Varying the number of telomere-bound proteins does not alter telomere length in tel1Delta cells.
Yeast telomere DNA consists of a continuous, approximately 330-bp tract of the heterogeneous repeat TG(1-3) with irregularly spaced, high affinity sites for the protein Rap1p. Yeast monitor, or count, the number of telomeric Rap1p C termini in a negative feedback mechanism to modulate the length of the terminal TG(1-3) repeats, and synthetic telomeres that tether Rap1p molecules adjacent to the TG(1-3) tract cause wild-type cells to maintain a shorter TG(1-3) tract. To identify trans-acting proteins required to count Rap1p molecules, these same synthetic telomeres were placed in two short telomere mutants: yku70Delta (which lack the yeast Ku70 protein) and tel1Delta (which lack the yeast ortholog of ATM). Although both mutants maintain telomeres with approximately 100 bp of TG(1-3), only yku70Delta cells maintained shorter TG(1-3) repeats in response to internal Rap1p molecules. This distinct response to internal Rap1p molecules was not caused by a variation in Rap1p site density in the TG(1-3) repeats as sequencing of tel1Delta and yku70Delta telomeres showed that both strains have only five to six Rap1p sites per 100-bp telomere. In addition, the tel1Delta short telomere phenotype was epistatic to the unregulated telomere length caused by deletion of the Rap1p C-terminal domain. Thus, the length of the TG(1-3) repeats in tel1Delta cells was independent of the number of the Rap1p C termini at the telomere. These data indicate that tel1Delta cells use an alternative mechanism to regulate telomere length that is distinct from monitoring the number of telomere binding proteins.
Ray
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Lerner Research Institute, Cleveland Clinic Foundation, Department of Molecular Biology, NC20, 9500 Euclid Avenue, Cleveland, OH 44195, USA.
Runge
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KW
D001665:Binding Sites; D003001:Cloning, Molecular; D004268:DNA-Binding Proteins / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins; D017422:Sequence Analysis, DNA; D000089804:Shelterin Complex; D019098:Telomerase; D016615:Telomere / Q000235:genetics* / Q000378:metabolism*; D034501:Telomere-Binding Proteins; D014157:Transcription Factors
D004268:DNA-Binding Proteins; C440829:RAP1 protein, S cerevisiae; D029701:Saccharomyces cerevisiae Proteins; D000089804:Shelterin Complex; D034501:Telomere-Binding Proteins; D014157:Transcription Factors; D019098:Telomerase