THE TATA ELEMENT AND ITS CONTEXT AFFECT THE COOPERATIVE INTERACTION OF TATA-BINDING PROTEIN WITH THE TFIIB-RELATED FACTOR, TFIIIB70

We have conducted a quantitative thermodynamic study of the effects of the TATA element and TATA-flanking sequences on the assembly of compl exes containing TATA-binding protein (TBP) and the TFIIB-related facto r, TFIIIB70. TBP binds to the sequence TATAAAAG in the context of the yeast U6 gene (yU6 hybrid TATA) or the adenovirus major late promoter (AdMLP) with different affinities demonstrating that the sequence cont ext of a TATA element contributes to TBP binding, We also determined t he cooperative free energies of formation of TBP.TFIIIB70.DNA complexe s on the yU6 TATA element, the yU6 hybrid TATA element and a nonconsen sus TATA element, The yU6 hybrid TATA displayed a moderate, less than 5-fold, increase in TBP affinity similar to the 3-fold increase observ ed for the AdMLP. In contrast, the nonconsensus and yU6 TATAs increase d the affinity of TBP for DNA 12- and 17-fold, respectively. Since the TBP-TFIIIB70 cooperativity is greater on lower affinity TATA boxes an d most polymerase III genes contain low affinity ''TATA boxes,'' we co nclude that the cooperative binding of TFIIIB70 and TBP to DNA represe nts an important driving force in the assembly of polymerase III-speci fic transcription complexes, An effect of the sequences surrounding th e TATA box was also observed on TBP-TFIIIB70 cooperativity, The mechan istic implications of the thermodynamic linkage between DNA sequence a nd binding cooperativity are discussed.