title: Differential nuclear localization does not determine the silencing status of Saccharomyces cerevisiae telomeres.
abstract: In Saccharomyces cerevisiae, genes near telomeres are transcriptionally repressed, a phenomenon termed telomere position effect (TPE). Yeast telomeres cluster near the nuclear periphery, as do foci of proteins essential for TPE: Rap1p, Sir2-4p, and yKu70p/yKu80p. However, it is not clear if localization of telomeres to the periphery actually contributes to TPE. We examined the localization patterns of two telomeres with different levels of TPE: truncated VII-L and native VI-R. For both telomeres, localization to the nuclear periphery or to the silencing foci was neither necessary nor sufficient for TPE. Moreover, there was no correlation between TPE levels and the extent of localization. Tethering the truncated VII-L telomere to the nuclear periphery resulted in a modest increase in TPE. However, tethering did not bypass the roles of yKu70p, Sir4p, or Esc1p in TPE. Using mutations in RIF genes that bypass the role of Ku in TPE, a correlation between the level of silencing and the number of Rap1p foci present in the nucleus was observed, suggesting that Sir protein levels at telomeres determine both the level of TPE and the number of foci.
authors: Department of Molecular Biology, Princeton University, Princeton, New Jersey 08544, USA.
authors: Michelle A
authors: MA
authors: Mondoux
authors: Jillian G
authors: JG
authors: Scaife
authors: Virginia A
authors: VA
authors: Zakian
mesh_terms: D002467:Cell Nucleus; D004268:DNA-Binding Proteins / Q000502:physiology; D015966:Gene Expression Regulation, Fungal; D009687:Nuclear Proteins; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000502:physiology; D000089804:Shelterin Complex; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae / Q000502:physiology; D016615:Telomere / Q000737:chemistry*; D034501:Telomere-Binding Proteins / Q000502:physiology; D014157:Transcription Factors / Q000502:physiology
chemical_list: D004268:DNA-Binding Proteins; D009687:Nuclear Proteins; C440829:RAP1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D000089804:Shelterin Complex; D038281:Silent Information Regulator Proteins, Saccharomyces cerevisiae; D034501:Telomere-Binding Proteins; D014157:Transcription Factors; C520769:YKU70 protein, S cerevisiae; C520770:YKU80 protein, S cerevisiae