CHARACTERIZATION OF PHYSICAL INTERACTIONS OF THE PUTATIVE TRANSCRIPTIONAL ADAPTER, ADA2, WITH ACIDIC ACTIVATION DOMAINS AND TATA-BINDING PROTEIN

RNA polymerase II transcription requires functional interactions betwe en activator proteins bound to upstream DNA sites and general factors bound to the core promoter. Accessory transcription factors, such as a daptors and coactivators, have important, but still unclear, roles in the activation process. We tested physical interactions of the putativ e adaptor ADA2 with activation domains derived from acidic activator p roteins and with certain general transcription factors. ADA2 associate d with the herpesvirus VP16 and yeast GCN4 activation domains but not with the activation domain of yeast HAP4, which previously was shown t o be independent of ADA2 function in vivo and in vitro. Furthermore, t he amino terminus of ADA2 directly interacted with the VP16 activation domain, suggesting that ADA2 provides determinants for interaction be tween activation domains and the adaptor complex. Both TATA-binding pr otein (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 ge neral factors in yeast nuclear extracts, both factors interacted with VP16, but only the TBP/VP16 association was dependent on ADA2. In addi tion, ADA2 physically associated with TBP, but not with TFIIB. These r esults suggest that the role of ADA2 in transcriptional activation is to promote physical interaction between activation domains and TBP.