An unusual form of transcriptional silencing in yeast ribosomal DNA.
Generalized transcriptional repression of large chromosomal regions in Saccharomyces cerevisiae occurs at the silent mating loci and at telomeres and is mediated by the silent information regulator (SIR) genes. We have identified a novel form of transcriptional silencing in S. cerevisiae in the ribosomal DNA (rDNA) tandem array. Ty1 retrotransposons marked with a weakened URA3 gene (Ty1-mURA3) efficiently integrated into rDNA. The mURA3 marker in rDNA was transcriptionally silenced in a SIR2-dependent manner. MET15 and LEU2 were also partially silenced, indicating that rDNA silencing may be quite general. Deletion of SIR4 enhanced mURA3 and MET15 silencing, but deletion of SIR1 or SIR3 did not affect silencing, indicating that the mechanism of silencing differs from that at telomeres and silent mating loci. Deletion of SIR2 resulted in increased psoralen cross-linking of the rDNA in vivo, suggesting that a specific chromatin structure in rDNA down-regulates polymerase II promoters.
Smith
J S
JS
Department of Molecular Biology and Genetics, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Boeke
J D
JD
D002843:Chromatin / Q000378:metabolism / Q000648:ultrastructure; D003432:Cross-Linking Reagents; D003470:Culture Media; D003547:Cysteine Synthase; D004271:DNA, Fungal / Q000235:genetics* / Q000378:metabolism; D004275:DNA, Ribosomal / Q000235:genetics* / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000235:genetics; D005656:Fungal Proteins / Q000235:genetics; D015966:Gene Expression Regulation, Fungal; D005800:Genes, Fungal; D005819:Genetic Markers; D006655:Histone Deacetylases; D009097:Multienzyme Complexes; D018626:Retroelements; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D015534:Trans-Activators / Q000235:genetics; D014158:Transcription, Genetic; D014307:Trioxsalen
D002843:Chromatin; D003432:Cross-Linking Reagents; D003470:Culture Media; D004271:DNA, Fungal; D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; D005819:Genetic Markers; D009097:Multienzyme Complexes; D018626:Retroelements; D029701:Saccharomyces cerevisiae Proteins; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D015534:Trans-Activators; D003547:Cysteine Synthase; C103381:MET17 protein, S cerevisiae; C087778:SIR2 protein, S cerevisiae; D056565:Sirtuin 2; D037761:Sirtuins; D006655:Histone Deacetylases; D014307:Trioxsalen