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J. Bacteriol., 02 1997, 1307-1316, Vol 179, No. 4
ML Nilles, AW Williams, E Skrzypek and SC Straley
Yersinia pestis contains a virulence plasmid, pCD1, that encodes many
virulence-associated traits, such as the Yops (Yersinia outer proteins) and
the bifunctional LcrV, which has both regulatory and antihost functions. In
addition to LcrV and the Yops, pCD1 encodes a type III secretion system
that is responsible for Yop and LcrV secretion. The Yop-LcrV secretion
mechanism is believed to regulate transcription of lcrV and yop operons
indirectly by controlling the intracellular concentration of a secreted
repressor. The activity of the secretion mechanism and consequently the
expression of LcrV and Yops are negatively regulated in response to
environmental conditions such as Ca2+ concentration by LcrE and,
additionally, by LcrG, both of which have been proposed to block the
secretion mechanism. This block is removed by the absence of Ca2+ or by
contact with eukaryotic cells, and some Yops are then translocated into the
cells. Regulation of LcrV and Yop expression also is positively affected by
LcrV. Previously, LcrG was shown to be secreted from bacterial cells when
the growth medium lacks added Ca2+, although most of the LcrG remains cell
associated. In the present study, we showed that the cell-associated LcrG
is cytoplasmically localized. We demonstrated that LcrG interacts with LcrV
to form a heterodimeric complex by using chemical cross-linking and
copurification of LcrG and LcrV. Additionally, we found that small amounts
of LcrV and YopE can be detected in periplasmic fractions isolated by cold
osmotic shock and spheroplast formation, indicating that their secretion
pathway is accessible to the periplasm or to these procedures for obtaining
periplasmic fractions. We propose that the cytoplasmically localized LcrG
blocks the Yop secretion apparatus from the cytoplasmic side and that LcrV
is required to remove the LcrG secretion block to yield full induction of
Yop and LcrV secretion and expression.
Copyright © 1997, American Society for Microbiology
Yersinia pestis LcrV forms a stable complex with LcrG and may have a secretion-related regulatory role in the low-Ca2+ response
Department of Microbiology and Immunology, University of Kentucky, Lexington 40536-0084, USA.
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