QUANTITATION OF PUTATIVE ACTIVATOR-TARGET AFFINITIES PREDICTS TRANSCRIPTIONAL ACTIVATING POTENTIALS

We quantitate the 'activating potentials' of deletion and point mutati on variants of a 42 amino acid yeast transcriptional activating region excised from the yeast activator GAL4 and, using surface plasmon reso nance, we measure the relative affinities of these molecules for a var iety of proteins, including plausible target proteins as well as GAL80 , a specific inhibitor of GAL4. We fond a remarkable correlation betwe en the relative activating potentials of the derivatives and their rel ative affinities for yeast TBP and for yeast TFIIB; other tested prote ins interacted significantly more weakly, if at all. These results pro vide an especially strong argument that TBP and TFIIB are activating r egion targets. We also show, using one set of yeast activating region mutants, that activator-target interactions are strongly correlated wi th the length of the activating region, that the effect of point mutan ts is highly dependent on the length of the activating region mutated and that, unlike interactions with TBP and TFIIB, interaction with the specific inhibitor GAL80 is destroyed by deletion of certain critical residues in the C-terminal half of the 42 amino acid activating regio n.