Virus fractionation. Purified virion preparations (V) were separated into capsid (C) and envelope (E) fractions and analyzed by immunoblotting with sera against the major capsid protein UL19, the portal protein UL6, the capsid component UL17, envelope glycoprotein H (gH), or the UL37 tegument protein, as well as with the UL25-specific serum. Molecular mass markers are indicated on the left.