This proposal will investigate the molecular mechanisms involved in the abnormal growth regulation of murine lymphocytes transformed by the Abelson murine leukemia virus (A-MuLV). A detailed evaluation of the genetic and enzymatic properties of the A-MuLV transforming gene and its normal cellular homolog will be carried out. Preparation of improved serological and kinase substrate reagents will be done using synthetic peptide technology. Both wild type and mutants including partial or complete transformation defective strains, non-lethal variants, and temperature sensitive strains will be used to study the interaction of the viral phosphotyrosine kinase with the host cell environment. The temporal process and phenotypic progression of normal B lymphoid cells post-infection with A-MuLV towards the transformed state will be followed using newly developed cell culture techniques (Whitlock and Witte, 1982a). These studies will better define the nature of the A-MuLV target cell and cellular factors required for full expression of the transformed state in lymphoid cells.