ROLES OF THE SIMIAN VIRUS-40 TUMOR-ANTIGENS IN TRANSFORMATION OF CHINESE-HAMSTER LUNG-CELLS

SV-40 mutants with deletions between 0.54-0.59 map units direct the synthesis of defective 20K [kilodalton] t antigens. These deletion mutants transformed actively growing CHL cells nearly as efficiently as did wild-type virus, in the focus formation assay or the growth in soft agar assay. When CHL cells were in a resting state during infection, the transformation frequency of the mutants relative to wild-type dropped approximately 50-fold. The presence of the phorbol ester, TPA [12-O-tetradecanoyl-phorbol-13-acetate], diminished this difference. CHL cell lines transformed by the deletion mutants and selected by the focus assay grew almost as efficiently in soft agar as lines transformed by wild-type SV-40. Both produced tumors in nude mice. The function of the 20K t antigen was discussed.