A Nuclear Labile Protein, p70, is Expressed Exclusively during G₀-S Transition but not in G₁ Phase of a Cell Cycle ts Mutant, tsJT16

抄録

tsJT16 is a cell cycle temperature-sensitive (ts) mutant from a Fischer rat cell line. When it is growth-stimulated from G₀ phase it enters S phase at the permissive temperature (34°C) but not at the nonpermissive temperature (40°C). It induces a nuclear labile protein, p70, when it is stimulated from G₀ phase at 34°C, but not at 40°C. In growing cell cycle it progresses through the S, G₂ and M phases at both temperatures but fails to pass through G₁ phase at 40°C. Here we described that p70 was synthesized neither in the randomly growing cycle nor in the G₁ phase synchronously progressing from M phase. The cells synchronized at early G₁ phase by culturing in serum-free medium for 7.5 h from G₁/S boundary induced c-fos and c-myc following serum addition, but under the same condition p70 was not synthesized. These results indicate that the synthesis of p70 is not required for progression of the G₁ phase of the growing cycle and can be used as an exclusive marker of G₀-S transition.