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J. Biol. Chem., Vol. 277, Issue 18, 15333-15344, May 3, 2002
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From the Department of Microbiology, Moyne Institute of Preventive
Medicine, Trinity College Dublin, Dublin 2, Republic of Ireland
The VirB protein is a key regulator of virulence
gene expression in the facultative enteroinvasive pathogen
Shigella flexneri. While genetic evidence has shown that it
is required for activation of transcription of virulence genes located
on a 230-kb plasmid in this bacterium, hitherto, evidence that VirB is
a DNA-binding protein has been lacking. Although VirB shows extensive
homology to proteins involved in plasmid partitioning, it does not
resemble any known conventional transcription factor. Here we show for the first time that VirB binds to the promoter regions of the virulence genes in vivo. We also show that VirB forms
dimeric and higher oligomeric structures both in vivo and
in vitro and that this property is independent of DNA
binding. The oligomerization activity of VirB is distributed over two
domains: a leucine zipper-like motif and a carboxyl-terminal domain
likely to form triple coiled structures. VirB possesses a
helix-turn-helix motif, which is required for DNA binding. The
amino-terminal domain of the protein is also required for DNA binding
and virulence gene activation. The possibility that VirB requires a
co-factor for specific interaction with target promoters in
vivo is discussed.
Molecular Dissection of VirB, a Key Regulator of the Virulence
Cascade of Shigella flexneri*
,
*
This work was supported by European Union Training and
Mobility of Researchers Award ERBFMRXCT98-0164 and Enterprise Ireland Grant SC/99/432.The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
Present address: Groupe de Génétique des Biofilms,
Institut Pasteur, 25 rue du Dr. Roux, 75724 Paris, Cedex 15, France.
§
To whom correspondence should be addressed. Tel.: 353-1-608-2013;
Fax: 353-1-679-9294; E-mail: cjdorman@tcd.ie.
Copyright © 2002 by The American Society for Biochemistry and Molecular Biology, Inc.
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