Isolation and characterization of T antigen-negative revertants from a line of transformed rat cells containing one copy of the SV40 genome.

Negative selection with FUdR produced revertants from the transformed rat line 14B, which contains one insertion of the SV40 viral genome (Botchan, Topp and Sambrook, 1976). 14B contains nuclear T antigen, grows to a high density, grows in low serum and is anchorage-independent. The revertants fall into three classes with regard to viral DNA sequences: the SV40 DNA is retained; the SV40 DNA is retained but has undergone a deletion; and the SV40 DNA is lost, generating a cured cell. This heterogeneity is not a result of long-term passage. The revertants arise with a frequency of one in 8.4 X 10(5) cells after as few as 12 passages. All three classes of revertants are T antigen-negative, density-sensitive, more serum sensitive than 14B and anchorage-dependent. These data argue for a direct role of the functioning viral genome in the maintenance of the transformed state, and that with 14B, the phenotypes of transformation are not virus gene dosage-dependent.