title: The cap region of topoisomerase I binds to sites near both ends of simian virus 40 T antigen.
abstract: Two independent binding sites on simian virus 40 (SV40) T antigen for topoisomerase I (topo I) were identified. One was mapped to the N-terminal domain (residues 83 to 160) by a combination of enzyme-linked immunosorbent assays (ELISAs) and glutathione S-transferase (GST) pull-down assays performed with various T antigen deletion mutants. The second was mapped to the C-terminal domain (residues 602 to 708). The region in human topo I that binds to both sites in T antigen was identified by ELISAs, GST pull-down assays, and double-hexamer binding assays with topo I deletion mutants. This region corresponds to a distinct domain on topo I known as the cap region that maps from residues 175 to 433. By combining these data with information about the structure of T-antigen double hexamers associated with origin DNA, we propose that the cap region of topo I associates specifically with both ends of the double hexamer bound to the SV40 origin to initiate DNA replication.
authors.affiliation: Department of Biological Sciences, University of Delaware, Newark, DE 19716-2590, USA.
authors.forename: Rupa
authors.initials: R
authors.lastname: Roy
authors.forename: Pamela
authors.initials: P
authors.lastname: Trowbridge
authors.forename: Zheng
authors.initials: Z
authors.lastname: Yang
authors.forename: James J
authors.initials: JJ
authors.lastname: Champoux
authors.forename: Daniel T
authors.initials: DT
authors.lastname: Simmons
mesh_terms: D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000737:chemistry / Q000378:metabolism*; D001665:Binding Sites; D004261:DNA Replication; D004264:DNA Topoisomerases, Type I / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D013539:Simian virus 40 / Q000276:immunology*
chemical_list: D000952:Antigens, Polyomavirus Transforming; D004264:DNA Topoisomerases, Type I