TRANSCRIPTIONAL REPRESSION BY P53 INVOLVES MOLECULAR-INTERACTIONS DISTINCT FROM THOSE WITH THE TATA BOX-BINDING PROTEIN

In addition to serving a role as a DNA binding-dependent transcription al activator, p53 has been reported to repress a variety of promoters that lack p53 binding sites, Data from recent studies have suggested t hat this activity is mediated via an interaction between p53 and the T ATA box binding protein (TBP), To investigate the functional relevance of this interaction in vivo, we have performed transient transfection assays in Drosophila Schneider cells, Wild-type p53 was found to repr ess expression from TATA box- but not initiator (Inr)-containing promo ters activated by GAL4-VP16, GAL4-ftzQ or Sp1, A mutant p53((His175)), defective in DNA binding and transcriptional activation, also inhibit ed TATA-dependent transcription activated by Sp1, However, p53 was una ble to repress a basal TATA promoter stimulated by overexpression of T BP, Furthermore, overexpression of TBP failed to rescue the p53-mediat ed repression of activated transcription and a p53 mutant with its N-t erminal TBP interaction domain intact, but defective in transcriptiona l activation and binding to TBP-associated factors (TAFs), was similar ly defective in transcriptional repression, These data suggest that a p53-TBP interaction is not sufficient for transcriptional repression b y p53 and that repression involves an interaction between p53 and othe r factors, such as TAFs, that are required for activated but not basal transcription, We suggest that p53-mediated repression results from s quelching of a factor limiting for activated transcription from TATA- but not Inr-containing promoters.