The site of influenza virus-induced RNA synthesis in infected chick embryo cells has been determined by autoradiography. Following 5 min pulses of [H]-uridine, two distinguishable phases of induced RNA synthesis could be detected by grain counting in the nucleus, both of which occurred predominantly in the nucleoplasm. Cytoplasmic RNA synthesis could not be detected in fowl plague virus (FPV) infected cells; a significant increase in cytoplasmic grain count was detected in NDV-infected cells from 4 to 8 h after infection.

Cordycepin ('3-deoxyadenosine) inhibited nucleolar RNA synthesis in chicken embryo fibroblasts (CEF) to a greater extent than nucleoplasmic RNA synthesis; FPV-induced RNA synthesis in cordycepin-treated cells occurred in the nucleoplasm. α-amanitin treatment of FPV-infected cells inhibited the first peak of virus-induced nucleoplasmic RNA synthesis.

Fixed preparations of whole FPV-infected cells were incubated with an RNA-dependent RNA polymerase reaction mixture and examined by autoradiography. A peak of enzyme activity was detected at 3 h after infection in the nucleoplasm; a second peak of activity was detected at 6 h after infection and was wholly cytoplasmic.

We conclude that RNA synthesis in cells infected with influenza viruses occurs in the cell nucleus and that the increased level of nucleoplasmic RNA synthesis at approx. 1 h after infection signifies increased transcription of cell DNA. The evidence suggests that the microsomal RNA-dependent RNA polymerase found in FPV-infected cells does not function .


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