title: The principal role of Ku in telomere length maintenance is promotion of Est1 association with telomeres.
abstract: Telomere length is tightly regulated in cells that express telomerase. The Saccharomyces cerevisiae Ku heterodimer, a DNA end-binding complex, positively regulates telomere length in a telomerase-dependent manner. Ku associates with the telomerase RNA subunit TLC1, and this association is required for TLC1 nuclear retention. Ku-TLC1 interaction also impacts the cell-cycle-regulated association of the telomerase catalytic subunit Est2 to telomeres. The promotion of TLC1 nuclear localization and Est2 recruitment have been proposed to be the principal role of Ku in telomere length maintenance, but neither model has been directly tested. Here we study the impact of forced recruitment of Est2 to telomeres on telomere length in the absence of Ku's ability to bind TLC1 or DNA ends. We show that tethering Est2 to telomeres does not promote efficient telomere elongation in the absence of Ku-TLC1 interaction or DNA end binding. Moreover, restoration of TLC1 nuclear localization, even when combined with Est2 recruitment, does not bypass the role of Ku. In contrast, forced recruitment of Est1, which has roles in telomerase recruitment and activation, to telomeres promotes efficient and progressive telomere elongation in the absence of Ku-TLC1 interaction, Ku DNA end binding, or Ku altogether. Ku associates with Est1 and Est2 in a TLC1-dependent manner and enhances Est1 recruitment to telomeres independently of Est2. Together, our results unexpectedly demonstrate that the principal role of Ku in telomere length maintenance is to promote the association of Est1 with telomeres, which may in turn allow for efficient recruitment and activation of the telomerase holoenzyme.
authors.affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030.
authors.forename: Jaime M
authors.initials: JM
authors.lastname: Williams
authors.affiliation: Department of Biochemistry, Université de Montréal, Montréal, Québec, Canada H3C 3J7.
authors.forename: Faissal
authors.initials: F
authors.lastname: Ouenzar
authors.affiliation: Integrative Molecular and Biomedical Sciences Graduate Program, Baylor College of Medicine, Houston, Texas 77030.
authors.forename: Laramie D
authors.initials: LD
authors.lastname: Lemon
authors.affiliation: Department of Biochemistry, Université de Montréal, Montréal, Québec, Canada H3C 3J7.
authors.forename: Pascal
authors.initials: P
authors.lastname: Chartrand
authors.affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030 Integrative Molecular and Biomedical Sciences Graduate Program, Baylor College of Medicine, Houston, Texas 77030 Department of Pediatrics, Baylor College of Medicine, Houston, Texas 77030 abertuch@bcm.edu.
authors.forename: Alison A
authors.initials: AA
authors.lastname: Bertuch
mesh_terms: D004271:DNA, Fungal / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D007091:Image Processing, Computer-Assisted; D017404:In Situ Hybridization, Fluorescence; D011401:Promoter Regions, Genetic; D012441:Saccharomyces cerevisiae / Q000235:genetics*; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D019098:Telomerase / Q000235:genetics / Q000378:metabolism*; D016615:Telomere / Q000378:metabolism*; D059505:Telomere Homeostasis / Q000235:genetics*
chemical_list: D004271:DNA, Fungal; D004268:DNA-Binding Proteins; D029701:Saccharomyces cerevisiae Proteins; C520769:YKU70 protein, S cerevisiae; C520770:YKU80 protein, S cerevisiae; C099024:EST1 protein, S cerevisiae; C509185:EST2 protein, S cerevisiae; D019098:Telomerase
keywords: Est1; Est2; Ku; TLC1; telomerase; telomere