Bacterial topoisomerase i and topoisomerase III relax supercoiled DNA via distinct pathways

Ksenia Terekhova, Kathryn H. Gunn, John F. Marko, Alfonso Mondragón*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

30 Scopus citations


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.

Original languageEnglish (US)
Pages (from-to)10432-10440
Number of pages9
JournalNucleic acids research
Issue number20
StatePublished - Nov 2012

ASJC Scopus subject areas

  • Genetics


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