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Journal of Bacteriology, June 2008, p. 4252-4262, Vol. 190, No. 12
0021-9193/08/$08.00+0     doi:10.1128/JB.00328-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

YscP and YscU Switch the Substrate Specificity of the Yersinia Type III Secretion System by Regulating Export of the Inner Rod Protein YscI ^,

Sarah E. Wood,^1,2 Jin Jin,¹ and Scott A. Lloyd^1*

Department of Pediatrics, Center for Vaccine Development, University of Maryland at Baltimore, Baltimore, Maryland 21201,¹ Department of Food Science and Technology, University of Maryland Eastern Shore, Princess Anne, Maryland 21853²

Received 5 March 2008/ Accepted 8 April 2008

Pathogenic yersiniae utilize a type III secretion system to inject antihost factors, called Yops, directly into the cytosol of eukaryotic cells. The Yops are injected via a needle-like structure, comprising the YscF protein, on the bacterial surface. While the needle is being assembled, Yops cannot be secreted. YscP and YscU switch the substrate specificity of the secretion system to enable Yop export once the needle attains its proper length. Here, we demonstrate that the inner rod protein YscI plays a critical role in substrate specificity switching. We show that YscI is secreted by the type III secretion system and that YscI secretion by a yscP mutant is abnormally elevated. Furthermore, we show that mutations in the cytoplasmic domain of YscU reduce YscI secretion by the yscP null strain. We also demonstrate that mutants expressing one of three forms of YscI (those with mutations Q84A, L87A, and L96A) secrete substantial amounts of Yops yet exhibit severe defects in needle formation. In the absence of YscP, mutants with the same changes in YscI assemble needles but are unable to secrete Yops. Together, these results suggest that the formation of the inner rod, not the needle, is critical for substrate specificity switching and that YscP and YscU exert their effects on substrate export by controlling the secretion of YscI.

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* Corresponding author. Mailing address: Department of Pediatrics, Center for Vaccine Development, University of Maryland at Baltimore, 685 W. Baltimore St., Baltimore, MD 21201. Phone: (410) 706-5336. Fax: (410) 706-6205. E-mail: slloyd{at}medicine.umaryland.edu

Published ahead of print on 18 April 2008.

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

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Journal of Bacteriology, June 2008, p. 4252-4262, Vol. 190, No. 12
0021-9193/08/$08.00+0     doi:10.1128/JB.00328-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

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