Studies on polysomes synthesizing influenza virus haemagglutinin

A fraction of polysomes synthesizing fowl plague virus (FPV) haemagglutinin (HA) was isolated from an infected chick embryo fibroblast (CEF) culture using a double immunoprecipitation assay. In an immunoprecipitate of HA-synthesizing polysomes (HA precipitate) the content of the HA polypeptide was increased with respect to the M1 + NS1 polypeptides as compared to a preparation of unprecipitated polysomes. In the HA precipitate, besides mRNA coding for HA synthesis, we have detected mRNAs corresponding to genes 1, 2 and 3 coding for high molecular weight P proteins. Studies of a cytoplasmic extract (CE) from FPV-infected CEF cultures in a sucrose density gradient revealed a fraction of polysomes with a sedimentation value of about 500S; the composition of virus-specific polypeptides and mRNA of the fraction was similar to that of the HA precipitate. It is thought that P proteins are synthesized on membrane-bound polysomes located closely to HA-synthesizing polysomes.