title: Distamycin inhibition of topoisomerase I-DNA interaction: a mechanistic analysis.
abstract: Inhibition of eukaryotic DNA topoisomerase I by the minor groove binding ligand, distamycin A, was investigated. Low concentrations of the ligand selectively prevented catalytic action at a high affinity topoisomerase I binding sequence. A restriction enzyme protection assay indicated that the catalytic cycle was blocked at the binding step. Distamycin binding sites on DNA were localized by hydroxyl radical footprinting. A strongly preferred site mapped to a homopolymeric (dA).(dT)-tract partially included in the essential topoisomerase I binding region. Mutational elimination of the stable helix curvature associated with this ligand binding site demonstrated that (i) the intrinsic bend was unessential for efficient binding of topoisomerase I, and (ii) distamycin inhibition did not occur by deformation of a stable band. Alternative modes of inhibition are discussed.
authors.affiliation: Department of Molecular Biology and Plant Physiology, University of Aarhus, Denmark.
authors.forename: U H
authors.initials: UH
authors.lastname: Mortensen
authors.forename: T
authors.initials: T
authors.lastname: Stevnsner
authors.forename: S
authors.initials: S
authors.lastname: Krogh
authors.forename: K
authors.initials: K
authors.lastname: Olesen
authors.forename: O
authors.initials: O
authors.lastname: Westergaard
authors.forename: B J
authors.initials: BJ
authors.lastname: Bonven
mesh_terms: D000818:Animals; D001483:Base Sequence; D001665:Binding Sites; D004247:DNA / Q000378:metabolism*; D004264:DNA Topoisomerases, Type I / Q000378:metabolism; D004214:Distamycins / Q000494:pharmacology*; D008969:Molecular Sequence Data; D009154:Mutation; D009690:Nucleic Acid Conformation; D011067:Poly dA-dT / Q000378:metabolism; D011758:Pyrroles / Q000494:pharmacology*; D059004:Topoisomerase I Inhibitors
chemical_list: D004214:Distamycins; D011758:Pyrroles; D059004:Topoisomerase I Inhibitors; D011067:Poly dA-dT; D004247:DNA; D004264:DNA Topoisomerases, Type I