REGULATORY MECHANISM OF SIMIAN VIRUS-40 GENE-EXPRESSION IN PERMISSIVE AND IN NONPERMISSIVE CELLS

Primary or continuuos lines of mouse cells (3T3) are nonpermissive for simian virus 40 (SV40). Abortively infected cells synthesize tumor antigen (T antigen) but not viral DNA and virus capsid protein (V antigen). V antigen was obtained when SV40 DNA was injected into 3T3 cells. This late gene expression induced by SV40 DNA is gene dose dependent. Early SV40 gene expression also appears to be correlated with the quantity of injected DNA molecules per 3T3 cell. T antigen formation can be detected after microinjection of only 1-2 DNA molecules, but the intensity of intranuclear T antigen fluorescence is significantly brighter with injection of higher concentrations of viral DNA. In permissive cells (TC7), early and late SV40 gene expression is not related to the number of injected molecules. Microinjection of 1 DNA molecule induced T and V antigen formation with the same efficiency as microinjection of 2000-4000 molecules. The question of whether late SV40 gene expression is directly related to the quantity of an early virus-specific product was approached by microinjection of early SV40 complementary RNA together with small amounts of viral DNA. V antigen was obtained in a high proportion of recipient 3T3 cels at conditions where microinjection of viral DNA alone induced T but not V antigen synthesis.