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Journal of Bacteriology, June 2009, p. 3811-3821, Vol. 191, No. 12
0021-9193/09/$08.00+0     doi:10.1128/JB.00002-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Functional Domains of ExsA, the Transcriptional Activator of the Pseudomonas aeruginosa Type III Secretion System {triangledown}

Evan D. Brutinel, Christopher A. Vakulskas, and Timothy L. Yahr*

Department of Microbiology, University of Iowa, Iowa City, Iowa

Received 2 January 2009/ Accepted 12 April 2009

The opportunistic pathogen Pseudomonas aeruginosa utilizes a type III secretion system (T3SS) to evade phagocytosis and damage eukaryotic cells. Transcription of the T3SS regulon is controlled by ExsA, a member of the AraC/XylS family of transcriptional regulators. These family members generally consist of an ~100-amino acid carboxy-terminal domain (CTD) with two helix-turn-helix DNA binding motifs and an ~200-amino acid amino-terminal domain (NTD) with known functions including oligomerization and ligand binding. In the present study, we show that the CTD of ExsA binds to ExsA-dependent promoters in vitro and activates transcription from ExsA-dependent promoters both in vitro and in vivo. Despite possessing these activities, the CTD lacks the cooperative binding properties observed for full-length ExsA at the PexsC promoter. In addition, the CTD is unaffected by the negative regulatory activity of ExsD, an inhibitor of ExsA activity. Binding studies confirm that ExsD interacts directly with the NTD of ExsA. Our data are consistent with a model in which a single ExsA molecule first binds to a high-affinity site on the PexsC promoter. Protein-protein interactions mediated by the NTD then recruit an additional ExsA molecule to a second site on the promoter to form a complex capable of stimulating wild-type levels of transcription. These findings provide important insight into the mechanisms of transcriptional activation by ExsA and inhibition of ExsA activity by ExsD.

* Corresponding author. Mailing address: University of Iowa, 540B Eckstein Medical Research Building, Iowa City, IA 52242-1101. Phone: (319) 335-9688. Fax: (319) 335-8228. E-mail: tim-yahr{at}uiowa.edu

{triangledown} Published ahead of print on 17 April 2009.

Journal of Bacteriology, June 2009, p. 3811-3821, Vol. 191, No. 12
0021-9193/09/$08.00+0     doi:10.1128/JB.00002-09
Copyright © 2009, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Vakulskas, C. A., Brady, K. M., Yahr, T. L. (2009). Mechanism of Transcriptional Activation by Pseudomonas aeruginosa ExsA. J. Bacteriol. 191: 6654-6664 [Abstract] [Full Text]  


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