Rauscher murine leukemia virus 35S subunit genomic RNA was translated in a cell-free extract derived from mouse cells grown in culture and initiation factors obtained from rabbit reticulocytes. The endogenous protein synthesis activity was reduced 10-20 fold by treatment with a calcium ion-dependent nuclease. The viral specific protein product consisted of polypeptides with molecular weights of 60,000, 68,000, 75,000 and 200,000. The 68,000 protein was the major protein product made in this in vitro system. All of these polypeptides were specifically recognized by monospecific antisera prepared against the major viral structural protein p30. The 68,000 protein had the methionine containing tryptic peptides of the mature p30 protein. These in vitro viral specific translation products are similar in size and properties to viral specific precursor polyproteins found in viral infected cells. The goals for the coming year are: To characterize the 68,000 dalton, 75,000 dalton, 80,000 dalton and the 180,000-200,000 dalton polypeptides made in response to th 3S Rauscher leukemia virus RNA; to characterize intracellular virus-specific messenger RNA from Rauscher leukemia virus infected cells; to isolate and characterize initiation peptides(s) formed in vitro in protein synthesizing cell extracts in response to Rauscher leukemia virus genomic RNA; and to translate Moloney murine sarcoma virus-specific subunit RNA (approximately 30S) in cell-free systems, and characterize the sarcoma virus-specific translation product and compare and contrast it to Moloney leukemia virus subunit RNA (approximately 35S) translation product.