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The F plasmid traY gene product binds DNA as a monomer or a dimer: structural and functional implications
Author(s) -
Nelson William C.,
Matson Steven W.
Publication year - 1996
Publication title -
molecular microbiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.857
H-Index - 247
eISSN - 1365-2958
pISSN - 0950-382X
DOI - 10.1111/j.1365-2958.1996.tb02638.x
Subject(s) - biology , dna , dimer , helix turn helix , monomer , dna binding site , helix (gastropod) , binding site , biochemistry , hmg box , dna binding protein , biophysics , crystallography , gene , chemistry , transcription factor , gene expression , promoter , ecology , organic chemistry , snail , polymer
Summary 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 gluta‐thione‐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.