Association of the virD2 protein with the 5' end of T strands in Agrobacterium tumefaciens

The soil bacterium Agrobacterium tumefaciens can incite tumors in many dicotyledonous plants by transferring a portion (T-DNA) of its Ti plasmid into susceptible plant cells. The T-DNA is flanked by border sequences that serve as recognition sites for specific cleavage by an endonuclease that comprises two virD-encoded proteins (VirD1 and VirD2). After cleavage, both double-stranded, nicked T-DNA molecules and single-stranded T-DNA molecules (T strands) were present. We have determined that a protein is tightly associated with, and probably covalently attached to, the 5' end of the T strands. Analysis of deletion derivatives in Escherichia coli, immunoprecipitation, and a procedure combining immunoblot and nucleic acid hybridization data identified this protein as the gene product of virD2.