[Intranuclear centers of influenza virus reproduction during the early stage of infection].

At 1--3 hours after infection of chick fibroblasts and a continuous dog kidney cell line MDCK with WSN and FPV viruses large virus specific structures were found containing parent nucleocapsids, newly synthesized virus-specific RNA and newly synthesized protein. The buoyant density of these structures in cesium chloride was 1.30--1.32 g/ml. The amount of newly synthesized RNA and protein in these structures increased linearly for 3 hours of infection. The parent and newly synthesized RNA in the structures were resistant to ribonuclease. When protein synthesis was inhibited by cycloheximide, parent nucleocapsids were also found in the large structures, and primary transcription of the viral genome occurred there as well. Some structures were destroyed upon sonication of the nuclei. It is suggested that in the observed structure the parent nucleocapsids are associated with cell components (possibly, nuclear chromatin), and centers of influenza virus reproduction arise in the sites of association.