Limitations of silencing at native yeast telomeres.
Silencing at native yeast telomeres, in which the subtelomeric elements are intact, is different from silencing at terminal truncations. The repression of URA3 inserted in different subtelomeric positions at several chromosome ends was investigated. Many ends exhibit very little silencing close to the telomere, while others exhibit substantial repression in limited domains. Silencing at native ends is discontinuous, with maximal repression found adjacent to the ARS consensus sequence in the subtelomeric core X element. The level of repression declines precipitously towards the centromere. Mutation of the ARS sequence or an adjacent Abf1p-binding site significantly reduces silencing. The subtelomeric Y' elements are resistant to silencing along their whole length, yet silencing can be re-established at the proximal X element. Deletion of PPR1, the transactivator of URA3, and SIR3 overexpression do not increase repression or extend spreading of silencing to the same extent as with terminally truncated ends. sir1Delta causes partial derepression at X-ACS, in contrast to the lack of effect seen at terminal truncations. orc2-1 and orc5-1 have no effect on natural silencing yet cause derepression at truncated ends. X-ACS silencing requires the proximity of the telomere and is dependent on SIR2, SIR3, SIR4 and HDF1. The structures found at native yeast telomeres appear to limit the potential of repressive chromatin.
Pryde
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Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK.
Louis
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EJ
D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002843:Chromatin / Q000378:metabolism; D016384:Consensus Sequence; D004268:DNA-Binding Proteins / Q000378:metabolism; D005656:Fungal Proteins / Q000235:genetics*; D015966:Gene Expression Regulation, Fungal; D008957:Models, Genetic; D008969:Molecular Sequence Data; D009154:Mutation; D051738:Origin Recognition Complex; D011485:Protein Binding; D011995:Recombination, Genetic; D012091:Repetitive Sequences, Nucleic Acid; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D016615:Telomere; D015534:Trans-Activators / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism
C061886:ABF1 protein, S cerevisiae; D002843:Chromatin; D004268:DNA-Binding Proteins; D005656:Fungal Proteins; C497215:ORC2 protein, S cerevisiae; D051738:Origin Recognition Complex; D029701:Saccharomyces cerevisiae Proteins; D015534:Trans-Activators; D014157:Transcription Factors; C520769:YKU70 protein, S cerevisiae; C081647:high affinity DNA-binding factor, S cerevisiae