Control of influenza virus polypeptide synthesis

Influenza A (fowl plague) virus polypeptide synthesis in infected chick embryo fibroblasts occurs in an early (up to 2.5 hr pi) and a late stage. RNA extracted from infected cells at early and late times after infection directed the synthesis in vitro of virus polypeptides in similar proportions to those made in vivo at the corresponding times, suggesting that this temporal control operates at the level of virus mRNA synthesis. However, the pattern of polypeptides synthesised in vitro and in vivo in response to RNA formed during infection in the presence of the protein synthesis inhibitor cycloheximide indicated that the predominant synthesis of certain virus mRNAs up to 2.5 hr pi was not due to selective transcription of the infecting virus genome by the virion polymerase. It is suggested that virus-specific transcription occurs in three stages: first, unselective transcription of all the virus genes by the virion polymerase; second, amplification of synthesis of the mRNAs encoding the early polypeptides; and third, amplification of late mRNA synthesis. The transition between each of these stages appears to be dependent on the synthesis of new and presumably virus-specified polypeptides.