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  • The EMBO Journal (2008) 27, 2400 - 2410
  • doi:10.1038/emboj.2008.171

Published online: 28 August 2008

Checkpoint-dependent phosphorylation of Exo1 modulates the DNA damage responseEMBO Open

Isabelle Morin1,a, Hien-Ping Ngo1,a, Amanda Greenall1,2, Mikhajlo K Zubko1,3, Nick Morrice4 and David Lydall1,2,5

  1. Institute for Ageing and Health, Henry Wellcome Laboratory for Biogerontology Research, Newcastle University, Newcastle Upon Tyne, UK
  2. Centre for Integrated Systems Biology of Ageing and Nutrition, Henry Wellcome Laboratory for Biogerontology Research, Newcastle University, Newcastle Upon Tyne, UK
  3. Division of Biology, School of Biology, Chemistry & Health Science, Faculty of Science and Engineering, Manchester Metropolitan University, Manchester, UK
  4. MRC Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dundee, UK
  5. Institute for Cell and Molecular Biosciences, Henry Wellcome Laboratory for Biogerontology Research, Newcastle University, Newcastle Upon Tyne, UK

Correspondence to:

David Lydall, Institute for Ageing and Health, Henry Wellcome Laboratory for Biogerontology Research, Newcastle University, Newcastle Upon Tyne NE4 6BE, UK. Tel.: +44 191 256 3449; Fax: +44 191 256 3445; E-mail: D.A.Lydall@ncl.ac.uk

aJoint first authors

Received 3 December 2007; Accepted 30 July 2008

Exo1 is a nuclease involved in mismatch repair, DSB repair, stalled replication fork processing and in the DNA damage response triggered by dysfunctional telomeres. In budding yeast and mice, Exo1 creates single-stranded DNA (ssDNA) at uncapped telomeres. This ssDNA accumulation activates the checkpoint response resulting in cell cycle arrest. Here, we demonstrate that Exo1 is phosphorylated when telomeres are uncapped in cdc13-1 and yku70Delta yeast cells, and in response to the induction of DNA damage. After telomere uncapping, Exo1 phosphorylation depends on components of the checkpoint machinery such as Rad24, Rad17, Rad9, Rad53 and Mec1, but is largely independent of Chk1, Tel1 and Dun1. Serines S372, S567, S587 and S692 of Exo1 were identified as targets for phosphorylation. Furthermore, mutation of these Exo1 residues altered the DNA damage response to uncapped telomeres and camptothecin treatment, in a manner that suggests Exo1 phosphorylation inhibits its activity. We propose that Rad53-dependent Exo1 phosphorylation is involved in a negative feedback loop to limit ssDNA accumulation and DNA damage checkpoint activation.

  • Keywords:

    • cdc13-1,
    • checkpoint,
    • Exo1,
    • phosphorylation,
    • telomere

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The EMBO Journal is published by Nature Publishing Group on behalf of European Molecular Biology Organization