Influenza virus assembly and its defects.

The most abundant protein within the influenza virus particles is membrane protein (M protein) which forms an inner virus membrane under a lipid bilayer and plays the role of mediator during the process of assembly of a virus particle on plasma membranes. Ehrlich ascites tumor cells (EAT) when infected with influenza virus, strain WSN, produced virus-like particles containing greatly reduced amounts of M protein. Such particles were extremely fragile and easily lost hemagglutinins. The loss of this glycoprotein was accompanied by a decrease in infectious activity. SDS-PAGE analysis of RNA duplexes formed after hybridization of intracellular labeled mRNAs and unlabeled virion RNA showed that the mRNA for M protein was synthesized in EAT nearly in the same amounts as in productively infected chicken fibroblasts. Accordingly, M protein was readily revealed when the polypeptides of infected EAT were analyzed by SDS-PAGE. Thus, the reduced amount of M protein in virus particles was likely not due to the decrease in its synthesis but rather to its defective structure or to its defective transport and misintegration into plasma membranes of EAT.