de Recherche 8550 Centre National de la Recherche Scientifique, 24 Rue Lhomond, 75231 Paris Cedex 05, France; and Département de Biologie, Ecole Normale Supérieure, 46 Rue d'Ulm, 75231 Paris Cedex 05, France
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Edited by Kiyoshi Mizuuchi, National Institutes of Health, Bethesda, MD, and approved June 13, 2003 (received for review March 18, 2003)
Abstract
Type-II topoisomerases are responsible for untangling DNA during replication by removing supercoiled and interlinked DNA structures. Using a single-molecule micromanipulation setup, we follow the real-time decatenation of two mechanically braided DNA molecules by Drosophila melanogaster topoisomerase (Topo) II and Escherichia coli Topo IV. Although Topo II relaxes left-handed (L) and right-handed (R-) braids similarly at a rate of ≈2.9 s– 1, Topo IV has a marked preference for L-braids, which it relaxes completely and processively at a rate of ≈2.4 s– 1. However, Topo IV can unlink R-braids at about half that rate when they supercoil to form L-plectonemes. These results imply that the preferred substrate for unlinking by Topo IV has the symmetry of an L-crossing and shed new light on the decatenation of daughter strands during DNA replication, which are usually assumed to be linked in an R-braid.
Footnotes
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↵ * To whom correspondence should be addressed. E-mail: gilles.charvin{at}lps.ens.fr.
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This paper was submitted directly (Track II) to the PNAS office.
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Abbreviations: Topo, topoisomerase; T, transport; G, gate; L-, left-handed; R-, right-handed.
- Copyright © 2003, The National Academy of Sciences
