Proteins conferred by the virulence-specifying plasmid of Agrobacterium tumefaciens C-58.

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Abstract
Membrane-associated and periplasmic proteins of A. tumefaciens C-58 were compared with those from avirulent (nontumorigenic) derivative strains by slab and 2-dimensional gel electrophoresis. Two proteins (Per-1 and Per-2), with a MW of 37,500 and 37,300, respectively, were detected in the supernatant fraction of cells of strain C-58 treated with EDTA and lysozyme in which a 117 mega dalton plasmid confers virulence on the organism. The same proteins are missing in an avirulent plasmid-free derivative of C-58. When this derivative is mated with C-58, the resulting transconjugants regain the large C-58 plasmid together with the restoration of virulence and the expression of Per-1 and Per-2 proteins. When the transconjugants were cured of their plasmid, they concomitantly lost their virulence and Per-1 and Per-2. The functional roles of these proteins are unknown, but they are associated with the outer membrane and periplasmic fraction of the Agrobacterium cell. If directly involved in tumorigenesis, these proteins are not the sole determinants of tumorigenicity because they are synthesized in an avirulent derivative of C-58 that carries a deletion in the plasmid in the region conferring the tumorigenic phenotype. The Per-1 and Per-2 proteins are probably plasmid-coded gene products. The possible roles of these proteins in specifying host range and host[plant]-cell attachment are also discussed.