title: Characterization of the DNA-binding properties of the origin-binding domain of simian virus 40 large T antigen by fluorescence anisotropy.
abstract: The affinity of the origin-binding domain (OBD) of simian virus 40 large T antigen for its cognate origin was measured at equilibrium using a DNA binding assay based on fluorescence anisotropy. At a near-physiological concentration of salt, the affinities of the OBD for site II and the core origin were 31 and 50 nM, respectively. Binding to any of the four 5'-GAGGC-3' binding sites in site II was only slightly weaker, between 57 and 150 nM. Although the OBD was shown previously to assemble as a dimer on two binding sites spaced by 7 bp, we found that increasing the distance between both binding sites by 1 to 3 bp had little effect on affinity. Similar results were obtained for full-length T antigen in absence of nucleotide. Addition of ADP-Mg, which promotes hexamerization of T antigen, greatly increased the affinity of full-length T antigen for the core origin and for nonspecific DNA. The implications of these findings for the assembly of T antigen at the origin and its transition to a non-specific DNA helicase are discussed.
authors.affiliation: Department of Biological Sciences, Boehringer Ingelheim (Canada) Ltd., Laval, Canada H7S 2G5.
authors.forename: S
authors.initials: S
authors.lastname: Titolo
authors.forename: E
authors.initials: E
authors.lastname: Welchner
authors.forename: P W
authors.initials: PW
authors.lastname: White
authors.forename: J
authors.initials: J
authors.lastname: Archambault
mesh_terms: D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001665:Binding Sites; D004261:DNA Replication; D004279:DNA, Viral / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019281:Dimerization; D005454:Fluorescence Polarization; D008969:Molecular Sequence Data; D018741:Replication Origin / Q000502:physiology*
chemical_list: D000952:Antigens, Polyomavirus Transforming; D004279:DNA, Viral; D004268:DNA-Binding Proteins