Single-molecule study of DNA unlinking by eukaryotic and prokaryotic type-II topoisomerases.
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 approximately 2.9 s-1, Topo IV has a marked preference for L-braids, which it relaxes completely and processively at a rate of approximately 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.
Charvin
G
G
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. gilles.charvin@lps.ens.fr
Bensimon
D
D
Croquette
V
V
D000818:Animals; D004247:DNA / Q000737:chemistry* / Q000378:metabolism*; D027101:DNA Topoisomerase IV / Q000378:metabolism; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004278:DNA, Superhelical / Q000737:chemistry / Q000378:metabolism; D004331:Drosophila melanogaster / Q000201:enzymology; D004926:Escherichia coli / Q000201:enzymology; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D011387:Prokaryotic Cells; D013237:Stereoisomerism
D004278:DNA, Superhelical; D004247:DNA; D027101:DNA Topoisomerase IV; D004250:DNA Topoisomerases, Type II