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J. Bacteriol., 01 1998, 350-358, Vol 180, No. 2
AW Williams and SC Straley
Yersinia pestis produces a set of virulence proteins (Yops and LcrV) that
are expressed at high levels and secreted by a type III secretion system
(Ysc) upon bacterium-host cell contact, and four of the Yops are
vectorially translocated into eukaryotic cells. YopD, YopB, and YopK are
required for the translocation process. In vitro, induction and secretion
occur at 37 degrees C in the absence of calcium. LcrH (also called SycD), a
protein required for the stability and secretion of YopD, had initially
been identified as a negative regulator of Yop expression. In this study,
we constructed a yopD mutation in both wild- type and secretion-defective
(ysc) Y. pestis to determine if the lcrH phenotype could be attributed to
the decreased stability of YopD. These mutants were constitutively induced
for expression of Yops and LcrV, despite the presence of the secreted
negative regulator LcrQ, demonstrating that YopD is involved in negative
regulation, regardless of a functioning Ysc system. Normally, secretion of
Yops and LcrV is blocked in the presence of calcium. The single yopD mutant
was not completely effective in blocking secretion: LcrV was secreted
equally well in the presence and absence of calcium, while there was
partial secretion of Yops in the presence of calcium. YopD is probably not
rate limiting for negative regulation, as increasing levels of YopD did not
result in decreased Yop expression. Overexpression of LcrQ in the yopD
mutant had no significant effect on Yop expression, whereas increased
levels of LcrQ in the parent resulted in decreased levels of Yops. These
results indicate that LcrQ requires YopD to function as a negative
regulator.
Copyright © 1998, American Society for Microbiology
YopD of Yersinia pestis plays a role in negative regulation of the low- calcium response in addition to its role in translocation of Yops [In Process Citation]
Department of Microbiology and Immunology, Albert B. Chandler Medical Center, University of Kentucky, Lexington 40536-0084, USA.
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