Mechanism of Shope fibroma virus-induced suppression of host deoxyribonucleic acid synthesis.

The effects of treatment with live or inactivated Shope fibroma virus on host cell deoxyribonucleic acid (DNA) synthesis were determined. The incorporation of (3)H-thymidine into nuclear DNA was suppressed by both active and inactivated virus, although live virus was more effective. During the early phase of infection, stimulation of host nuclear DNA synthesis of up to 240% of control value was observed in cells infected with active virus. Inhibition of DNA synthesis began at about the 8th h and was maximal by 12 h postinfection. Virus inactivated by ultraviolet-irradiation or heat treatment did not induce viral DNA synthesis but was, nevertheless, able to suppress host DNA synthesis.