Wild-type but not mutant p53 can repress transcription initiation in vitro by interfering with the binding of basal transcription factors to the TATA motif.

It has previously been shown that excess wild type (wt) p53 can repress the transcriptional activity of a variety of promoters in intact cells. To determine whether this transcriptional repression represented a direct effect of p53, wt and mutant p53 were prepared from E. coli-produced p53 and from insect cells infected with a recombinant baculovirus. When added into an in vitro transcription system, wt p53, but not mutant p53 reduced markedly transcription from the c-myc promoter, as well as from an array of other promoters, with the exception of an MHC class I gene promoter. The presence of wt p53 seemed to affect specifically the formation of the transcription preinitiation complex because preformed initiation complexes were completely refractory to wt p53, as was also the process of transcript elongation. Wild-type but not mutant p53 interfered with the stable binding of TBP and TFIIA to the TATA motif, although both wt and mutant p53 could associate in vitro with purified TBP. We propose that upon binding to TBP, wt but not mutant p53 specifically blocks the ability of TBP to engage in interactions required for efficient transcriptional initiation. This may account, at least in part, for the ability of excess wt p53 to inhibit cell proliferation and to interfere with neoplastic processes.