Proliferative activity and ribosomal RNA content of 3T3 and SV40-3T3 cells

The phenomenon of resistance of confluent 3T3 cells to serum stimulation of proliferation is investigated and shown to depend drastically on the kinetics of application of growth factors with the serum. The cellular content of ribosomal RNA is determined flow-cytometrically by measuring the red fluorescence of cells stained with acridine orange. Ribosomal RNA content of 3T3 cells, but not of SV40-3T3 cells, is shown to decrease after confluence. The kinetics of restoration of ribosomal RNA in stimulated 3T3 cells exhibits an increasing delay with increasing duration of quiescence. These and further results are consistent with "progression" to initiation of the cell cycle being closely associated with restoration of cellular content of ribosomes.