Fluorescence spectrophotometric study of structural alterations in the capsid of poliovirus

Concerted structural alterations of viral proteins in the capsid of poliovirions are induced after adsorption to specific receptors on the host cells. Similar changes occur in vitro during exposure to low and high pH, elevated temperature or to denaturing agents. These structural alterations can be monitored conveniently by recording changes in the intrinsic fluorescence of the poliovirus-capsid and by following the fluorescence intensity after addition of ethidium bromide to virus particles. Application of these fluorescence techniques reveals that the uncoating of the virions in vitro occurs in two distinct steps: 1. entry of ions, e.g. ethidium bromide, 2. development of sensitivity of the virion RNA to RNase and release of the RNA. We confirm different structural stabilities of the virions at several pH values to elevated temperatures and a stabilizing effect of arildone on poliovirions.