Characterization of mouse mammary tumor viruses from primary tumor cell cultures. II. Biochemical and biophysical studies.

Primary mammary tumor cultures of RIII, GR, DD, BALB/c, and BALB/cfC3H mice were examined for mouse mammary tumor virus (MuMTV) production. Levels of production of 12-32 mug virus protein/day/75-cm2 culture flask could be maintained for 30-50 days with daily virus harvests. The viruses from tumor cell cultures of these mouse strains contained DNA polymerase with a strong preference for Mg++ over Mn++ as the divalent cation, a characteristic of DNA polymerase of MuMTV from mouse milk. These viruses from tumor cell cultures were excellent sources of MuMTV 3H-complementary DNA (complexed to 60-70S RNA) and radioactive 60-70S RNA, sufficiently free of contaminating murine leukemia virus nucleic acids, that can be used in molecular hybridization experiments. The effects of several culture parameters on MuMTV production were also studied.