Murine xenotropic type C viruses. III. Phenotypic mixing with avian leukosis and sarcoma viruses.

Phenotypic mixing has been demonstrated between murine and avian type C viruses. Pseudotypes of Rous sarcoma virus (RSV) have been obtained which carry envelope determinants derived from xenotropic or ecotropic murine leukemia viruses (MuLV). Mouse sarcoma virus (MSV) pseudotypes have been constructed with envelope characteristics of subgroup C and E avian leukosis viruses. RSV pseudotypes produced with MuLV can infect mammalian cells, and MSV pseudotypes with avian leukosis virus infect chicken cells. The expression of transformation by these sarcoma genomes seems suppressed in certain of the heterologous hosts. Exogenous infection of mammalian cells by RSV(MuLV) results in not only transformation of the heterologous host but also the production of infectious progeny virus. The extent of this virus production appears determined by the ability of the helper virus to replicate in the host cell.