Tetrameric Ctp1 coordinates DNA binding and DNA bridging in DNA double-strand-break repair

Area of Science:

• Molecular Biology
• Genetics
• Biochemistry

Background:

• Ctp1 (CtIP/Sae2) is a key collaborator in DNA double-strand break (DSB) repair pathways, working alongside the Mre11-Rad50-Nbs1 complex.
• Despite its importance, the precise functions and structural basis of Ctp1's role in DSB repair remain incompletely understood.

Purpose of the Study:

• To elucidate the structural architecture and DNA-binding/bridging activities of the tetrameric Ctp1 protein from Schizosaccharomyces pombe.
• To determine the functional significance of Ctp1's structural domains in DNA repair processes.

Main Methods:

• Structural analysis of the Ctp1 tetramer using biophysical techniques.
• In vitro assays to assess DNA-binding and DNA-bridging activities.
• Genetic analysis in S. pombe to evaluate the role of Ctp1 domains in DSB repair.

Main Results:

• The tetrameric Ctp1 protein possesses multivalent DNA-binding and DNA-bridging capabilities.
• Ctp1 architecture comprises an N-terminal tetrameric helical dimer-of-dimers (THDD) domain, a central intrinsically disordered region (IDR), and C-terminal DNA-interaction motifs (RHR).
• The THDD, IDR, and RHR are all necessary for Ctp1's DNA-bridging activity, while the THDD and RHR are essential for efficient DSB repair in vivo.

Conclusions:

• Ctp1 plays non-nucleolytic roles in binding and coordinating DNA repair intermediates during DSB repair.
• Truncating mutations affecting human CtIP DNA binding may underlie Seckel and Jawad syndromes, highlighting the clinical relevance of these findings.