Analysis of the inhibitory effect of canavanine on the replication of influenza RI/5+ virus. I. Inhibition of assembly of RNP.

Abstract When influenza A 2 /RI/5 + virus-infected 1-5C-4 cells were incubated in medium containing 2 μg/ml of canavanine (an arginine analog) from 4 hr after infection, virus growth was completely inhibited. The mechanisms of inhibition by canavanine were investigated by immunofluorescent staining or isotope labeling of cells. The results indicated that in canavanine-treated cells all known viral proteins were synthesized, but most of the nucleocapsid protein (NP) and nonstructural protein (NS) was present in the nucleus, in contrast to control cells in which they were distributed throughout the whole cells. Further, formation of viral ribonucleoprotein (RNP) was inhibited and most NP was present in a nonassembled, soluble form. This action of canavanine was reversible. When arginine was added to canavanine-treated cells, viral RNP soon became detectable in the cytoplasm, and this was followed by the production of infectious virus. However, simultaneous addition of cycloheximide with arginine did not restore the formation of RNP or virus production. Based upon these findings, it is suggested that the inhibitory effect of canavanine on the replication of influenza A 2 /RI/5 + virus is inhibition of assembly of viral RNP.