WILD-TYPE BUT NOT MUTANT-P53 CAN REPRESS TRANSCRIPTION INITIATION INVITRO BY INTERFERING WITH THE BINDING OF BASAL TRANSCRIPTION FACTORS TOTHE TATA MOTIF

It has previously been shown that excess wild type (wt) p53 can repres s the transcriptional activity of a variety of promoters in intact cel ls. To determine whether this transcriptional repression represented a direct effect of p53, wt and mutant p53 were prepared from E. coli-pr oduced p53 and from insect cells infected with a recombinant baculovir us. 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 specif ically the formation of the transcription preinitiation complex becaus e preformed initiation complexes were completely refractory to wt p53, as was also the process of transcript elongation. Wild-type but not m utant p53 interfered with the stable binding of TBP and TFIIA to the T ATA motif, although both wt and mutant p53 could associate in vitro wi th purified TBP. We propose that upon binding to TBP, wt but not mutan t 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 pro liferation and to interfere with neoplastic processes.