Association of influenza virus proteins with cytoplasmic fractions

Abstract

Cytoplasmic extracts of chick embryo fibroblasts infected with fowl plague virus were separated into fractions containing smooth membranes, rough membranes, free ribosomes and polysomes, and a soluble fraction. Viral proteins were analyzed in these fractions by polyacrylamide gel electrophoresis. The hemagglutinin glycoproteins were found to be associated with rough and smooth membranes, and pulse-chase experiments revealed that the large glycoprotein HA migrates from rough to smooth membranes where it is cleaved into glycoproteins HA 1 and HA. The nonglycosylated envelope polypeptide M was located predominantly in smooth membranes, the nucleocapsid protein NP in a fraction of intermediate density, and the nonstructural polypeptide NS in the fractions containing ribosomes. A large amount of protein P was found in the soluble fraction. If glycoprotein synthesis was inhibited by glucosamine or deoxyglucose the predominant virus-specific component located on smooth membranes was protein HA 0 thought to be the unglycosylated or incompletely glycosylated polypeptide of glycoprotein HA. Like HA, HA 0 migrated from rough to smooth membranes where it was also cleaved into two fragments. These data show that polypeptide HA 0 has a high affinity for membranes and they further underline the close relationship between proteins HA and HA 0.