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Sae2 integrates CDK and checkpoint phosphorylation to coordinate MRX cleavage with checkpoint attenuation

Erika Casari1, Marco Gnugnoli1, Paolo Pizzul1

  • 1Dipartimento di Biotecnologie e Bioscienze, Università degli Studi di Milano-Bicocca, Milano, Italy.

Communications Biology
|December 24, 2025
PubMed

Insights

Yeast Sae2 phosphorylation by Mec1/Tel1 kinases restrains the Rad53 DNA damage response. T279 phosphorylation also promotes DNA repair, particularly for meiotic double-strand breaks.

Area of Science:

  • Molecular Biology
  • Cellular Biology
  • Biochemistry

Background:

  • Yeast Sae2 protein has a dual role in DNA damage response.
  • It suppresses Rad53 activation and aids DNA end processing by the MRX complex.

Purpose of the Study:

  • To elucidate the regulatory mechanisms of Sae2 in the DNA damage response.
  • To investigate the roles of Sae2 phosphorylation at T90 and T279 in regulating Rad53 and DNA repair.

Main Methods:

  • AlphaFold3-based structural modeling.
  • Site-directed mutagenesis and phosphomimetic analysis.
  • Analysis of DNA damage checkpoint activation and DNA repair processes.

Main Results:

  • Mec1/Tel1-dependent phosphorylation of Sae2 at T90 or T279 inhibits Rad9-Rad53 interaction and Rad53 activation.
  • Non-phosphorylatable Sae2 mutants (T90A T279A) show persistent Rad53 activation.
  • Phosphomimetic Sae2 variants (T90E, T279E) restore normal checkpoint inactivation.
  • Electrostatic interactions between phosphorylated Sae2 (T90/T279) and Rad53 (R70) are crucial for regulation.
  • T279 phosphorylation, alongside CDK-dependent S267 phosphorylation, promotes MRX-mediated hairpin resolution and meiotic DSB processing.
  • A Sae2 T279E mutant partially rescues hairpin cleavage defects and DNA damage sensitivity in tel1Δ cells.

Conclusions:

  • Sae2 phosphorylation at T90/T279 is a key mechanism for inhibiting the Rad53 DNA damage response.
  • Tel1 kinase primarily promotes MRX activity via Sae2 T279 phosphorylation.
  • Sae2 T279 phosphorylation is critical for processing meiotic double-strand breaks and resolving DNA hairpin structures.

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