RNA and protein synthesis in chick embryo lung cell monolayer cultures infected with influenza virus

Summary

When monolayer cultures of 15 day chick embryo lung cells were infected with PR8 strain influenza virus, newly-synthesised virus was first detected in the medium 4 hours post-infection, and continued to be released from the cells for at least 3 days. No obvious cytopathic changes were observed during this period. Synthesis of RNA and protein was measured in infected cells over a period of 13 hours post-infection by pulse-labelling with³H-uridine and¹⁴C-valine for 15 minutes following 30 minutes exposure to actinomycin D (1.5 μg/ml) at hourly intervals. The rate of incorporation of uridine into RNA of infected cells increased and decreased, relative to that in uninfected cells, three times during the 13 hour period, giving peaks of RNA synthesis in infected cells at intervals of approximately 4 hours. At its maximum rate, PR8 virus-induced RNA synthesis was less than 5% of total cellular RNA synthesis measured in the absence of actinomycin D. Labelled RNA extracted from actinomycin D-treated infected cells sedimented in the 16S–18S region on sucrose density gradients, and no such species of labelled RNA was found in uninfected cells. The rate of incorporation of valine into protein of infected cells varied by little more than 10% from that in uninfected cells during the period of study.

In a parallel series of experiments, 15 day chick embryo lung cells were infected with another strain of influenza A, fowl plague virus. Release of newlyformed virus occurred rapidly, from 4 to 12 hours post-infection, and was accompanied by extensive cytopathic effects. In contrast to PR8 virus infection, only a single peak of RNA synthesis was observed in fowl plague virus-infected cells, and thereafter there was a steady decline in the rates of both RNA and protein synthesis relative to uninfected cells.