The mechanism of tumorigenesis by a bacterium, Agrobacterium tumefaciens, will be investigated. This bacterium contains a tumor-inducing (Ti) plasmid. DNA sequences complementary to a portion of the Ti plasmid DNA are found in the tumor cells. Using DNA:DNA hybridization, we will determine whether all tumor lines contain the same plasmid DNA sequences and, if not, which portions of the plasmid DNA are present in all tumor lines. The cytological localization of the plasmid DNA sequences in the tumor cells and whether the plasmid DNA sequences are integrated into the host cell DNA will be determined. The interaction between Agrobacterium tumefaciens and host cells in tissue culture will be examined. Attachment of the bacteria to the tissue culture cells has been obtained and will be studied. Attempts will be made to obtain the transfer of Ti plasmid DNA from the bacteria to the tissue culture cells and, if this is successful, to obtain the entire process of oncogenic transformation in tissue culture.