Checkpoint activation in response to double-strand breaks requires the Mre11/Rad50/Xrs2 complex

Area of Science:

• Molecular Biology
• Cellular Biology
• Genetics

Background:

• The Mre11/Rad50/NBS1 complex in humans is implicated in DNA double-strand break (DSB) repair and DNA damage checkpoint activation.
• The homologous budding yeast complex, Mre11/Rad50/Xrs2, has been investigated for its role in checkpoint activation following DSBs.

Purpose of the Study:

• To investigate the role of the Mre11/Rad50/Xrs2 complex in activating DNA damage checkpoint pathways in response to DSBs in yeast.
• To determine if the Mre11/Rad50/Xrs2 complex is specifically required for checkpoint activation after DSB formation.

Main Methods:

• Studied the phosphorylation and activation of checkpoint kinases Rad53 and Chk1 in response to DSB-inducing agents.
• Assessed cell-cycle delays after inducing DSBs in yeast cells lacking Mre11.
• Examined the phosphorylation of Rad9 after gamma-irradiation in the presence and absence of Mre11.
• Investigated the requirement of Mre11/Rad50/Xrs2 complex components versus other DSB repair proteins (Ku80, Rad51, Rad52) for checkpoint activation.

Main Results:

• The Mre11/Rad50/Xrs2 complex is essential for the phosphorylation and activation of Rad53 and Chk1 checkpoint kinases specifically in response to DSBs.
• Absence of Mre11 leads to defective Rad53 activation and impaired cell-cycle delays following DSB induction.
• Phosphorylation of Rad9, an early checkpoint activation event, is dependent on Mre11 after gamma-irradiation.
• All three components of the Mre11/Rad50/Xrs2 complex are necessary for Rad53 activation, but Ku80, Rad51, or Rad52 are not.

Conclusions:

• The integrity of the Mre11/Rad50/Xrs2 complex is specifically required for the activation of DNA damage checkpoints after the formation of DSBs.
• This finding highlights a specific role for the Mre11/Rad50/Xrs2 complex in sensing and signaling DSBs to initiate cell-cycle arrest.