STRUCTURE-FUNCTION ANALYSIS OF THE TBP-BINDING PROTEIN DR(1) REVEALS A MECHANISM FOR REPRESSION OF CLASS-II GENE-TRANSCRIPTION

Dr(1), a repressor of class II genes, regulates transcription by a nov el mechanism. Biochemical analyses reveal that Dr(1) directly interact s with the multiprotein TFIID complex. By use of the yeast two-hybrid system, we demonstrate that the association of Dr(1) with the TATA-bin ding protein (TBP) subunit of TFIID occurs in vivo. In addition, Dr(1) can repress transcription from TATA-containing as well as TATA-less p romoters in transient transfection assays. Importantly, Dr(1)-mediated repression can be reversed by overexpression of TBP in vivo. By use o f diverse approaches, we mapped two distinct domains in Dr(1) required for repression. One domain is essential for the Dr(1)-TBP interaction , and the second is rich in alanine residues. The TBP-binding domain o f Dr(1) cannot be replaced by a heterologous DNA-binding domain in med iating repression. We demonstrate that some, but not all, transcriptio nal activators can reverse Dr(1)-mediated repression in vivo.