title: Bacterial topoisomerase I and topoisomerase III relax supercoiled DNA via distinct pathways.
abstract: Escherichia coli topoisomerases I and III (Topo I and Topo III) relax negatively supercoiled DNA and also catenate/decatenate DNA molecules containing single-stranded DNA regions. Although these enzymes share the same mechanism of action and have similar structures, they participate in different cellular processes. In bulk experiments Topo I is more efficient at DNA relaxation, whereas Topo III is more efficient at catenation/decatenation, probably reflecting their differing cellular roles. To examine the differences in the mechanism of these two related type IA topoisomerases, single-molecule relaxation studies were conducted on several DNA substrates: negatively supercoiled DNA, positively supercoiled DNA with a mismatch and positively supercoiled DNA with a bulge. The experiments show differences in the way the two proteins work at the single-molecule level, while also recovering observations from the bulk experiments. Overall, Topo III relaxes DNA efficiently in fast processive runs, but with long pauses before relaxation runs, whereas Topo I relaxes DNA in slow processive runs but with short pauses before runs. The combination of these properties results in Topo I having an overall faster total relaxation rate, even though the relaxation rate during a run for Topo III is much faster.
authors.affiliation: Department of Molecular Biosciences, Northwestern University, Evanston, IL 60208, USA.
authors.forename: Ksenia
authors.initials: K
authors.lastname: Terekhova
authors.forename: Kathryn H
authors.initials: KH
authors.lastname: Gunn
authors.forename: John F
authors.initials: JF
authors.lastname: Marko
authors.forename: Alfonso
authors.initials: A
authors.lastname: Mondragón
mesh_terms: D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004278:DNA, Superhelical / Q000737:chemistry / Q000378:metabolism*; D004926:Escherichia coli / Q000201:enzymology*; D007700:Kinetics
chemical_list: D004278:DNA, Superhelical; D004264:DNA Topoisomerases, Type I