Simian virus 40-transformed nonpermissive cells in which neither infectious viral DNA nor virions had previously been detected reproducibly yield low levels of infectious simian virus-40 DNA after treatment with extracts of normal permissive cells. Virions were obtained in one out of 37 experiments. Activation of the viral genome is detected only with normal permissive cell extracts and only in simian virus 40-transformed cell lines that are rescuable by heterokaryon formation or by treatment with chemicals. The activating factor(s) is insensitive to deoxyribonuclease and ribonuclease, but is sensitive to heat at 560 and to proteolytic enzymes.

An SV40-transformed BSC-1 cell line (BSC-SV CI I J ) , that had been cloned

PROPERTIES OF AN SV40-TRANSFORMED HAMSTER CELL LINE RESISTANT TO ACTINOMYCIN DThe biological properties of a hamster cell line C1 2 TSV-5/R derived from an SV40 turnour and made resistant to Actinomycin D ( 2 pg/ml) were investigated, in particular: turnorigenicity, in vitro growth on plastic or in soft agar, agar, persistence of SV40 specific neoantigens ( T and T S T A ) , and caryotype. When compared to the parental cell line (Cl 2 TSV-5), the tumorigenicity and the ability to grow in soft agar of the CI 2 TSV-5/R cells were strongly reduced (approximately 1,000 fold). Their growth on plastic was also clearly slowed. Although the