RNA polymerase II transcription requires functional interactions between activator proteins bound to upstream DNA sites and general factors bound to the core promoter. Accessory transcription factors, such as adaptors and coactivators, have important, but still unclear, roles in the activation process. We tested physical interactions of the putative adaptor ADA2 with activation domains derived from acidic activator proteins and with certain general transcription factors. ADA2 associated with the herpesvirus VP16 and yeast GCN4 activation domains but not with the activation domain of yeast HAP4, which previously was shown to be independent of ADA2 function in vivo and in vitro. Furthermore, the amino terminus of ADA2 directly interacted with the VP16 activation domain, suggesting that ADA2 provides determinants for interaction between activation domains and the adaptor complex. Both TATA-binding protein (TBP) and TFIIB have previously been shown to interact directly with the VP16 activation domain in vitro (Stringer, K. F., Ingles, C. J., and Greenblatt, J. (1990) Nature 345, 783-786; Lin, Y. S., Ha, I., Maldonado, E., Reinberg, D., and Green, M. R. (1991) Nature 353, 569-571). Interestingly, when binding was tested between VP16 and these general factors in yeast nuclear extracts, both factors interacted with VP16, but only the TBP/VP16 association was dependent on ADA2. In addition, ADA2 physically associated with TBP, but not with TFIIB. These results suggest that the role of ADA2 in transcriptional activation is to promote physical interaction between activation domains and TBP.

The ability of p53 to function as a tumor suppressor is linked to its function as a transcriptional activator, since p53 mutants that do not transactivate are unable to suppress tumor cell growth. Previous studies identi®ed an activation domain in the amino terminal 40 residues of the protein, a region that binds to several general transcription factors and to some oncogene products. For example, mdm-2, a cellular oncoprotein, binds to this region and represses p53 transactivation. Here we describe a new activation domain within the amino terminus of p53 that maps between amino acids 40 ± 83, and whose residues trp-53 and phe-54 are critical for function both in yeast and in mammalian cells. In vivo studies in yeast show that the new activation subdomain, unlike the previously described, is mdm-2 independent. Both p53 activation subdomains (1 ± 40 and 40 ± 83) require the yeast adaptor complex ADA2/ADA3/GCN5 for transcriptional activation. Moreover, since activation by p53 requires GCN5's enzymatic histone acetyltransferase domain, p53 may regulate gene expression by in¯uencing chromatin modi®cation.Keywords: adaptor; genetics; mdm-2; p53; transcription IntroductionThe tumor suppressor protein p53 (for a review, see Donehower and Bradley, 1993;Ko and Prives, 1996;Levine, 1993 and references therein) is inactivated in more than half of all human tumors . p53 is a sequence-speci®c transcription factor that suppresses oncogenic transformation (Eliyahu et al., 1989;Finlay et al., 1989) and induces cell cycle arrest (Leonardo et al., 1994) or programmed cell death (Clarke et al., 1993; Lowe et al., 1993a,b) in response to DNA damage.Three distinct domains have been identi®ed within p53: the acidic aminoterminus is an activation domain (Fields and Jang, 1990;Funk et al., 1992;Raycroft et al, 1990), the hydrophobic central region contains a sequence-speci®c DNA-binding domain (Bargonetti et al., 1993;Wang et al., 1993), and the basic carboxyterminus comprises an oligomerization domain (Clore et al., 1994;Jerey et al., 1995;Lee et al., 1994;Sakamoto et al., 1994;Sturzbecher et al., 1992) and a region that regulates DNA binding anity Hupp et al., 1992;Waterman et al., 1995). Hot-spots for p53 mutations in tumors (Hollstein et al., 1991;Levine et al., 1991) are found predominantly in the central DNA-binding domain.In addition, p53 can act as a transcriptional repressor, to down-regulate promoters lacking wild type p53 binding sites (Ginsberg et al., 1991;Santhanam et al., 1991;Subler et al., 1992). The amino terminal transactivation domain of p53 also is required for its inhibitory eects on transcription (Sang et al., 1994;Subler et al., 1994).Tumor suppression and transcriptional activation are strongly correlated functions of p53 (Farmer et al., 1992;Fields and Jang, 1990;Funk et al., 1992). Mutations or deletions in the aminoterminus of p53 coordinately abolish transactivation and tumor suppressor functions. Tumor-derived p53 mutants fail to activate transcription of wild type p53 responsive genes. Furthermore, mdm-2,...