CYTOPLASMIC LOCALIZATION OF THE UNCOATING OF PICORNAVIRUSES

Early echovirus 12-cell interactions were studied by electron microscopy. Use was made of 2-thio-4-oxothiazolidine, rhodanine, a selective inhibitor of uncoating of the virus. Since the resolution of conventional ultrathin sections was too limited, combined autoradiography and electron microscopy was applied with the aid of highly purified [3H]leucine-labeled virus. In the presence of rhodanine, no accumulation of virions occurred on the surface of the cells; the radioactivity emanating from the virus was found randomly localized in the cytoplasm of infected cells, and no association with any particular cellular organell was detected. Quantitatively no difference was found in the number of grains per cell between rhodanine-treated or untreated cells. After reversal of the rhodanine block, uncoating (as measured by acquisition of light resistance of neutral red-sensitized virus in the cell) was very fast, requiring about 5 min. Under regular conditions of infection uncoating requires about 1-2 hr. Preincubation of the virus-cell complex at 22° accelerates subsequent uncoating at 37°. The data are compatible with the thesis that - at least in the presence of rhodanine - full infectious virus may reach the cell cytoplasm. © 1979.