Thermodynamic studies of the interaction of the Saccharomyces cerevisiae TATA binding protein with transcription factor IIB

The initiation of transcription from promoters transcribed by RNA polymerase I! starts with the binding of the TATA binding protein (TBP), as part of the TFIID complex, to a "TATA box" DMA sequence. Transcription Factor IIB (TFIIB) and then RNA polymerase are subsequently recruited to the promoter. TFIIB by itself does not interact with DMA although biochemical and crystallographic studies have established the formation and structure of a ternary DNA-TBP-TFIIB complex. In order to investigate how the physical properties of TFIIB determine its biological function an analysis. of the cooperative interactions between TBP and TFIIB upon TATA box binding is being conducted. Three-fold TBP-TFIIB cooperativity is observed by a series of TBP titrations conducted at increasing concentrations, to saturating, of TFIIB at pH 7.0, 25mM BisTris, 5mM MgCI2, 1mM CaCI2 2mM DTT 1ng/ml poly (dG-dC) 0.01% Brij 58, 100mM KCI, 30° C. This moderate cooperativity is consistent with the reported lability of TFIIB binding during transcription initiation, elongation and re-initiation [Roberts, S.G.E et al. (1995) Current Biology 5. 508]. A decrease in [KCI] results in an increase in the TBP-TFIIB cooperativity, consistent with the predominantly electrostatic interactions inferred from the crystal structure of a TATA-TBP-TFIIB complex [Nikolov, D. B. et el.(1995) Nature 377, 119].