THE ACTIVATION DOMAIN OF GAL4 PROTEIN MEDIATES COOPERATIVE PROMOTER-BINDING WITH GENERAL TRANSCRIPTION FACTORS IN-VIVO

Most proteins that activate RNA polymerase II-mediated transcription i n eukaryotic cells contain sequence-specific DNA-binding domains and ' 'activation'' regions. The latter bind general transcription factors a nd/or coactivators and are required for high-level transcription. Thei r function in vivo is unknown. Since several activation domains bind t he TATA-binding protein (TBP), TBP-associated factors, or other genera l factors in vitro, one role of the activation domain may be to facili tate promoter occupancy by supporting cooperative binding of the activ ator and general transcription factors. Using the GAL4 system of yeast , we have tested this model in vivo. It is demonstrated that the prese nce of a TATA box (the TBP binding site) facilitates binding of GAL4 p rotein to low- and moderate-affinity sites and that the activation dom ain modulates these effects. These results support the cooperative bin ding model for activation domain function in vivo.