title: The F plasmid traY gene product binds DNA as a monomer or a dimer: structural and functional implications.
abstract: The F factor traY gene product (TraYp) is a site-specific DNA-binding protein involved in initiation of DNA transfer during bacterial conjugation. The sequence of TraYp exhibits a unique direct-repeat structure predicted to have a ribbon-helix-helix DNA-binding motif in each repeat unit. The stoichiometry of TraYp binding to DNA was determined to further support the hypothesis that TraYp is a member of the ribbon-helix-helix family of DNA-binding proteins. A glutathione-S-transferase-traY fusion protein was purified and shown to possess almost wild-type DNA-binding activity. DNA-binding experiments were performed in which the DNA ligand was incubated with either the fusion protein, the wild-type protein, or both. The results indicate that TraYp can bind DNA as a monomer or a dimer. Thus a TraYp monomer folds into a stable three-dimensional structure similar to that of a dimer of the ribbon-helix-helix proteins Arc or Mnt. A homology model of a TraYp monomer has been constructed using the co-crystal structure of Arc bound to DNA as a template to provide additional support for this conclusion. In addition, we have shown that an origin of the transfer-deletion mutant lacking approximately half of the TraYp-binding site can only be bound by a monomer of TraYp. The functional implications of this result are discussed.
authors.affiliation: Department of Biology CB#3280, University of North Carolina at Chapel Hill 27599-3280, USA.
authors.forename: W C
authors.initials: WC
authors.lastname: Nelson
authors.forename: S W
authors.initials: SW
authors.lastname: Matson
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D004269:DNA, Bacterial; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D005982:Glutathione Transferase / Q000235:genetics; D008958:Models, Molecular; D008969:Molecular Sequence Data; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism
chemical_list: D004269:DNA, Bacterial; D004268:DNA-Binding Proteins; D029968:Escherichia coli Proteins; D011993:Recombinant Fusion Proteins; C063238:traY protein, E coli; D005982:Glutathione Transferase