This Article Full Text Full Text (PDF) Other Versions of this Article: JB.00905-07v1 189/19/6882    most recent Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Reprints and Permissions Copyright Information Books from ASM Press MicrobeWorld Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Olekhnovich, I. N. Articles by Kadner, R. J. Search for Related Content PubMed PubMed Citation Articles by Olekhnovich, I. N. Articles by Kadner, R. J.

 Previous Article  |  Next Article 

Journal of Bacteriology, October 2007, p. 6882-6890, Vol. 189, No. 19
0021-9193/07/$08.00+0     doi:10.1128/JB.00905-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Role of Nucleoid-Associated Proteins Hha and H-NS in Expression of Salmonella enterica Activators HilD, HilC, and RtsA Required for Cell Invasion

Igor N. Olekhnovich^* and Robert J. Kadner

Department of Microbiology, University of Virginia School of Medicine, Charlottesville, Virginia 22908-0734

Received 8 June 2007/ Accepted 23 July 2007

The coordinate expression of Salmonella enterica invasion genes on Salmonella pathogenicity island 1 is under the control of the complex circuits of regulation that involve the AraC/XylS family transcriptional activators HilD, HilC, and RtsA and nucleoid-associated proteins. Single-copy transcription fusions were used to assess the effects of nucleoid-associated proteins Hha and H-NS on hilD, hilC, and rtsA expression. The data show that all three genes, hilD, hilC, and rtsA, were repressed by H-NS and/or Hha. The repression of rtsA was the highest among tested genes. The level of rtsA-lac was equally elevated in hns and hha mutants and was further enhanced in the hns hha double mutant under low-osmolarity conditions. Electrophoretic mobility shift experiments showed that H-NS and Hha directly bind to the rtsA promoter. In addition to the negative control that was exerted by H-NS/Hha under low-osmolarity conditions, the homologous virulence activators HilD, HilC, and RtsA (Hil activators) induced rtsA-lac expression in a high-salt medium. A DNase footprinting assay of the rtsA promoter revealed one common DNA-binding site for all three Hil activators centered at position –54 relative to the transcriptional start site. In the absence of Hha and H-NS, however, osmoregulation of the rtsA promoter was lost, and Hil activators were not required for rtsA transcription. These results taken together suggest that the HilD, HilC, and RtsA proteins induce the transcription of the rtsA promoter by counteracting H-NS/Hha-mediated repression.

Published ahead of print on 3 August 2007.

Deceased 7 August 2005.

This article has been cited by other articles:

• Stoebel, D. M., Free, A., Dorman, C. J. (2008). Anti-silencing: overcoming H-NS-mediated repression of transcription in Gram-negative enteric bacteria. Microbiology 154: 2533-2545 [Abstract] [Full Text]  
• Mizusaki, H., Takaya, A., Yamamoto, T., Aizawa, S.-I. (2008). Signal Pathway in Salt-Activated Expression of the Salmonella Pathogenicity Island 1 Type III Secretion System in Salmonella enterica Serovar Typhimurium. J. Bacteriol. 190: 4624-4631 [Abstract] [Full Text]  
• Ellermeier, J. R., Slauch, J. M. (2008). Fur Regulates Expression of the Salmonella Pathogenicity Island 1 Type III Secretion System through HilD. J. Bacteriol. 190: 476-486 [Abstract] [Full Text]