title: Supercoils in prokaryotic DNA restrained in vivo.
abstract: Cells of Escherichia coli containing the plasmid F were gamma-irradiated with various doses to introduce determined numbers of single-strand breaks in the F DNA. The cells were then incubated to permit repair of the breaks while DNA gyrase was inhibited with coumermycin to limit restoration of any relaxed supercoil. Repaired, covalently continuous F DNA was isolated and its superhelical density was measured by two different methods. Both indicated that a major part (50-60%) of the negative superhelical turns were maintained in the repaired molecules, suggesting that the supercoils are restrained in vivo.
mesh_terms: D049933:Aminocoumarins; D003374:Coumarins / Q000494:pharmacology; D004260:DNA Repair / Q000187:drug effects; D004269:DNA, Bacterial / Q000528:radiation effects; D004278:DNA, Superhelical / Q000528:radiation effects*; D004926:Escherichia coli; D005144:F Factor; D005720:Gamma Rays; D009690:Nucleic Acid Conformation / Q000528:radiation effects; D011758:Pyrroles / Q000494:pharmacology; D059005:Topoisomerase II Inhibitors
chemical_list: D049933:Aminocoumarins; D003374:Coumarins; D004269:DNA, Bacterial; D004278:DNA, Superhelical; D011758:Pyrroles; D059005:Topoisomerase II Inhibitors; C004628:coumermycin