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Journal of Bacteriology, January 2002, p. 224-232, Vol. 184, No. 1
0021-9193/01/$04.00+0     DOI: 10.1128/JB.184.1.224-232.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

The ATP-Dependent Lon Protease of Salmonella enterica Serovar Typhimurium Regulates Invasion and Expression of Genes Carried on Salmonella Pathogenicity Island 1

Akiko Takaya,1 Toshifumi Tomoyasu,1 Akane Tokumitsu,1 Mizue Morioka,2 and Tomoko Yamamoto1*

Department of Microbiology and Molecular Genetics, Graduate School of Pharmaceutical Sciences, Chiba University, Chiba 263-8522,1 Department of Biological Sciences, Graduate School of Science, The University of Tokyo,Tokyo 113-0033, Japan2

Received 13 August 2001/ Accepted 1 October 2001

An early step in the pathogenesis of Salmonella enterica serovar Typhimurium infection is bacterial penetration of the intestinal epithelium. Penetration requires the expression of invasion genes found in Salmonella pathogenicity island 1 (SPI1). These genes are controlled in a complex manner by regulators in SPI1, including HilA and InvF, and those outside SPI1, such as two-component regulatory systems and small DNA-binding proteins. We report here that the expression of invasion genes and the invasive phenotype of S. enterica serovar Typhimurium are negatively regulated by the ATP-dependent Lon protease, which is known to be a major contributor to proteolysis in Escherichia coli. A disrupted mutant of lon was able to efficiently invade cultured epithelial cells and showed increased production and secretion of three identified SPI1 proteins, SipA, SipC, and SipD. The lon mutant also showed a dramatic enhancement in transcription of the SPI1 genes hilA, invF, sipA, and sipC. The increases ranged from 10-fold to almost 40-fold. It is well known that the expression of SPI1 genes is also regulated in response to several environmental conditions. We found that the disruption of lon does not abolish the repression of hilA and sipC expression by high-oxygen or low-osmolarity conditions, suggesting that Lon represses SPI1 gene expression by a regulatory pathway independent of these environmental signals. Since HilA is thought to function as a central regulator of SPI1 gene expression, it is speculated that Lon may regulate SPI1 gene expression by proteolysis of putative factors required for activation of hilA expression.


* Corresponding author. Mailing address: Department of Microbiology and Molecular Genetics, Graduate School of Pharmaceutical Sciences, Chiba University, 1-33 Yayoi-cho, Inage-ku, Chiba 263-8522, Japan. Phone: (81) 43-290-2928. Fax: (81) 43-290-2929. E-mail: tomoko-y{at}p.chiba-u.ac.jp.


Journal of Bacteriology, January 2002, p. 224-232, Vol. 184, No. 1
0021-9193/01/$04.00+0     DOI: 10.1128/JB.184.1.224-232.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.




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