Avian reticuloendotheliosis virus (REV-T) is the most virulent of all retroviruses. The oncogene of REV-T, v-rel, transforms and prevents the subsequent differentiation of lymphoid cells at different stages of B cell development. REV-T converts normal cells to a tumorigenic state providing an excellent model for studies on oncogenic mechanisms. The v-rel oncogene is distinct from other known oncogenes and encodes a 59 kDa protein which is associated with a distinct set of cellular proteins. There are two pp59v-rel cytosolic complexes which contain the product of the c-rel proto-oncogene (p75c-rel) and the constitutive form of heat shock protein 70 (p70hsc). The major cytosolic complex is distinct in that it contains a 40 kDa phosphoprotein (pp40). Twenty percent of pp59v-rel in the cytosol is not associated with pp40 but with two high molecular weight proteins (p115, p124). Purified pp59v-rel cytosolic complexes contain an associated serine kinase activity. Approximately ten percent of the pp59v-rel is present in nuclear complexes which contains pp40. In normal avian lymphoid cells p75c-rel is complexed with proteins of the same apparent molecular mass as those associated with pp59v- rel in REV-T transformed cells. The major p75c-rel complex contains p115 and p124. The less abundant complex contains p75c- rel associated with pp40. The c-rel proto-oncogene and v-rel proteins activate transcription in yeast and the region responsible for activation is also necessary for oncogenic transformation by v-rel. However, in normal and transformed avian lymphoid cells p75c-rel is a cytosolic protein. It is likely p75c-rel is a transactivating factor which is sequestered in the cytosol of unstimulated lymphoid cells. When REV-T transformed cells are exposed to heavy metals, p75c-rel levels increase and nuclear translocation occurs. The objectives of this proposal are to 1) perform mutational analysis on v-rel to correlate transforming ability with the binding of cellular proteins to the v-rel protein; 2) determine whether any of these proteins associated with p75c-rel are involved in nuclear translocation; 3) molecularly clone and sequence the gene encoding pp40 and define its tissue specific expression; 4) prepare monoclonal antibodies against the cellular proteins associated with pp59v-rel and p75c-rel.