The VirD2 protein of A. tumefaciens contains a C-terminal bipartite nuclear localization signal: Implications for nuclear uptake of DNA in plant cells

Here we show that the VirD2 protein of A. tumefaciens functions as a nuclear localizing protein in plant cells. The nuclear localization signal of VirD2 consists of two regions containing 4-5 basic amino acids (KRPR and RKRER), located within the C-terminal 34 amino acids. These regions conform to the KR/KXR/K motif required for numerous nuclear localized nonplant eukaryotic proteins. Each region independently directs a β-glucuronidase reporter protein to the nucleus; however, both regions are necessary for maximum efficiency. VirD2 has been shown to be tightly bound to the 5′ end of the single-stranded DNA transfer intermediate, T-strand, transferred from Agrobacterium to the plant cell genome. The present results imply that T-strand transport to the plant nucleus is mediated by the tightly attached VirD2 protein via an import pathway common to higher eukaryotes.