title: The redox state of the baculovirus single-stranded DNA-binding protein LEF-3 regulates its DNA binding, unwinding, and annealing activities.
abstract: The single-stranded (ss) DNA-binding protein LEF-3 of Autographa californica multinucleocapsid nucleopolyhedrovirus promoted Mg(2+)-independent unwinding of DNA duplexes and annealing of complementary DNA strands. The unwinding and annealing activities of LEF-3 appeared to act in a competitive manner and were determined by the ratio of protein to DNA. At subsaturating and saturating concentrations, LEF-3 promoted annealing, whereas it promoted unwinding at oversaturation of DNA substrates. The LEF-3 binding to ssDNA and unwinding activity were sensitive to redox agents and were inhibited by oxidation of thiol groups in LEF-3 with 1,1'-azobis(N,N-dimethylformamide) (diamide) or by modification with the thiol-conjugating agent N-ethylmaleimide. Both oxidation and alkylation increased the dissociation constant of the interaction with model oligonucleotides indicating a decrease in an intrinsic affinity of LEF-3 for ssDNA. These results proved that free thiol groups are essential both for LEF-3 interaction with ssDNA and for DNA unwinding. In contrast, oxidation or modification of thiol groups stimulated the annealing activity of LEF-3 partially due to suppression of its unwinding activity. Treatment of LEF-3 with the reducing agent dithiothreitol inhibited annealing, indicating association of this activity with the oxidized protein. Thus, the balance between annealing and unwinding activities of LEF-3 was determined by the redox state of protein with the oxidized state favoring annealing and the reduced state favoring unwinding. An LEF-3 mutant in which the conservative cysteine Cys(214) was replaced with serine showed both a decreased binding to DNA and a reduced unwinding activity, thus indicating that this residue might participate in the regulation of LEF-3 activities.
authors.affiliation: Department of Microbiology, Oregon State University, Corvallis, Oregon 97331-3804.
authors.forename: Victor S
authors.initials: VS
authors.lastname: Mikhailov
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Okano
authors.forename: George F
authors.initials: GF
authors.lastname: Rohrmann
mesh_terms: D000818:Animals; D004247:DNA / Q000737:chemistry / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000502:physiology*; D004229:Dithiothreitol / Q000494:pharmacology; D005033:Ethylmaleimide / Q000494:pharmacology; D010084:Oxidation-Reduction; D018411:Spodoptera; D014764:Viral Proteins / Q000502:physiology*
chemical_list: D004268:DNA-Binding Proteins; D014764:Viral Proteins; C094647:late expression factor 3, baculovirus; D004247:DNA; D005033:Ethylmaleimide; D004229:Dithiothreitol