Transcriptional corepression in vitro: A mot1p-associated form of TATA-Binding protein is required for repression by Leu3p

Signals from transcriptional activators to the general mRNA transcription apparatus are communicated by factors associated with RNA polymerase II or the TATA-binding protein (TBP). Currently, little is known about how gene specific transcriptional repressors communicate with RNA polymerase II. We have analyzed the requirements for repression by the Saccharomyces cerevisiae Leu3 protein (Leu3p) in a reconstituted transcription system. We have identified a complex form of TBP which is required for communication of the repressing signal. This TFIID-like complex contains a known TBP-associated protein, Mot1p, which has been implicated in the repression of a subset of yeast genes by genetic analysis. Leu3p-dependent repression can be reconstituted with purified Mot1p and recombinant TBP. In addition, a mutation in the MOT1 gene leads to partial derepression of the Leu3p-dependent LEU2 promoter, These in vivo and in vitro observations define a role for Mot1p as a transcriptional corepressor.