Compartmentalization of subviral particles during poliovirus eclipse in HeLa cells

HeLa cells were preincubated with radiolabelled poliovirus type 1 at 26 degrees C, such that the 160S virions were internalized, but not altered structurally. The temperature was then shifted to 37 degrees C to study the intracellular redistribution of the virions and the modifications they undergo at that temperature. Using subcellular fractionation in isoosmotic Nycodenz gradients, we obtained evidence for the rapid loss of virions from the plasma membrane and from a vesicular fraction, as well as for the formation of two populations of intracellular 135S particles. The first population was associated with lysosomes and was slowly converted to (RNA-containing) 110S particles. In the presence of the lysosomotropic agent chloroquine, the lysosomal 135S population was converted to 80S empty capsids. The second 135S population, which was not associated with any organelle, was converted to 80S empty capsids. Similar observations were made during unsynchronized infection at 37 degrees C. We propose a model for infection in which 135S particles cross a membrane barrier, and are uncoated in the cytosol.