Infective substructures of Sendai virus from infected Ehrlich ascites tumor cells

Replication of Sendai virus. II. Steps in virus assembly

Chick embryo fibroblast cultures infected with Sendai virus were incubated with (3)H-uridine in the presence of actinomycin D beginning at 18 hr after infection. The 35 and 18S virus-specific ribonucleic acid (RNA) components were found in a ribonuclease-sensitive form in the cell and appeared to be associated with polyribosomes. Newly synthesized 57S viral RNA was rapidly coated with protein to form intracellular viral nucleocapsid, and no 57S RNA was found "free" (ribonucleasesensitive) in the 2,000 x g supernatant fraction of disrupted cells. The nucleocapsid from detergent-disrupted Sendai virus and that from disrupted cells were indistinguishable in ultrastructure and buoyant density, and neither was found to be infectious or have hemagglutinating activity. Kinetic studies of nucleocapsid and virus formation indicated a relative block in conversion of viral nucleocapsid to complete enveloped virus in these cells, resulting in accumulation of large amounts of nucleocapsid in the cell cytoplasm.

Fate of Sendai virus ribonucleoprotein in virus-infected cells

The cytoplasmic extracts of Ehrlich ascites tumor cells infected with (32)PO(4) and (3)H-leucine-labeled Sendai virus have been examined during the course of infection with respect to sedimentation behavior and buoyant densities of input virus radioactivity. It was found that (32)P and (3)H radioactivities were coincident, and, at 30 min after infection, the bulk of radioactivity was recovered in the polysome region of a sucrose gradient in the position of Sendai virus ribonucleoprotein (210S). The heterogeneity of radioactivity profiles appeared at 1 hr after infection and increased during 6 hr of incubation. The buoyant densities of input virus components were determined by banding in CsCl gradient. Here again the bulk of coincident (32)P and (3)H radioactivity at 30 min after infection banded at the same density as Sendai virus ribonucleoprotein (1.31 g/cm(3).) This component disappeared at 3 hr after infection, and (32)P and (3)H radioactivities were now found in components banded at densities 1.38, 1.41, 1.45, 1.49, and 1.55 g/cm(3). The results presented are consistent with the idea that virus ribonucleoprotein is retained in the cytoplasm of infected cells during at least 6 hr of incubation, being partly deproteinized in the course of infection. The nature of components which banded at rho = 1.41, 1.45, 1.49, and 1.55 as complexes of partly deproteinized ribonucleoprotein with ribosomes will be described in a separate paper.