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The principal role of Ku in telomere length maintenance is promotion of Est1 association with telomeres.

Williams JM, Ouenzar F, Lemon LD, Chartrand P, Bertuch AA - Genetics (2014)

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.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030.

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Related in: MedlinePlus

Telomerase overexpression or Cdc13-Est2 expression has differential effects in WT, yku80-135i, and yku80∆ strains. (A) Telomere length analysis by Southern blot of XhoI-digested DNA isolated from WT, yku80-135i, and yku80∆ strains transformed with Est1 and Est2 overexpression plasmids, singly and in combination. (B) Telomere length analysis by Southern blotting of 1×–4× serial single-colony streakouts of WT, yku80-135i, and yku80∆ strains simultaneously overexpressing Est1, Est2, and TLC1. (C) Telomere length analysis of 1×–5× serial single-colony streakouts of cdc13∆ (WT), cdc13∆ yku80-135i (yku80-135i), and cdc13∆ yku80∆ (yku80∆) strains expressing a Cdc13–Est2 fusion.
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fig1: Telomerase overexpression or Cdc13-Est2 expression has differential effects in WT, yku80-135i, and yku80∆ strains. (A) Telomere length analysis by Southern blot of XhoI-digested DNA isolated from WT, yku80-135i, and yku80∆ strains transformed with Est1 and Est2 overexpression plasmids, singly and in combination. (B) Telomere length analysis by Southern blotting of 1×–4× serial single-colony streakouts of WT, yku80-135i, and yku80∆ strains simultaneously overexpressing Est1, Est2, and TLC1. (C) Telomere length analysis of 1×–5× serial single-colony streakouts of cdc13∆ (WT), cdc13∆ yku80-135i (yku80-135i), and cdc13∆ yku80∆ (yku80∆) strains expressing a Cdc13–Est2 fusion.

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.


The principal role of Ku in telomere length maintenance is promotion of Est1 association with telomeres.

Williams JM, Ouenzar F, Lemon LD, Chartrand P, Bertuch AA - Genetics (2014)

Telomerase overexpression or Cdc13-Est2 expression has differential effects in WT, yku80-135i, and yku80∆ strains. (A) Telomere length analysis by Southern blot of XhoI-digested DNA isolated from WT, yku80-135i, and yku80∆ strains transformed with Est1 and Est2 overexpression plasmids, singly and in combination. (B) Telomere length analysis by Southern blotting of 1×–4× serial single-colony streakouts of WT, yku80-135i, and yku80∆ strains simultaneously overexpressing Est1, Est2, and TLC1. (C) Telomere length analysis of 1×–5× serial single-colony streakouts of cdc13∆ (WT), cdc13∆ yku80-135i (yku80-135i), and cdc13∆ yku80∆ (yku80∆) strains expressing a Cdc13–Est2 fusion.
© Copyright Policy - open-access
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4125388&req=5

fig1: Telomerase overexpression or Cdc13-Est2 expression has differential effects in WT, yku80-135i, and yku80∆ strains. (A) Telomere length analysis by Southern blot of XhoI-digested DNA isolated from WT, yku80-135i, and yku80∆ strains transformed with Est1 and Est2 overexpression plasmids, singly and in combination. (B) Telomere length analysis by Southern blotting of 1×–4× serial single-colony streakouts of WT, yku80-135i, and yku80∆ strains simultaneously overexpressing Est1, Est2, and TLC1. (C) Telomere length analysis of 1×–5× serial single-colony streakouts of cdc13∆ (WT), cdc13∆ yku80-135i (yku80-135i), and cdc13∆ yku80∆ (yku80∆) strains expressing a Cdc13–Est2 fusion.
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.

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.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas 77030.

Show MeSH
Related in: MedlinePlus