Continued characterization of RadLV/VL3 structural proteins purified with the aid of monoclonal hybridoma antibodies and studied by SDS-PAGE, by cross-reactivity with antibodies to the corresponding proteins of other murine types C viruses, and by tryptic digestion and high-pressure liquid chromatography of the hydrolysate peptides. Production of monoclonal antibodies against the putative transforming gene products of radiation- and virus-induced murine thymic lymphomas, using immunization with lymphomas from mice congenic to C57BL/Ka but differing at the H-2 locus, followed by challenge with the syngeneic radiation-induced non-producer lymphoma cell line, BL/Bl12-NP. Spleen cells from immunized mice will be fused with HAT-sensitive mouse myeloma cells and the resultant hybridomas screened for specific antibody production by binding to BL/RL12-NP cells in ELISA or indirect IF assays. If specific monoclonal antibodies are obtained, they will be coupled to columns to isolate the relevant antigen by affinity chromatography, and will be used to immunoprecipitate the translation products of candidate mRNA's that have been identified in the non-producer cells. Further studies of the thymic target cell population for neoplastic transformation, and of the biological significance of the recently described tymic "nurse cells" in their maturation. Studies of the relevance of virus-impaired immunocompetence in leukemogenesis. Studies of the evolution of autonomy in autochthonous lymphomas.