TFIIA regulates TBP and TFIID dimers

Dimerization of the TATA-binding protein (TBP) through its DNA-binding doma in blocks TBP from accessing DNA and prevents unregulated gene expression. TFIIA plays a central role in loading TBP and its multisubunit counterpart TFIID onto promoter DNA, and it is therefore a candidate for regulating TBP /TFIID dimerization. Here, we show that TFIIA promotes the dissociation of TBP dimers directly and in doing so accelerates the kinetics of DNA binding . TFIID dimer dissociation was found to be slow and rate limiting in DNA bi nding. TFIIA induced a rapid dissociation of TFIID dimers, allowing TFIID t o readily load onto promoter DNA. Together, these results suggest a novel m echanism by which TFIIA assists in regulating gene expression.