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J. Bacteriol., Mar 1996, 1420-1429, Vol 178, No. 5
EP Johnson, AR Strom and DR Helinski
The parDE operon, located within the 3.2-kb stabilization region of plasmid
RK2, encodes antitoxin (ParD) and toxin (ParE) proteins that stabilize the
maintenance of this broad-host-range plasmid via a postsegregational
killing mechanism. A ParE protein derivative, designated ParE', was
purified by construction of a fusion protein, GST- ParE, followed by
glutathione-agarose binding and cleavage of the fusion protein. ParE' has
three additional amino acids on the N terminus and a methionine residue in
place of the native leucine residue. The results of glutathione-agarose
affinity binding and glutaraldehyde cross-linking indicate that ParE'
exists as a dimer in solution and that it binds to the dimeric form of ParD
to form a tetrameric complex. The formation of this complex is presumably
responsible for the ability of ParD to neutralize ParE toxin activity.
Previous studies demonstrated that the parDE operon is autoregulated as a
result of the binding of the ParD protein to the parDE promoter. ParE' also
binds to the parDE promoter but only in the presence of the autoregulatory
ParD protein. ParE', in the presence or absence of the ParD protein, does
not bind to any other part of the 3.2-kb stabilization region. The binding
of the ParE' protein to ParD did not alter the DNase I footprint pattern
obtained as a result of ParD binding to the parDE promoter. The role of
ParE in binding along with ParD to the promoter, if any, remains unclear.
Copyright © 1996, American Society for Microbiology
Plasmid RK2 toxin protein ParE: purification and interaction with the ParD antitoxin protein
Department of Biology, University of California at San Diego, La Jolla 92037-0634, USA.
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