The long range objective of our laboratory is to understand the molecular basis of crown gall, a neoplastic disease of dicotyledonous plants. At present, it is known that tumor formation involves a stable transfer of genetic information, the Ti plasmid T-DNA, from Agrobacterium tumefaciens to the plant cells. Further, the evidence suggests that the Ti plasmid sequences referred to as the "common-DNA" have a central role in oncogenesis: all the Ti plasmids have either a highly conserved or related version of the common-DNA; these sequences are part of the T-DNA in all tumor lines examined; they are transcribed in the tumor tissues and mutations introduced into this region of the Ti plasmid affect tumor formation. Clearly, a detailed knowledge of the transcription and possible translation products of the T-DNA, in particular the common-DNA, should lead to a better understanding of the molecular basis of this tumorigenic process. We therefore propose to initiate a detailed study of T-DNA expression in the A6S/2 tumor line. We will determine the number, size and accurate map positions of the T-DNA transcripts (by "Northern blotting" and S1 nuclease mapping experiments), which transcripts are involved in tumor formation (using site specific mutagenesis), the DNA sequence of the "oncogene(s)" (by the Maxam-Gilbert technique) and whether the oncogene(s) codes for a protein(s) synthesized in the tumor tissues. The study of crown gall tumorigenesis is "health-related"; it is concerned with the basic mechanisms of tumor formation. Further, our studies should eventually contribute to an understanding of the roles of hormones in regulated cell growth (normal plant tissues require phytohormones for growth while crown gall tumor tissues are hormone-independent) and the mechanisms of eucaryotic gene expression (we should eventually learn what DNA sequences constitute effective promotors of transcription in plants). The study of crown gall has already revealed that procaryotes can induce cancer in eucaryotes and that genetic recombination between procaryotes and eucaryotes is a naturally occurring phenomenon. It is anticipated that the continued study of crown gall will yield additional insight into basic biological processes.