Relationship of endogenous murine xenotropic type C virus production to spontaneous transformation of cultured cells.

Spontaneous production of endogenous xenotropic viruses by clones of New Zealand Black (NZB) embryo cells occurs at a constant level even after several cell transfers. Foci of cell alteration occur spontaneously in some of the clonal lines after 6 to 10 passages. The amount of virus generated does not correlate with spontaneous transformation.. of these NZB cells nor of cells from NIH Swiss or BALB/c mice. The data demonstrate an intracellular regulation of xenotropic virus expression which remains stable over several cell generations and differs from that controlling cell transformation