Nucleic acid synthesis in HeLa cells infected with Shope fibroma virus

Infection of HeLa cell monolayers with Shope fibroma virus (SFV) is accompanied by the synthesis in the cytoplasm of a new RNA. Sucrose density gradient profiles reveal a heterogeneous, rapidly labeled RNA sedimenting around 16 S, shifting toward higher S values as time after infection increases. RNA synthesis is first noted 6 hours after infection, reaches a peak at 12 hours, and can still be detected at 25 hours after infection. The labeled RNA is associated with polyribosomes.The incorporation of thymidine-³H into acid-precipitable material in the cytoplasm of infected cells undergoes marked stimulation at 6 hours after infection, is maximal at 8 hours, and has ceased at 14 hours after infection. This indicates that progeny viral DNA synthesis occurs during the early phases of RNA synthesis.The new virus-induced activity in the cytoplasm is accompanied by a suppression of host genome function. The synthesis of RNA in the nucleus is decreased by 40% at 10 hours after infection. The incorporation of uridine-¹⁴C into ribosomal RNA in the cytoplasm is even more severely depressed.