title: Bacillus cereus DNA topoisomerase I and IIIalpha: purification, characterization and complementation of Escherichia coli TopoIII activity.
abstract: The Bacillus cereus genome possesses three type IA topoisomerase genes. These genes, encoding DNA topoisomerase I and IIIalpha (bcTopo I, bcTopo IIIalpha), have been cloned into T7 RNA polymerase-regulated plasmid expression vectors and the enzymes have been overexpressed, purified and characterized. The proteins exhibit similar biochemical activity to their Escherichia coli counterparts, DNA topoisomerase I and III (ecTopo I, ecTopo III). bcTopo I is capable of efficiently relaxing negatively supercoiled DNA in the presence of Mg2+ but does not possess an efficient DNA decatenation activity. bcTopo IIIalpha is an active topoisomerase that is capable of relaxing supercoiled DNA at a broad range of Mg2+ concentrations; however, its DNA relaxation activity is not as efficient as that of bcTopo I. In addition, bcTopo III is a potent DNA decatenase that resolves oriC-based plasmid replication intermediates in vitro. Interestingly, bcTopo I and bcTopo IIIalpha are both able to compensate for the loss of ecTopo III in E.coli cells that lack ecTopo I. In contrast, ecTopo I cannot substitute for ecTopo III under these conditions.
authors.affiliation: Department of Pharmaceutical Sciences, School of Pharmacy, University of Maryland, Baltimore, MA, USA.
authors.forename: Zhiyu
authors.initials: Z
authors.lastname: Li
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Hiasa
authors.forename: Russell
authors.initials: R
authors.lastname: DiGate
mesh_terms: D001409:Bacillus cereus / Q000201:enzymology* / Q000235:genetics; D001483:Base Sequence; D001665:Binding Sites; D004247:DNA / Q000737:chemistry / Q000378:metabolism; D004264:DNA Topoisomerases, Type I / Q000235:genetics / Q000302:isolation & purification / Q000378:metabolism*; D004277:DNA, Single-Stranded / Q000378:metabolism; D004926:Escherichia coli / Q000201:enzymology; D005816:Genetic Complementation Test; D008969:Molecular Sequence Data; D013379:Substrate Specificity
chemical_list: D004277:DNA, Single-Stranded; D004247:DNA; D004264:DNA Topoisomerases, Type I