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Journal of Bacteriology, December 2005, p. 7890-7900, Vol. 187, No. 23
0021-9193/05/$08.00+0     doi:10.1128/JB.187.23.7890-7900.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Vibrio cholerae ToxT Independently Activates the Divergently Transcribed aldA and tagA Genes

Jeffrey H. Withey1 and Victor J. DiRita1,2*

Unit for Laboratory Animal Medicine,1 Department of Microbiology and Immunology, University of Michigan Medical School, Ann Arbor, Michigan 48109-06142

Received 11 May 2005/ Accepted 15 September 2005

The Vibrio cholerae ToxT regulon includes the genes encoding cholera toxin (CT) and the toxin-coregulated pilus (TCP), which are the major virulence factors required for causing cholera disease and colonizing the upper small intestine of the host, respectively. The genes encoding CT, ctxAB, and the genes encoding the components of the TCP, tcpA to tcpJ, are organized within operons, upstream of which are DNA binding sites for the transcriptional activator ToxT. ToxT is a member of the large AraC/XylS family of transcriptional regulators and also activates transcription of five other genes whose roles in V. cholerae pathogenesis, if any, are poorly understood. acfA and acfD are divergently transcribed genes required for efficient colonization of the intestine. Transcriptional activation of acfA and acfD requires a pair of central ToxT binding sites in an inverted-repeat configuration for ToxT-directed transcription of both genes. tcpI has an unknown role in pathogenesis. aldA and tagA are divergently transcribed genes that also have unknown roles in pathogenesis. In this study, we map the aldA and tagA promoters and identify the ToxT binding sites upstream of each gene. Our results suggest that two ToxT binding sites in an inverted-repeat configuration are required for ToxT-directed transcription of tagA and that a single ToxT binding site is required for ToxT-directed transcription of aldA. Furthermore, to direct transcription of tagA and aldA, ToxT uses independent binding regions upstream of each gene, in contrast to what we previously found for the divergently transcribed acfA and acfD genes, which share ToxT binding sites between the two genes.

* Corresponding author. Mailing address: Unit for Laboratory Animal Medicine, University of Michigan Medical School, Ann Arbor, MI 48109-0614. Phone: (734) 936-1707. Fax: (734) 764-3562. E-mail: vdirita{at}umich.edu.

Journal of Bacteriology, December 2005, p. 7890-7900, Vol. 187, No. 23
0021-9193/05/$08.00+0     doi:10.1128/JB.187.23.7890-7900.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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