title: Effects of fluorodeoxyuridine and nalidixic acid on the activity of topoisomerase I in plasmodia of Physarum polycephalum.
abstract: 1. A regulatory coupling between the rate of cellular transcription and the activity of topoisomerase I was investigated in plasmodia of Physarum polycephalum treated with fluorodeoxyuridine or nalidixic acid. 2. Fluorodeoxyuridine at concentrations above 40 micrograms/ml lowered both the incorporation of [3H]uridine and the activity of topoisomerase I to 10% of corresponding control values. 3. Nalidixic acid, in the range of concentrations between 20-50 micrograms/ml did not inhibit the incorporation of [3H]uridine but lowered the activity of topoisomerase I by about half. 4. It is suggested that a coupling between the level of transcription and the activity of topoisomerase I in Physarum plasmodia involves only about a half of the topoisomerase I activity and is limited to transcription occurring on ribosomal genes.
authors.affiliation: Institute of Biochemistry, Warsaw University, Poland.
authors.forename: K
authors.initials: K
authors.lastname: Staron
authors.forename: B
authors.initials: B
authors.lastname: Kowalska-Loth
authors.forename: R M
authors.initials: RM
authors.lastname: Czerwiński
mesh_terms: D000818:Animals; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D005467:Floxuridine / Q000494:pharmacology*; D007700:Kinetics; D009268:Nalidixic Acid / Q000494:pharmacology*; D016839:Physarum polycephalum / Q000187:drug effects / Q000201:enzymology*; D012313:RNA / Q000096:biosynthesis; D014529:Uridine / Q000378:metabolism
chemical_list: D005467:Floxuridine; D009268:Nalidixic Acid; D012313:RNA; D004264:DNA Topoisomerases, Type I; D014529:Uridine