FIG. 4.
Analysis of cell-associated and released virions by CsCl centrifugation. RK13 cells were infected with WR.c1 (▪), WR.c3 (▴), or vaccinia virus strain WR (•) and labeled with a mixture of [35S]methionine and [35S]cysteine. Virus particles associated with the cells (A) and in the culture medium (B) were concentrated by sedimentation through a sucrose cushion, applied to CsCl gradients, and centrifuged. Fractions were collected from the bottom of the tube, and radioactivity was determined by scintillation counting.