title: Identification of a potent decatenating enzyme from Escherichia coli.
abstract: A topoisomerase has been purified from extracts of a topoisomerase I-deficient strain of Escherichia coli based solely on its ability to segregate pBR322 DNA replication intermediates in vitro. This enzyme rapidly decatenated multiply linked form II:form II DNA dimers to form II DNA, provided that the DNA substrate contained single-stranded regions. Efficient relaxation of negatively supercoiled DNA was observed when reaction mixtures were incubated at 52 degrees C, but not at 30 degrees C (the temperature at which decatenation was readily observed). This topoisomerase was insensitive to the DNA gyrase inhibitor norfloxacin and unaffected by antibody directed against topoisomerase I. Relaxation of a unique plasmid topoisomer revealed that this decatenase changed the linking number of the DNA in steps of one and was therefore a type 1 topoisomerase. The cleavage pattern of a fragment of single-stranded phi X174 DNA generated by this decatenase was virtually identical to that reported for topoisomerase III, the least characterized topoisomerase present in E. coli.
authors.affiliation: Graduate Program in Molecular Biology, Memorial Sloan-Kettering Cancer Center, New York, New York 10021.
authors.forename: R J
authors.initials: RJ
authors.lastname: DiGate
authors.forename: K J
authors.initials: KJ
authors.lastname: Marians
mesh_terms: D002872:Chromosome Deletion; D004247:DNA / Q000378:metabolism*; D004261:DNA Replication / Q000187:drug effects; D004264:DNA Topoisomerases, Type I / Q000032:analysis*; D004926:Escherichia coli / Q000201:enzymology*; D007527:Isoenzymes / Q000032:analysis*; D009643:Norfloxacin / Q000494:pharmacology; D059005:Topoisomerase II Inhibitors
chemical_list: D007527:Isoenzymes; D059005:Topoisomerase II Inhibitors; D004247:DNA; D004264:DNA Topoisomerases, Type I; D009643:Norfloxacin