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J. Bacteriol., 02 1997, 1211-1218, Vol 179, No. 4
C Baron, YR Thorstenson and PC Zambryski
VirB9 and VirB7 are essential components of the putative VirB membrane
channel required for transfer of the T-complex from Agrobacterium
tumefaciens into plants. In this report, we present a biochemical analysis
of their interaction and cellular localization. A comparison of relative
electrophoretic mobilities under nonreducing and reducing conditions
suggested that they form thiol-sensitive complexes with other proteins.
Two-dimensional gel electrophoresis identified one complex as a heterodimer
of VirB9 and VirB7 covalently linked by a disulfide bond, as well as VirB7
homodimers and monomers. Immunoprecipitation with VirB9-specific antiserum
isolated the heterodimeric VirB9-VirB7 complex. Incubation with reducing
agent split the complex into its constituent VirB9 and VirB7, which further
confirmed linkage via cysteine residues. The interaction between VirB9 and
VirB7 also was observed in the yeast two-hybrid system. Membrane attachment
of VirB9-VirB7 may be conferred by lipoprotein modification, since labeling
with [3H]palmitic acid in A. tumefaciens verified that VirB7 is a
lipoprotein associated with VirB9. VirB9 and VirB7 showed equal
distribution between inner and outer membranes, in accord with their
proposed association with the transmembrane VirB complex.
Copyright © 1997, American Society for Microbiology
The lipoprotein VirB7 interacts with VirB9 in the membranes of Agrobacterium tumefaciens
Department of Plant and Microbial Biology, University of California at Berkeley, 94720, USA.
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