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Journal of Bacteriology, April 2009, p. 2069-2076, Vol. 191, No. 7
0021-9193/09/$08.00+0     doi:10.1128/JB.01577-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Involvement of the Cra Global Regulatory Protein in the Expression of the iscRSUA Operon, Revealed during Studies of Tricarballylate Catabolism in Salmonella enterica ^,

Jeffrey A. Lewis, Jeffrey M. Boyd, Diana M. Downs, and Jorge C. Escalante-Semerena^*

Department of Bacteriology, University of Wisconsin—Madison, 6478 Microbial Sciences Building, 1550 Linden Drive, Madison, Wisconsin 53706-1521

Received 6 November 2008/ Accepted 6 January 2009

In Salmonella enterica, tricarballylate (Tcb) catabolism requires function of TcuB, a membrane-bound protein that contains [4Fe-4S] clusters and heme. TcuB transfers electrons from reduced flavin adenine dinucleotide in the Tcb dehydrogenase (TcuA) to electron acceptors in the membrane. We recently showed that functions needed to assemble [Fe-S] clusters (i.e., the iscRSUA-hscBA-fdx operon) compensate for the lack of ApbC during growth of an apbC strain on Tcb. ApbC had been linked to [Fe-S] cluster metabolism, and we showed that an apbC strain had decreased TcuB activity. Here we report findings that expand our understanding of the regulation of expression of the iscRSUA genes in Salmonella enterica. We investigated why low levels of glucose or other saccharides restored growth of an apbC strain on Tcb. Here we report the following findings. (i) A 1 mM concentration of glucose, fructose, ribose, or glycerol restores growth of an apbC strain on Tcb. (ii) The saccharide effect results in increased levels of TcuB activity. (iii) The saccharide effect depends on the global regulatory protein Cra. (iv) Putative Cra binding sites are present in the regulatory region of the iscRSUA operon. (v) Cra protein binds to all three sites in the iscRSUA promoter region in a concentration-dependent fashion. To our knowledge, this is the first report of the involvement of Cra in [Fe-S] cluster assembly.

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* Corresponding author. Mailing address: Department of Bacteriology, University of Wisconsin—Madison, 6478 Microbial Sciences Building, 1550 Linden Drive, Madison WI 53706-1521. Phone: (608) 262-7379. Fax: (608) 265-7909. E-mail: escalante{at}bact.wisc.edu

Published ahead of print on 9 January 2009.

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

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Journal of Bacteriology, April 2009, p. 2069-2076, Vol. 191, No. 7
0021-9193/09/$08.00+0     doi:10.1128/JB.01577-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.