Redundant mechanisms are used by Ssn6-Tup1 in repressing chromosomal gene transcription in Saccharomyces cerevisiae.
The Ssn6-Tup1 corepressor complex regulates many genes in Saccharomyces cerevisiae. Three mechanisms have been proposed to explain its repression functions: 1) nucleosome positioning by binding histone tails; 2) recruitment of histone deacetylases; and 3) direct interference with the general transcription machinery or activators. It is unclear if Ssn6-Tup1 utilizes each of these mechanisms at a single gene in a redundant manner or each individually at different loci. A systematic analysis of the contribution of each mechanism at a native promoter has not been reported. Here we employed a genetic strategy to analyze the contributions of nucleosome positioning, histone deacetylation, and Mediator interference in the repression of chromosomal Tup1 target genes in vivo. We exploited the fact that Ssn6-Tup1 requires the ISW2 chromatin remodeling complex to establish nucleosome positioning in vivo to disrupt chromatin structure without affecting other Tup1 repression functions. Deleting ISW2, the histone deacetylase gene HDA1, or genes encoding Mediator subunits individually caused slight or no derepression of RNR3 and HUG1. However, when Mediator mutations were combined with Deltaisw2 or Deltahda1 mutations, enhanced transcription was observed, and the strongest level of derepression was observed in triple Deltaisw2/Deltahda1/Mediator mutants. The increased transcription in the mutants was not due to the loss of Tup1 at the promoter and correlated with increased TBP cross-linking to promoters. Thus, Tup1 utilizes multiple redundant mechanisms to repress transcription of native genes, which may be important for it to act as a global corepressor at a wide variety of promoters.
Zhang
Zhengjian
Z
Department of Biochemistry and Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Reese
Joseph C
JC
D000107:Acetylation; D000251:Adenosine Triphosphatases / Q000378:metabolism; D002843:Chromatin / Q000502:physiology; D015825:Chromosomes, Fungal / Q000502:physiology; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism*; D005656:Fungal Proteins / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D006655:Histone Deacetylases / Q000378:metabolism; D006657:Histones / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism*; D009707:Nucleosomes / Q000502:physiology; D012097:Repressor Proteins / Q000235:genetics* / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics* / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic / Q000502:physiology
C065455:CYC8 protein, S cerevisiae; D002843:Chromatin; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D006657:Histones; C086468:ISWI protein; D009687:Nuclear Proteins; D009707:Nucleosomes; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins; C066502:TUP1 protein, S cerevisiae; D014157:Transcription Factors; C499673:HDA1 protein, S cerevisiae; D006655:Histone Deacetylases; D000251:Adenosine Triphosphatases