TRANSCRIPTIONAL REPRESSION BY THE C-TERMINAL DOMAIN OF P53

We have previously shown that monomeric p53 can transactivate target g enes in vivo and that C-terminal fragments of p53 are oncogenic. To fu rther elaborate these findings a series of C-terminal truncations of p 53 was generated. The transactivation capacity and the ability of the truncated p53 to suppress oncogene-mediated transformation were studie d. We found that p53 truncated at amino acid 303 (p53wtdl303) can stil l function in both assays, though less efficiently than full length wi ld type (wt) p53. Transforming C-terminal fragments inhibited transact ivation induced by full length wt p53. Surprisingly, they also inhibit ed transactivation by wtdl303, with which they do not share e any over lapping sequences. Furthermore, the C-terminal fragments repressed the transactivation domains of several viral and cellular transcriptional activators. These data raise the possibility that the C-terminal doma in of p53 may compete with the p53 transactivation domain for a common basal transcription factor.