YEAST ADA2 PROTEIN BINDS TO THE VP16 PROTEIN-ACTIVATION DOMAIN AND ACTIVATES TRANSCRIPTION

Previously it was shown that yeast ADA2 protein is necessary for the f ull activity of some activation domains, such as VP16 and GCN4, in viv o and in vitro. These results suggest that ADA2 protein functions as a transcriptional coactivator or adaptor that bridges the interaction b etween certain acidic activation domains and the basal transcription m achinery. Here we present two findings consistent with this model. (i) ADA2 protein interacts with a region of the VP16 acidic activation do main that requires ADA2 for activity in vivo. (ii) ADA2 protein, when fused to a heterologous DNA-binding domain, can stimulate the activity of the basal transcription factors in vivo. This ability of ADA2 to a ctivate transcription is mediated by ADA3, a gene with properties simi lar to ADA2. These findings suggest that ADA2 protein has at least som e of the properties expected of a transcriptional adaptor.