The Prevention of Early Vaccinia-virus-induced Cytopathic Effects by Inhibition of Protein Synthesis

strain of vaccinia vh'us caused rounding of all cells within 2 to 3 hr after infection. Puromycin, at a concentration of 330 #g./ml., completely pre-vented the early virus-induced cytopathological changes as well as virus multiplication; however, at 33 #g./ml. the compound id not prevent he cytopathic effects of vaccinia virus, in spite of the fact that virus multiplica-tion was largely inhibited. Treatment of cells for 4 hr with puromycin at 33o/zg./ml. did not alter the rate of cell division when the compound was removed. When the antibiotic (33o/zg./ml.) was removed from infected cultures after a treatment period of 4 hr, virus-induced cell damage began al-most immediately after removal and by I hr all cells were rounded. Actinomycin D, 5/zg./ml., also protected the cells from the early vaccinia-virus-induced cytopathic effects. At o'5/*g./ml., although growth of virus was inhibited, no protection against viral cytopathic effects was observed. In LLC-MK x cells virus-induced morphological damage was not pre-vented by p-fluorophenylalanine, 5-fluoro-e'-deoxyuridine, and isatin-fi-thiosemicarbazone--compounds k own to inhibit the reproduction of vaccinia virus. Ultraviolet-irradiated virus, which had lost its infectivity, was still capable of causing early cell damage. These findings uggest that he early virus-induced cytopathological effects, previously considered the ' toxic ' effects of the virus, are brought about by the synthesis of virus-induced protein(s)