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Phosphorylation by CDK1 switches the function of the human SLX4 SAP domain from DNA binding to MUS81 binding

Sarah Scaglione1, Pierre-Henri Gaillard1

  • 1Aix Marseille Univ, CNRS, Inserm, Institut Paoli-Calmettes, Centre de Recherche en Cancérologie de Marseille (CRCM), Equipe Labellisée LIGUE 2025, 13009 Marseille, France.

Nucleic Acids Research
|May 14, 2026
PubMed

Insights

The SLX4 scaffold protein uses its SAP domain to bind branched DNA structures. Phosphorylation by CDK1 switches SLX4 between DNA binding and MUS81 interaction, regulating genome protection mechanisms.

Area of Science:

  • Molecular Biology
  • Genetics
  • Biochemistry

Background:

  • SLX4 is a crucial scaffold protein involved in genome protection, including homologous recombination and interstrand cross-link (ICL) repair.
  • Its functions often depend on interactions with structure-specific endonucleases like XPF-ERCC1, MUS81-EME1, and SLX1.
  • The SAP domain of SLX4 is known to mediate interaction with MUS81.

Purpose of the Study:

  • To investigate potential ancestral, MUS81-independent functions of the human SLX4 SAP domain.
  • To understand the regulatory mechanisms controlling SLX4's DNA binding and endonuclease interactions.

Main Methods:

  • Characterization of human SLX4 SAP domain DNA binding properties.
  • Analysis of SLX4 SAP phosphorylation by CDK1 and its effect on DNA binding and MUS81 interaction.
  • Creation and analysis of separation-of-function mutants affecting DNA or MUS81 binding.

Main Results:

  • Human SLX4 SAP domain binds branched DNA structures, including Holliday junctions.
  • CDK1 phosphorylation of SLX4 SAP inhibits its DNA binding while promoting MUS81 interaction.
  • Separation-of-function mutants revealed distinct roles for DNA binding versus MUS81 binding in response to different DNA damaging agents (ICLs, MMS, TOP1/PARP inhibition).

Conclusions:

  • Phosphorylation of SLX4 by CDK1 acts as a regulatory switch, balancing DNA binding and MUS81-dependent functions.
  • This switch allows SLX4 to adapt its genome protection activities to specific DNA lesions and secondary structures.
  • SLX4's dual functionality, mediated by its SAP domain, is critical for maintaining genome stability.

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