EFFECT OF ACTINOMYCIN D ON SYNTHESIS OF INFLUENZA VIRUS-SPECIFIC RNA

The effect of actinomycin D on the replication of CAM strain of influenza A1 virus was studied in the human conjunctival cell line, clone 1-5C-4. Actinomycin D in a concentration of 0.5 mcg/ml suppressed the virus yield to less than l/1000th of that from the uninhibited culture. When the addition of actinomycin D was delayed, the resistance of the production of virus and viral components to actinomycin D developed progressively in the order of the soluble antigen, hemagglutinin, and the infective virus. The synthesis of virus-specific RNA was demonstrable by the incorporation of tritiated uridine when actinomycin D was added to the culture at 6 hours after infection, but not when it was added at 1 hour after infection. These findings indicated that actinomycin D illhibits influenza virus replication because it inhibits the synthesis of virusspecific RNA and that, however, it does not directly block virus-specific RNA synthesis per se but exerts the inhibitory effect on some event(s) preceding virus-specific RNA synthesis. In FL cells, in which CAM virus undergoes an abortive multiplication cycle, virus-specific RNA was synthesized in the same period after infection and in a similar quantity as in clone 1-5C-4 cells in which complete multiplication occurs. © 1969 Springer-Verlag.