title: Interaction between the N-terminus of human topoisomerase I and SV40 large T antigen.
abstract: We have attempted to identify human topoisomerase I-binding proteins in order to gain information regarding the cellular roles of this protein and the cytotoxic mechanisms of the anticancer drug camptothecin, which specifically targets topoisomerase I. In the course of this work we identified an interaction between the N-terminus of human topoisomerase I and the SV40 T antigen that is detectable in vitro using both affinity chromatography and co-immunoprecipitation. Additional results indicate that this interaction does not require intermediary DNA or stoichiometric quantities of other proteins. Furthermore, the interaction is detectable in vivo using a yeast two-hybrid assay. Two binding sites for T antigen are apparent on the topoisomerase I protein: one consisting of amino acids 1-139, the other present in the 383-765 region of the protein. Interestingly, nucleolin, which binds the 166-210 region of topoisomerase I, is able to bind an N-terminal fragment of topoisomerase I concurrently with T antigen. Taken together with our prior identification of nucleolin as a topoisomerase I-binding protein, the current results suggest that helicase-binding is a major role of the N-terminus of human topoisomerase I and that the resultant helicase-topoisomerase complex may function as a eukaryotic gyrase.
authors.affiliation: Department of Pharmacology, Robert Wood Johnson Medical School and the Cancer Institute of New Jersey, University of Medicine and Dentistry of New Jersey, New Brunswick, NJ 08901, USA.
authors.forename: P
authors.initials: P
authors.lastname: Haluska
authors.forename: A
authors.initials: A
authors.lastname: Saleem
authors.forename: T K
authors.initials: TK
authors.lastname: Edwards
authors.forename: E H
authors.initials: EH
authors.lastname: Rubin
mesh_terms: D000952:Antigens, Polyomavirus Transforming / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D001665:Binding Sites; D002846:Chromatography, Affinity; D003001:Cloning, Molecular; D004247:DNA / Q000096:biosynthesis / Q000737:chemistry; D004265:DNA Helicases / Q000737:chemistry / Q000378:metabolism; D004261:DNA Replication; D004264:DNA Topoisomerases, Type I / Q000737:chemistry* / Q000302:isolation & purification / Q000378:metabolism*; D004259:DNA-Directed DNA Polymerase / Q000737:chemistry / Q000378:metabolism; D017930:Genes, Reporter; D006801:Humans; D008957:Models, Genetic; D008958:Models, Molecular; D009690:Nucleic Acid Conformation; D011487:Protein Conformation; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D013539:Simian virus 40 / Q000378:metabolism*; D001616:beta-Galactosidase / Q000096:biosynthesis
chemical_list: D000952:Antigens, Polyomavirus Transforming; D011993:Recombinant Fusion Proteins; D004247:DNA; D004259:DNA-Directed DNA Polymerase; D001616:beta-Galactosidase; D004265:DNA Helicases; D004264:DNA Topoisomerases, Type I