title: Role of calf thymus DNA-topoisomerase I phosphorylation on relaxation activity expression and on DNA-protein interaction. Role of DNA-topoisomerase I phosphorylation.
abstract: Calf thymus DNA-Topoisomerase I activity was found to be altered by changing in phosphorylation: it was completely inhibited upon dephosphorylation by alkaline phosphatase, but incubation with N II protein kinase and ATP restored the relaxation activity to a level higher than that observed prior to dephosphorylation. The calf thymus Topoisomerase I-mediated DNA cleavage, induced by camptothecin, also proved to be inhibited by dephosphorylation, which, apparently, stabilizes the initial enzyme-substrate complex. We conclude that: the native protein is partially phosphorylated, the phosphorylation involvement is essential for the activity expression and also for DNA-protein interaction, changes in the degree of phosphorylation might be involved in the regulation of DNA processing; that evokes some properties of chromatinic peptide models, which bind DNA only when phosphorylated and leads to the assumption that they represent the minimum functional substrate for N II protein kinase.
authors.affiliation: Department of Cell Biology, University of Camerino, Italy.
authors.forename: S
authors.initials: S
authors.lastname: Coderoni
authors.forename: M
authors.initials: M
authors.lastname: Paparelli
authors.forename: G L
authors.initials: GL
authors.lastname: Gianfranceschi
mesh_terms: D000818:Animals; D002166:Camptothecin / Q000494:pharmacology; D002417:Cattle; D004264:DNA Topoisomerases, Type I / Q000378:metabolism*; D004278:DNA, Superhelical / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D009690:Nucleic Acid Conformation; D010766:Phosphorylation; D010768:Phosphoserine / Q000032:analysis; D011494:Protein Kinases / Q000378:metabolism; D011499:Protein Processing, Post-Translational
chemical_list: D004278:DNA, Superhelical; D010768:Phosphoserine; D011494:Protein Kinases; D004264:DNA Topoisomerases, Type I; D002166:Camptothecin