Silenced chromatin is permissive to activator binding and PIC recruitment.
Chromatin is thought to repress transcription by limiting access of the DNA to transcription factors. Using a yeast heat shock gene flanked by mating-type silencers as a model system, we find that repressive, SIR-generated heterochromatin is permissive to the constitutive binding of an activator, HSF, and two components of the preinitiation complex (PIC), TBP and Pol II. These factors cohabitate the promoter with Sir silencing proteins and deacetylated nucleosomal histones. The heterochromatic HMRa1 promoter is also occupied by TBP and Pol II, suggesting that SIR regulates gene expression not by restricting factor access to DNA but rather by blocking a step downstream of PIC recruitment. Interestingly, activation of silent promoter chromatin occurs in the absence of histone displacement and without change in histone acetylation state.
Sekinger
E A
EA
Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, Shreveport, LA 71130, USA.
Gross
D S
DS
D002843:Chromatin / Q000235:genetics* / Q000378:metabolism; D004257:DNA Polymerase II / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics* / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D020868:Gene Silencing; D005809:Genes, Regulator / Q000235:genetics; D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins / Q000235:genetics* / Q000378:metabolism; D006655:Histone Deacetylases / Q000235:genetics / Q000378:metabolism; D011233:Precipitin Tests; D011401:Promoter Regions, Genetic / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D035181:TATA-Box Binding Protein; D015534:Trans-Activators / Q000235:genetics / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics* / Q000378:metabolism; D014158:Transcription, Genetic / Q000235:genetics*
D002843:Chromatin; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C067168:HSF1 protein, S cerevisiae; C074510:HSP82 protein, S cerevisiae; D018841:HSP90 Heat-Shock Proteins; D006360:Heat-Shock Proteins; C084122:SIR3 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D035181:TATA-Box Binding Protein; D015534:Trans-Activators; D014157:Transcription Factors; D004257:DNA Polymerase II; C087778:SIR2 protein, S cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D006655:Histone Deacetylases