Genome-wide analysis of DNA-PK-bound MRN cleavage products supports a sequential model of DSB repair pathway choice

Area of Science:

• Molecular Biology
• DNA Repair Mechanisms
• Cellular Response to DNA Damage

Background:

• The Mre11-Rad50-Nbs1 (MRN) complex is essential for recognizing and processing DNA double-strand breaks (DSBs) during homologous recombination.
• MRN complex's endonucleolytic processing of 5' strands at DSBs necessitates a stably bound protein at the break site.
• DNA-dependent protein kinase (DNA-PK) is hypothesized to fulfill this role in mammalian cells.

Purpose of the Study:

• To investigate the sites of MRN-dependent processing in DNA double-strand break repair.
• To identify the role of DNA-PK in conjunction with the MRN complex during DSB repair.
• To elucidate the sequential binding and processing events involving MRN and DNA-PK at DNA breaks.

Main Methods:

• Identification of CtIP association sites to map MRN-dependent processing.
• Sequencing of DNA fragments bound by DNA-PK, representing products of MRN cleavage.
• Utilizing light-activated Cas9 to induce DSBs for temporal resolution of protein binding dynamics.

Main Results:

• MRN-dependent processing intermediates are generated most efficiently when DNA-PK activity is inhibited, yielding products within 200 bp of the break.
• DNA-PK-bound products exhibit greater dispersal in the absence of kinase inhibition, suggesting a role in processing beyond the immediate break site.
• Temporal resolution experiments show both DNA-PK and Mre11 bind to DNA ends before the release of DNA-PK-bound products.

Conclusions:

• The study supports a sequential model for DNA double-strand break repair.
• Collaborative interactions between homologous (MRN) and non-homologous (DNA-PK) repair complexes are critical for efficient DSB repair.
• DNA-PK plays a significant role in processing DNA ends in concert with the MRN complex.