title: Heterochromatin organization of a natural yeast telomere. Changes of nucleosome distribution driven by the absence of Sir3p.
abstract: We have defined the in vivo heterochromatin structure of the left telomere of Saccharomyces cerevisiae chromosome III (LIII). Analysis of heterochromatin of a single telomere was so far lacking, due to the difficulties intrinsic to the highly repetitive nature of telomeric sequences. In LIII, the terminal (C1-3A)n repetitive sequences are followed by a complete X element and by the single copy Ty5-1 retrotransposon. Both the telosome and the X element exhibit overall resistance to micrococcal nuclease digestion reflecting their tight chromatin structure organization. The X element contains protein complexes and irregularly distributed but well localized nucleosomes. In contrast, a regular array of phased nucleosomes is associated with the promoter region of Ty5-1 and with the more centromere-proximal sequences. The lack of a structural component of yeast telomeres, the SIR3 protein, does not alter the overall tight organization of the X element but causes a nucleosome rearrangement within the promoter region of Ty5-1 and releases Ty5-1 silencing. Thus, Sir3p links the modification of the heterochromatin structure with loss of transcriptional silencing.
authors.affiliation: Fondazione Istituto Pasteur-Fondazione Cenci-Bolognetti, c/o Dipartimento di Genetica e Biologia Molecolare, Università La Sapienza, P.le Aldo Moro 5, 00185 Roma, Italy.
authors.forename: M A
authors.initials: MA
authors.lastname: Vega-Palas
authors.forename: S
authors.initials: S
authors.lastname: Venditti
authors.forename: E
authors.initials: E
authors.lastname: Di Mauro
mesh_terms: D015825:Chromosomes, Fungal / Q000737:chemistry; D004271:DNA, Fungal / Q000737:chemistry; D005656:Fungal Proteins / Q000235:genetics*; D006570:Heterochromatin / Q000737:chemistry / Q000235:genetics*; D008836:Micrococcal Nuclease; D009707:Nucleosomes / Q000235:genetics; D011401:Promoter Regions, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D018626:Retroelements; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D016615:Telomere / Q000737:chemistry / Q000235:genetics*; D015534:Trans-Activators / Q000235:genetics*
chemical_list: D004271:DNA, Fungal; D005656:Fungal Proteins; D006570:Heterochromatin; D009707:Nucleosomes; D018626:Retroelements; C084122:SIR3 protein, S cerevisiae; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D015534:Trans-Activators; D008836:Micrococcal Nuclease