Evidence for free and metabolically stable p53 protein in nuclear subfractions of simian virus 40-transformed cells.

To determine functional subcellular loci of p53, a cellular protein associated with cellular transformation, we analyzed the nucleoplasmic, chromatin, and nuclear matrix fractions from normal mouse 3T3 cells, from methylcholanthren-transformed mouse (MethA) cells, and from various simian virus 40 (SV40)-transformed cells for the presence of p53. In 3T3 and MethA cells, p53 was present in all nuclear subfractions, suggesting an association of p53 with different structural components of the nucleus. In 3T3 cells, p53 was rapidly turned over, whereas in MethA cells, p53 was metabolically stable. In SV40-transformed cells, p53 complexed to large tumor antigen (large T) was found in the nucleoplasmic and nuclear matrix fractions, as described previously (M. Staufenbiel and W. Deppert, Cell 33:173-181, 1983). In addition, however, metabolically stable p53 not complexed to large T (free p53) was also found in the chromatin and nuclear matrix fractions of these cells. This free p53 did not arise by dissociation of large T-p53 complexes, suggesting that stabilization of p53 in SV40-transformed cells can also occur by means other than formation of a complex with large T.