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 novel mechanism. Biochemical analyses reveal that Dr(1) directly interacts with the multiprotein TFIID complex. By use of the yeast two-hybrid system, we demonstrate that the association of Dr(1) with the TATA-binding protein (TBP) subunit of TFIID occurs in vivo. In addition, Dr(1) can repress transcription from TATA-containing as well as TATA-less promoters in transient transfection assays. Importantly, Dr(1)-mediated repression can be reversed by overexpression of TBP in vivo. By use of 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 of Dr(1) cannot be replaced by a heterologous DNA-binding domain in mediating repression. We demonstrate that some, but not all, transcriptional activators can reverse Dr(1)-mediated repression in vivo.