High-affinity DNA binding by a Mot1p-TBP complex: implications for TAF-independent transcription

Yeast Mot1p, an abundant conserved member of the Snf2p-ATPase family of proteins, both dissociates TBP from DNA in vitro using the energy of ATP and represses gene transcription in vivo, yet paradoxically, loss of Mot1p function also leads to decreased transcription of certain genes. We conducted experiments utilizing fluorescently labeled DNA, TBP, fluorescence anisotropy spectroscopy and native gel electrophoresis to study Mot1p action. We have made a number of observations, the most intriguing being that a stable Mot1p-TBP complex has the ability to bind TATA DNA with high affinity, albeit with dramatically altered specificity. We propose that this altered TBP-DNA recognition is integral to Mot1p's ability to regulate transcription, and further postulate that the Mot1p-TBP complex delivers TBP to TAF-independent mRNA encoding genes.