Permanent expression of p53 in FR 3T3 rat cells but cell cycle‐dependent association with large‐T antigen in simian virus 40 transformants.

The p53 oncogene is thought to play a role in the proliferation of normal and transformed cells and its expression was postulated to be cell cycle dependent. Using flow cytofluorimetry sorting of populations of exponentially growing cells, coupled to a radioimmune assay, we have investigated the accumulation of p53 along the cell cycle in normal FR 3T3 rat cells as well as in two types of SV40‐transformed derivatives, one of which only expresses the large‐T protein during the G2 phase of the cell cycle. p53 was accumulated at a constant level throughout the cell cycle in FR 3T3 cells. Its level and stability increased to different extents in the two types of transformants. However, the formation of complexes between p53 and large‐T was modulated by the G2‐restricted accumulation of large‐T, thus leading to a differential increase in the levels of p53 both in exponentially growing cells and along the cell cycle. This increase in the levels of p53 appeared to be regulated at a post‐transcriptional level.