Effect of temperature and cell density on cellular protein content in temperature-sensitive mutants of rat 3Y1 diploid fibroblasts.

We examined cellular protein content in four temperature-sensitive (ts) mutants of rat 3Y1 fibroblasts (3Y1tsD123, 3Y1tsF121, 3Y1tsG125, and 3Y1tsH203) under various conditions of culture that affect cell proliferation. When proliferation of the ts mutants was inhibited at a nonpermissive temperature (39.8 degrees C) in the G1 phase, prominent accumulation of cellular protein occurred in three mutants (3Y1tsF121, 3Y1tsG125, and 3Y1tsH203) but not in 3Y1tsD123. The over-accumulation of protein at 39.8 degrees C in the former three mutants was inhibited at high cell densities. At low cell densities there was an upper limit in the protein accumulation at 39.8 degrees C. When the three mutants, proliferation-arrested at high cell densities at 33.8 degrees C, were replated sparsely in fresh medium and shifted to 39.8 degrees C, proliferation was completely inhibited, whereas over-accumulation of protein occurred. These results indicating dissociation of protein accumulation and cell proliferation suggest that the two events are regulated by different mechanisms.