Separation of cells containing R-type virus-like particles from a simian virus 40-induced hamster tumor cell line

Cells derived from a simian virus 40-induced hamster fibrosarcoma were separated into two distinct cell bands of differing buoyant densities. The lighter cell band or fraction (F1) had a buoyant density range of 1.025-1.032 g/ml and comprised 3.8% of the total cells applied to the gradient, whereas the heavier cell fraction (F2) had a buoyant density range of 1.054-1.074 g/ml and comprised 95.3% of the total cells applied. Both cell fractions were tumorigenic and did not differ greatly in cell type, viability, mitotic index, or their ability to incorporate [3H]thymidine. However, ultrastructurally, the F1 cells contained R-type virus-like particles within dilated intracisternal spaces and exhibited cytoplasmic vacuoles. In the F2 cells, few detectable R-type particles and cytoplasmic vacuoles were revealed by electron microscopy. The F2 cells demonstrated a twofold greater ability to incorporate [14C]protein hydrolysate into proteins than did the F1 cells.