THE VIRD2 PROTEIN OF AGROBACTERIUM-TUMEFACIENS CARRIES NUCLEAR-LOCALIZATION SIGNALS IMPORTANT FOR TRANSFER OF T-DNA TO PLANTS

Agrobacterium tumefaciens is able to transfer a piece of DNA, the T-DN A, to the nucleus of the plant cell. The VirD2 protein is required for the production of the T-DNA, it is tightly linked to the T-DNA and it is thought to direct it to the plant genome. Two nuclear localization signals (NLS), one in the N-terminal part and one in the C-terminal p art of the VirD2 protein, have been shown to be able to target marker proteins to the plant nucleus. Here we analyze nuclear entry of the T- DNA complex using a new and very sensitive assay for T-DNA transfer. W e show that optimal T-DNA transfer requires the VirD2 NLS located in t he C-terminal part of the protein, whereas mutations in the N-terminal NLS coding sequence seem to have no effect on T-DNA transfer.