The principal role of Ku in telomere length maintenance is promotion of Est1 association with telomeres.
Bottom Line: 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.Moreover, restoration of TLC1 nuclear localization, even when combined with Est2 recruitment, does not bypass the role of Ku.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.
Affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030.Show MeSH
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Mentions: We first sought to determine whether reduced amounts of Est2 at telomeres played a major role in the telomere shortening observed in the absence of Ku or Ku–TLC1 interaction. To do this, we overexpressed Est2 and Est1 subunits in an attempt to drive more telomerase to telomeres. We found that Est2 overexpression had no impact on telomere length in yku80-135i or, as previously reported, in yku80∆ strains (Figure 1A and Supporting Information, Figure S1) (Teo and Jackson 2001). As previously reported, a slight increase in telomere length was observed when Est1 was overexpressed in WT strains (Virta-Pearlman et al. 1996; Zhang et al. 2010), and a similar effect was observed in yku80-135i and yku80∆ strains. However, in contrast to WT strains, where simultaneous overexpression of Est1 and Est2 resulted in synergistic telomere elongation, Est1/Est2 co-overexpression had minimal impact on telomere length in the yku80-135i mutant or in the absence of Ku, as telomeres were no longer than when Est1 was overexpressed alone (Figure 1A and Figure S1). Since telomere elongation was minimal when Est2 was overexpressed alone or in combination with Est1, these results suggest that reduced amounts of Est2 at telomeres in the absence of Ku–TLC1 interaction may not be the main reason that telomeres are short.
Affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030.