Viral infection across species barriers: reversible alteration of murine sarcoma virus for growth in cat cells

Infection of cat embryo cells by a centrifugally induced aggregate of murine sarcoma virus and feline leukemia virus gave rise to a defective, focus-forming virus which propagated in cat cells, but not in mouse cells. This virus, apparently enveloped with a feline leukemia virus coat, was later subjected to aggregation with murine leukemia virus, whereupon it regained the capacity for growth in mouse cells.