Type-specific determinants on proteins of an endogenous C3H mouse mammary tumor virus (MMTV) distinguish this virus from highly oncogenic exogenous MMTVs

The genetically transmitted endogenous MMTV isolated from C3H mice after removal of the milk-transmitted virus by foster nursing is designated C3Hf MMTV to distinguish it from the highly oncogenic milk-transmitted exogenous virus designated C3H MMTV. We have isolated a MMTV-expressing C3Hf mammary tumor cell line which has no exogenous proviral sequences detectable by analysis of DNA fragments generated by Pst I restriction endonuclease. This cell line produced sufficient C3Hf MMTV to allow purification of the major proteins and an antigenic comparison of this virus with highly oncogenic exogenous MMTVs from C3H, GR, and RIII strains of mice. The envelope glycoproteins, gp52 and gp36, purified from the C3Hf MMTV, were found to have both group- and type-specific reactivities. Only C3H MMTV gave incomplete competition in the gp36 assay and, therefore, could be distinguished from C3Hf, RIII, and GR MMTVs which gave complete competition. Unique antigenic determinants exist on the gp52 of C3Hf MMTV since it is the only virus to give complete competition in the gp52 radioimmunoassay. GR MMTV competed only 60%, whereas C3H and RIII MMTVs gave 80% competition. This was the first demonstration that RIII and C3Hf MMTVs were immunologically distinct. Only group-specific reactivity was found with the gag-coded MMTV p27; however, group and class antigenic determinants were found on the gag-coded MMTV p10.