title: Functional dissection of the yeast Cyc8-Tup1 transcriptional co-repressor complex.
abstract: DNA-binding repressor proteins mediate regulation of yeast genes by cell type (Mcm1/alpha 2 and a1/alpha 2), glucose (Mig1) and oxygen (Rox1) (refs 1-4 respectively). An unusual feature of all these regulatory pathways is that transcriptional repression requires two physically associated proteins that do not bind DNA Cyc8(Ssn6) and Tup1. The Cyc8-Tup1 complex has been proposed to be a co-repressor that is recruited to target promoters by pathway-specific DNA-binding proteins, but the specific functions of the individual proteins are unknown. Here we show that when it is bound upstream of a functional promoter through the LexA DNA-binding domain, Tup1 represses transcription in the absence of Cyc8. Deletion analysis indicates that Tup1 contains at least two non-overlapping transcriptional repression regions with minimal primary sequence similarity, and a separable Cyc8-interaction domain. These Tup1 domains, which do not include the beta-transducin motifs, are necessary and partially sufficient for Tup1 function. We suggest that Tup1 performs the repression function of the Cyc8-Tup1 co-repressor complex, and that Cyc8 serves as a link with the pathway-specific DNA-binding proteins.
authors.affiliation: Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts 02115.
authors.forename: D
authors.initials: D
authors.lastname: Tzamarias
authors.forename: K
authors.initials: K
authors.lastname: Struhl
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000378:metabolism; D001483:Base Sequence; D003001:Cloning, Molecular; D004271:DNA, Fungal / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D011401:Promoter Regions, Genetic; D012097:Repressor Proteins / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D029701:Saccharomyces cerevisiae Proteins; D017384:Sequence Deletion; D012697:Serine Endopeptidases; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000378:metabolism; D000099160:LexA Repressor Protein
chemical_list: D001426:Bacterial Proteins; D004271:DNA, Fungal; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; D012697:Serine Endopeptidases; D001616:beta-Galactosidase; D000099160:LexA Repressor Protein; C065455:CYC8 protein, S cerevisiae; C066502:TUP1 protein, S cerevisiae