Identification of protein complexes containing the c-rel proto-oncogene product in avian hematopoietic cells

The c-rel proto-oncogene product has been identified as a 75 kDa protein expressed in lymphoid cells transformed by REV-T and Marek's disease virus. A 4.0 kb c-rel transcript is expressed in the bursa, spleen and thymus of chickens with highest levels of expression at 10 days post hatch. Using antiserum specific for the v-rel oncogene product, P75c-rel has been precipitated from [35S]methionine-labeled extracts of bursal, splenic and thymic lymphocytes. Additionally, proteins with the molecular mass of 40 kDa, 115 kDa, and 124 kDa co-immunoprecipitate. These proteins co-migrate with the proteins found associated with pp59v-rel in REV-T transformed lymphoid cells. Antiserum specific for pp40, the most abundant cellular protein associated with pp59v-rel, co-precipitates p75c-rel verifying the existence of p75c-rel/pp40 complexes in normal avian lymphocytes. Antiserum directed against the amino-terminal region of pp59v-rel fails to precipitate native p75c-rel complexes from normal lymphoid cells. In the presence of ionic detergents, antisera directed against the amino, middle and carboxy-regions precipitate equivalent amounts of p75v-rel. These results suggest that the amino-terminal region of p75c-rel is active in binding other proteins or is inaccessible to the antiserum due to the conformation of p75c-rel in the complex. Two p75c-rel complexes exist in the cytosol of normal lymphocytes. The most abundant complex contains 60% of the p75c-rel associated with p115 and p124. The remaining p75c-rel is associated with pp40.