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Journal of Bacteriology, June 2008, p. 4242-4251, Vol. 190, No. 12
0021-9193/08/$08.00+0     doi:10.1128/JB.00336-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

ApoFnr Binds as a Monomer to Promoters Regulating the Expression of Enterotoxin Genes of Bacillus cereus{triangledown} ,{dagger}

Julia Esbelin,1 Yves Jouanneau,2 Jean Armengaud,3 and Catherine Duport1*

Université d'Avignon, UMR A408, Sécurité et Qualité des Produits d'Origine Végétale, and INRA, Avignon, F-84914, France,1 Laboratoire de Chimie et Biologie des Métaux, UMR 5249, CEA, DSV, iRTSV, CEA-Grenoble Cedex 09, F-38054, France,2 Laboratoire de Biochimie des Systèmes Perturbés, CEA-Marcoule, SBTN, BP17171, Bagnols-sur-Cèze Cedex, F-30207, France3

Received 7 March 2008/ Accepted 11 April 2008

Bacillus cereus Fnr is a member of the Crp/Fnr (cyclic AMP-binding protein/fumarate nitrate reduction regulatory protein) family of helix-turn-helix transcriptional regulators. It is essential for the expression of hbl and nhe enterotoxin genes independently of the oxygen tension in the environment. We studied aerobic Fnr binding to target sites in promoters regulating the expression of enterotoxin genes. B. cereus Fnr was overexpressed and purified as either a C-terminal His-tagged (FnrHis) fusion protein or an N-terminal fusion protein tagged with the Strep-tag (IBA BioTAGnology) (StrepFnr). Both recombinant Fnr proteins were produced as apoforms (clusterless) and occurred as mixtures of monomers and oligomers in solution. However, apoFnrHis was mainly monomeric, while apoStrepFnr was mainly oligomeric, suggesting that the His-tagged C-terminal extremity may interfere with oligomerization. The oligomeric state of apoStrepFnr was dithiothreitol sensitive, underlining the importance of a disulfide bridge for apoFnr oligomerization. Electrophoretic mobility shift assays showed that monomeric apoFnr, but not oligomeric apoFnr, bound to specific sequences located in the promoter regions of the enterotoxin regulators fnr, resDE, and plcR and the structural genes hbl and nhe. The question of whether apoFnr binding is regulated in vivo by redox-dependent oligomerization is discussed.

* Corresponding author. Mailing address: UMR A408, INRA, Site Agroparc, 84914 Avignon Cedex 9, France. Phone: 33 4 32 72 25 07. Fax: 33 4 32 72 24 92. E-mail: catherine.duport{at}univ-avignon.fr

{triangledown} Published ahead of print on 18 April 2008.

{dagger} Supplemental material for this article may be found at http://jb.asm.org/.

Journal of Bacteriology, June 2008, p. 4242-4251, Vol. 190, No. 12
0021-9193/08/$08.00+0     doi:10.1128/JB.00336-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Esbelin, J., Armengaud, J., Zigha, A., Duport, C. (2009). ResDE-Dependent Regulation of Enterotoxin Gene Expression in Bacillus cereus: Evidence for Multiple Modes of Binding for ResD and Interaction with Fnr. J. Bacteriol. 191: 4419-4426 [Abstract] [Full Text]  


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