TRANSCRIPTION FACTOR (TF) IIB AND TFIIA CAN INDEPENDENTLY INCREASE THE AFFINITY OF THE TATA-BINDING PROTEIN FOR PNA

The general transcription factors (TF) IIB and TFIIA are the first factors to associate with the TATA-binding protein (TBP) during formation of a transcription initiation complex on RNA polymerase II promoters. DNase I footprint titration was used to measure the effects of TFIIB and TFIIA on binding of TBP to a consensus TATA box. Under reaction conditions optimized for TBP.DNA complex formation, the presence of TFIIB increased affinity of TBP for the TATA box by 2.5-fold, while TFIIA had no effect. When TBP binding conditions were suboptimal, both TFIIB and TFIIA independently increased TBP affinity by approximately 10-fold. Therefore both TFIIB and TFIIA have the intrinsic ability to directly increase the affinity of TBP for the TATA box. We suggest that this property of TFIIA and TFIIB may increase the range of conditions under which high affinity TBP.DNA interactions can occur and may therefore favor the formation of the preinitiation complex.