Cohabitation of insulators and silencing elements in yeast subtelomeric regions.
In budding yeast, the telomeric DNA is flanked by a combination of two subtelomeric repetitive sequences, the X and Y' elements. We have investigated the influence of these sequences on telomeric silencing. The telomere-proximal portion of either X or Y' dampened silencing when located between the telomere and the reporter gene. These elements were named STARs, for subtelomeric anti-silencing regions. STARs can also counteract silencer-driven repression at the mating-type HML locus. When two STARs bracket a reporter gene, its expression is no longer influenced by surrounding silencing elements, although these are still active on a second reporter gene. In addition, an intervening STAR uncouples the silencing of neighboring genes. STARs thus display the hallmarks of insulators. Protection from silencing is recapitulated by multimerized oligonucleotides representing Tbf1p- and Reb1p-binding sites, as found in STARs. In contrast, sequences located more centromere proximal in X and Y' elements reinforce silencing. They can promote silencing downstream of an insulated expressed domain. Overall, our results suggest that the silencing emanating from telomeres can be propagated in a discontinuous manner via a series of subtelomeric relay elements.
Fourel
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Laboratoire de Biologie Moléculaire et Cellulaire, Ecole Normale Supérieure de Lyon, UMR5665 CNRS/ENSL, 69364 Lyon Cedex 07, France.
Revardel
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Koering
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Gilson
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D001665:Binding Sites; D002503:Centromere; D015825:Chromosomes, Fungal; D004268:DNA-Binding Proteins / Q000378:metabolism; D005656:Fungal Proteins / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D008957:Models, Genetic; D011485:Protein Binding; D012091:Repetitive Sequences, Nucleic Acid; D012098:Reproduction / Q000235:genetics; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D016615:Telomere; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors
D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C065681:REB1 protein, S cerevisiae; C084121:SIR1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; C079376:TBF1 protein, S cerevisiae; D015534:Trans-Activators; D014157:Transcription Factors; C081647:high affinity DNA-binding factor, S cerevisiae