The influence of in vivo expression of protein products of recombinant env genes on MuLV mediated leukemogenesis will be explored. A correlation will be sought between specific aspects of the synthesis and processing of env gene products and the ability of AKR dualtropic MCF viruses to induce preleukemic changes and leukemia development in AKR mice. A detailed biochemical analysis of the types of env gene products expressed and the kinetics of their processing will be carried out in virus infected fibroblasts and in thymocytes and leukemia cells. Ecotropic virus induced leukemias will be examined for expression of protein products of recombinant env genes. The env gene products expressed in ecotropic virus infected fibroblasts and in leukemias induced by those viruses will be compared by a sensitive peptide mapping procedure. The influence of the host cell on the synthesis of glycosylated and nonglycosylated gag gene polyproteins will be examined. Gag gene polyproteins expressed in virus infected fibroblasts will be 1haracterized biochemically and compared to those expressed in leukemias induced by those viruses. The gag gene polyproteins synthesized by in vitro translation of 35S viral RNA isolated from virus infected fibroblasts and virus induced leukemias will be compared.