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A divalent FHA/BRCT-binding mechanism couples the MRE11-RAD50-NBS1 complex to damaged chromatin

Flurina J Hari1, Christoph Spycher, Stephanie Jungmichel

  • 1Institute of Veterinary Biochemistry and Molecular Biology, University of Zurich, Zurich, Switzerland.

EMBO Reports
|March 13, 2010
PubMed

Insights

The Nijmegen breakage syndrome 1 (NBS1) protein binds to mediator of the DNA damage checkpoint 1 (MDC1) via its FHA and BRCT domains. However, only FHA domain binding is essential for DNA damage repair and G2/M checkpoint activation.

Area of Science:

  • Molecular Biology
  • Cell Biology
  • Genetics

Background:

  • The MRE11-RAD50-NBS1 (MRN) complex is crucial for DNA double-strand break repair.
  • MRN complex recruitment to damage sites involves NBS1 binding to phosphorylated mediator of the DNA damage checkpoint 1 (MDC1).
  • NBS1 possesses FHA and BRCT domains at its amino terminus.

Purpose of the Study:

  • To investigate the role of NBS1's FHA and BRCT domains in MDC1 interaction.
  • To determine the functional significance of MRN complex accumulation at DNA damage sites for checkpoint activation.

Main Methods:

  • Site-directed mutagenesis of NBS1 FHA and BRCT domains.
  • Analysis of MRN complex localization at DNA double-strand breaks.
  • Assessment of G2/M cell cycle checkpoint activation.

Main Results:

  • Both FHA and BRCT domains of NBS1 interact with phosphorylated MDC1.
  • Mutations in FHA or BRCT domains impair MRN accumulation at DNA damage sites.
  • Only FHA domain mutations, not BRCT mutations, result in a G2/M checkpoint defect.

Conclusions:

  • MDC1-dependent MRN chromatin accumulation is not essential for G2/M checkpoint activation.
  • The FHA domain of NBS1 plays a critical role in both MDC1 interaction and G2/M checkpoint control.

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