Poliovirion-derived capsid proteins in subviral ribonucleoprotein complexes

Poliovirus containing [35S]methionine-labeled structural proteins was allowed to infect suspension cultures of HeLa cells. The experiments show that a small amount of virion-derived proteins (VDP) attached to the cells and that during infection at 37 degrees C but not at 15 degrees C, these proteins were associated with subviral particles containing RNA. By 3 hr postinfection 53% of the associated VDP was detected in components with low-sedimentation coefficients (below 150 S) and buoyant densities of 1.59, 1.54, and 1.40 g/cc. The rest of the labeled VDP was found mostly associated to a heavy subviral ribonucleoprotein (H-vRNP) compatible with a ribosome-RNA complex, due to its ssRNA content, its sedimentation behavior and buoyant density (1.54 g/cc), and its EDTA lability. VDP appeared in this H-vRNP early after infection (60 min) and accumulated as infection proceeded at expense of the low-sedimenting material. The accumulation of VDP in the heavy fraction (HF) paralleled polio-specific protein synthesis, and it was prevented by cycloheximide. These results suggest that a small amount of VDP remains associated with the infecting vRNA, and recommend a model which involves a subviral particle such as a functional molecule probably involved in the initial steps of poliovirus replication.