The genomes of the Kirsten and Harvey murine sarcoma viruses have been found to contaan limited portions of the genome of the leukemia virus with which they were first isolated, along with a specific set of rat cellular sequences. These rat cellular sequences appear to be unrelated to any rat type-C leukemia virus. A major objective of this research is the elucidation of the functions of those rat sequences which were incorporated in the murine sarcoma virus genomes. Assaying for this RNA by molecular hybridization to the DNA product of Kirsten sarcoma virus, we shall characterize this RNA as to its intracellular location, size, and stability in normal neoplastic rat cells. We shall also investigate the variables which influence expression of this RNA, particularly concerning cell growth and possible hormonal relationships. By hybridization to the DNA product of rat leukemia virus, expression of endogenous leukemia virus RNA will also be monitored throughout these studies, which should help further characterize the nature and functions of the endogenous rat leukemia viruses. Toward a section objective, proposed studies are directed at determining if the apparent pattern of specific cellular sequences recombined with type-C leukemia virus sequences also occurs in spontaneous tumors, particularly in rat leukemias. As assayed by molecular hybridization of tissue RNA to the reverse transcription DNA products of Kirsten Sarcoma virus and of a rat leukemia virus, we will characterize the sedimentation behavior and electrophoretic mobility of both types of sequences in tumor and normal tissues. Affinity chromatographic techniques will be further used to test the recombination possibility. Together these studies are aimed at defining the function of the components of the Kirsten murine sarcoma virus genome, and determining if the apparent transduction of cellular genetic information seen in this sarcoma virus is relevant to events occurring in spontaneous tumors.