p53 is associated with a 35 kD protein in cells transformed by simian virus 40.
The p53 protein is functionally implicated in the normal control of cell proliferation and, abnormally, in cell transformation. p53 is believed to function via specific cellular target proteins and activated mutants of p53 are associated with proteins of the hsp/hsc 70 heat shock family. However, cellular target proteins of wild type p53 have not, as yet, been described. With the aim of detecting such targets we have screened for cellular protein(s) that co-precipitate with wt p53. We now describe a 35 kD protein co-precipitated with p53 from SV40-transformed cells (a similar protein is detectable in non-viral transformed cells). The 35 kD protein does not appear to be a degradation product of p53. In sequential immunoprecipitations the 35 kD protein was depleted in parallel with p53, with which it appeared to be physically associated. This was substantiated by dissociation experiments in which the 35 kD protein was dissociated under conditions that also dissociate p53 from SV40 large T antigen. Thus wt p53 appears to interact with a cellular protein of 35 kD, the identity of which is under investigation.