Equilibrium centrifugation of radiolabeled virus particles in the presence and absence of ST-246. Intracellular and extracellular virus particles were fractionated by equilibrium centrifugation on preformed cesium chloride gradients. (A) The radiolabeled viral DNA was measured by liquid scintillation counting. (B) The viral proteins in each fraction were detected by immunoblot analysis using antisera against L4 and B5 proteins. IMV, intracellular mature virus; CEV cell-associated enveloped virus; IEV, intracellular enveloped virus.