Journal of Bacteriology, August 2001, p. 4588-4598, Vol. 183, No. 15
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.15.4588-4598.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.

andDepartment of Microbiology and Immunology, University of California Los Angeles School of Medicine, Los Angeles, California 90095
Received 1 February 2001/Accepted 27 April 2001
Yersinia enterocolitica target effector Yop proteins
into the cytosol of eukaryotic cells by a mechanism requiring the type III machinery. LcrG and LcrV have been suggested to fulfill essential functions during the type III targeting of effector Yops. It is reported here that knockout mutations of lcrG caused mutant
yersiniae to prematurely secrete Yops into the extracellular medium
without abolishing the type III targeting mechanism (Los phenotype
[loss of type III targeting specificity]). Knockout mutations in
lcrV reduced type III targeting of mutant yersiniae but did
not promote secretion into the extracellular medium (Not [no type III
targeting]). However, knockout mutations in both genes caused
lcrGV yersiniae to display a Los phenotype similar to
that of strains carrying knockout mutations in lcrG alone.
LcrG binding to LcrV resulted in the formation of soluble LcrGV
complexes in the bacterial cytoplasm. Membrane-associated,
bacterial-surface-displayed or -secreted LcrG could not be detected.
Most of LcrV was located in the bacterial cytoplasm; however, small
amounts were secreted into the extracellular medium. These data support
a model whereby LcrG may act as a negative regulator of type III
targeting in the bacterial cytoplasm, an activity that is modulated by
LcrG binding to LcrV. No support could be gathered for the hypothesis
whereby LcrG and LcrV may act as a bacterial surface receptor for host
cells, allowing effector Yop translocation across the eukaryotic plasma membrane.
Present address: Committee on Microbiology, The University of
Chicago, Chicago, IL 60637.
Present address: Department of Microbiology and Molecular
Genetics, Harvard Medical School, Boston, MA 02115.
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