Binding of the regulatory protein VirG to the phased signal sequences upstream from virulence genes on the hairy-root-inducing plasmid.

The VirG protein is a positive regulator for the virulence genes of which expression is induced by a plant factor, and is essential for Agrobacterium pathogenicity on dicotyledonous plants. The VirG protein of the hairy-root-inducing plasmid A4 was overproduced in Escherichia coli cells, and purified to homogeneity. DNase I footprinting experiments revealed that the purified VirG protein was bound to the upstream region of virulence genes including the phased vir box sequences, which had been presumed to be the VirG recognition signal from the sequence analysis. In dimethyl sulfate footprinting, the VirG protein specifically protected the guanine residues within every vir box sequence. It was concluded that the VirG protein was bound to the phased vir box sequences from the major groove along one side of double-helical DNA.