Single-molecule study of DNA unlinking by eukaryotic and prokaryotic type-II topoisomerases

Publication Type:

Journal Article

Source:

PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA, NATL ACAD SCIENCES, Volume 100, Number 17, 2101 CONSTITUTION AVE NW, WASHINGTON, DC 20418 USA, p.9820-9825 (2003)

DOI:

10.1073/pnas.1631550100

Keywords:

DECATENATION; DOUBLE HELIX; ELASTICITY; ESCHERICHIA-COLI; GYRASE; IV; REPLICATION; ROLES; SEGREGATION; SUPERCOILED DNA

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 approximate to2.9 s(-1), Topo IV has a marked preference for L-braids, which it relaxes completely and processively at a rate of approximate to2.4 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.