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Journal of Bacteriology, December 2000, p. 6638-6644, Vol. 182, No. 23
Department of
Microbiology1 and Department of
Medicine,2 University of Washington,
Seattle, Washington 98195
Received 27 June 2000/Accepted 18 September 2000
A wide variety of gram-negative bacteria utilize a specialized
apparatus called the type III secretion system (TTSS) to translocate virulence factors directly into the cytoplasm of eukaryotic cells. These translocated effectors contribute to the pathogen's ability to
infect and replicate within plant and animal hosts. The amino terminus
of effector proteins contains sequences that are necessary and
sufficient for both secretion and translocation by TTSS. Portions of
these sequences contain binding sites for type III chaperones, which
facilitate efficient secretion and translocation of specific effectors
through TTSS. In this study, we have utilized the yeast two-hybrid
assay to identify protein-protein interactions between effector and
chaperone proteins encoded within Salmonella pathogenicity island 1 (SPI-1). Several interactions were identified including a
novel interaction between the effector protein, SspA (SipA), and a
putative chaperone, InvB. InvB was demonstrated to bind to the amino
terminus of SspA in the bacterial cytoplasm. Furthermore, InvB acts as
a type III chaperone for the efficient secretion and translocation of
SspA by SPI-1. InvB also permitted translocation of SspA through the
SPI-2 TTSS, indicating that it is an important regulator in the
recognition of SspA as a target of TTSS. Finally, it was determined
that InvB does not alter the transcription of sspA but that
its absence results in reduced SspA protein levels in Salmonella
enterica serovar Typhimurium.
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
InvB Is a Type III Secretion Chaperone Specific
for SspA
*
Corresponding author. Mailing address: Departments of
Medicine and Microbiology, University of Washington, Health Sciences Building, Box 357710, Seattle, WA 98195. Phone: (206) 616-5107. Fax:
(206) 616-4295. E-mail: millersi{at}u.washington.edu.
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