The overall goal of this proposal is to investigate the activation of oncogenes in radiation carcinogenesis. Recently, our laboratory has identified an activated k-ras oncogene in x-ray transformed 10T 1/2 cells in culture. Evidence suggests that the k-ras oncogene has been activated by somatic mutation. We are proposing to extend these results to investigate whether other types of radiation induced-transformation activate the same oncogene, and by the same mechanism of activation, in 10T 1/2 clones transformed by UV-light, fission-spectrum neutrons and x-rays. Our second aim is to extend the results of k-ras activation in x-ray transformed cells. We will identify oncogenic activation in a x-irradiation induced fibrosarcoma in C3H mouse and compare these results to the activated k-ras in x-ray transformed C3H cells (10T 1/2) in culture. These results will suggest whether x-ray transformation activates the same oncogene (and mechanism of activation) in vitro and in vivo. Additionally, we are proposing to investigate oncogenic activation in x-ray induced immortalization of primary rat embryo cells in culture associated with, and without, tumorigenicity. These studies will more clearly define the earlier events (immortalization) of radiation induced tumorigenesis. The third aim of this proposal is to investigate the timing of k-ras oncogene activation after x-irradiation of 10T 1/2 cells. The research in this proposal will be accomplished using the techniques of 1) hybridization for DNA and RNA analysis, 2) DNA transfection experiments, 3) molecular cloning by construction of genomic libraries, and 4) DNA sequencing. The results will identify activated oncogenes and define the molecular mechanisms of activation in the multistep events of radiation carcinogenesis. The knowledge gained from these investigations may eventually lead to methods of treatment and prevention of radiation induced neoplasia in man.