The evolutionarily conserved shelterin complex has been shown to play both positive and negative roles in telomerase regulation in mammals and fission yeast. Although shelterin prevents the checkpoint kinases ATM and ATR from fully activating DNA damage responses at telomeres in mammalian cells, those kinases also promote telomere maintenance. In fission yeast, cells lacking both Tel1 (ATM ortholog) and Rad3 (ATR ortholog) fail to recruit telomerase to telomeres and survive by circularizing chromosomes. However, the critical telomere substrate(s) of Tel1ATM and Rad3ATR was unknown. Here we show that phosphorylation of the shelterin subunit Ccq1 on Thr93, redundantly mediated by Tel1ATM and/or Rad3ATR, is essential for telomerase association with telomeres. In addition, we show that the telomerase subunit Est1 interacts directly with the phosphorylated Thr93 of Ccq1 to ensure telomere maintenance. The shelterin subunits Taz1, Rap1 and Poz1 (previously established inhibitors of telomerase) were also found to negatively regulate Ccq1 phosphorylation. These findings establish Tel1ATM/Rad3ATR-dependent Ccq1 Thr93 phosphorylation as a critical regulator of telomere maintenance in fission yeast.
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We thank F. Ishikawa (Kyoto University), J.P. Cooper (Cancer Research UK), M.R. Flory (Mendel Biotechnology, Inc.), V.A. Zakian (Princeton University), A.M. Carr (University of Sussex) and P. Russell (The Scripps Research Institute) for sharing published strains and plasmids, L. Khair for her initial efforts to generate yeast strains and reagents used in this study, and P. Baumann (Stowers Institute) for generously sharing his unpublished anti-Ccq1 antibody. We also thank F. Ishikawa for communicating unpublished results. J.K. was supported in part by the Federal Work-Study program. This work was supported by US National Institutes of Health grant GM078253 (T.M.N.).
The authors declare no competing financial interests.
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Moser, B., Chang, YT., Kosti, J. et al. Tel1ATM and Rad3ATR kinases promote Ccq1-Est1 interaction to maintain telomeres in fission yeast. Nat Struct Mol Biol 18, 1408–1413 (2011). https://doi.org/10.1038/nsmb.2187
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