Purification of HHV-6A. A and B. Material in pooled iodixanol gradient fractions were concentrated by centrifugation, separated by 6–15% SDS-PAGE and visualized by silver nitrate staining or western blot using the viral specific (gp60/110) antibody. C. DNA analyses of iodixanol gradient fractions. The number of viral DNA copies in iodixanol gradient fractions of two independent experiments was measured by TaqMan based real-time PCR and the densities of the fractions by refractometer. D. The proteins in gradient purified material of HHV-6A- and mock-infected cultures were compared by SDS-PAGE stained with silver nitrate. Fresh culture medium was analyzed as a control. Estimated molecular weights in kD of the detected proteins are indicated. All samples in each separate analysis were equalized to each other based on sample volume. H, M and Mw indicate HHV-6A, mock and molecular weight marker.