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Evidence accumulated in the last 3 years indicates that cells experimentally transformed to malignancy by DNA viruses retain noninfectious viral genes that are continuously transmitted in subsequent generations with at least some manifestations that are reminiscent of bacterial lysogeny.' Perhaps the most interesting manifestation of these noninfectious viral genes is the synthesis of specific tumor antigens that are not components of the virus particle (virion) but are identical with antigenic materials synthesized early after a cytocidal infection of normal cells. Of special interest in connection with these tumor antigens in animal cells are the previous demonstrations that new antigens appear within a few minutes after viral infection of bacteria prior to the onset of DNA synthesis and that new traits acquired by lysogenic bacteria can also be demonstrated early after lytic infection of bacteria.2 The demonstration that inhibitors of DNA synthesis, which can prevent the production of virion antigens in mammalian cells infected by the oncogenic SV403 and adenoviruses,j 5 do not prevent the synthesis of the specific tumor antigens, indicated that production of the tumor antigens was not dependent on replication of new viral DNA. However, formation of the tumor antigens was not prevented by such inhibitors of protein synthesis as p-fluorophenylalanine (500 ,ug/ml) and puromycin (10 Ag/ml the maximum concentration that could be used without destroying the primary African green monkey kidney cells).' The data reported on the effect of actinomycin D (dactinomycin) at 1 ,ug/ml for a period of 48 hr after addition of the virus show that the amount of tumor antigen formed was diminished but not suppressed; this observation was interpreted as indicating that synthesis of the tumor antigens requires DNA-dependent RNA.6 Since this amount of dactinomycin was said to be so toxic for the cells that observations for more than 24-48 hr were not possible,6 and since it was not shown that the effect of this drug was reversible before death of the cells, it is difficult to evaluate the significance of the observed depression in the amount of tumor antigen formed. The demonstrated capacity of chloramphenicol (at 25 ,ug/ml) to stop with 1 min or less those reproductive processes of phages T2 and T4 that depend on protein synthesis,7 prompted the investigation of the eff ect of this drug on the synthesis of the tumor and virion antigens in cells infected with the SV40 virus, particularly since recent studies indicated that under certain conditions this drug can inhibit protein synthesis in mammalian cells as well as in bacteria.8-10 The investigation ,of the effect of streptovitacin A-an hydroxylated analogue of cycloheximide (actidione)-was prompted by several factors: (1) despite its lack of antibacterial activity it has been shown to be capable of stopping protein synthesis in mammalian cells within 15-30 min with a depression of DNA synthesis that does not exceed 50 per cent and with no depression of RNA synthesis; (2) the suppression of protein synthesis is completely reversible within a short time after removal of the

Different effects of chloramphenicol, dactinomycin, and streptovitacin A on synthesis of tumor and virion antigens in SV40 virus-infected cells.