Format

Send to

Choose Destination
Mol Cell. 2017 Sep 7;67(5):891-898.e4. doi: 10.1016/j.molcel.2017.08.002. Epub 2017 Aug 31.

Single-Molecule Imaging Reveals How Mre11-Rad50-Nbs1 Initiates DNA Break Repair.

Author information

1
Department of Molecular Biosciences, The University of Texas at Austin, Austin, TX 78712, USA; Howard Hughes Medical Institute, The University of Texas at Austin, Austin, TX 78712, USA; Center for Systems and Synthetic Biology, The University of Texas at Austin, Austin, TX 78712, USA.
2
Department of Molecular Biosciences, The University of Texas at Austin, Austin, TX 78712, USA; Center for Systems and Synthetic Biology, The University of Texas at Austin, Austin, TX 78712, USA.
3
Department of Molecular Biosciences, The University of Texas at Austin, Austin, TX 78712, USA; Howard Hughes Medical Institute, The University of Texas at Austin, Austin, TX 78712, USA.
4
Department of Molecular Biosciences, The University of Texas at Austin, Austin, TX 78712, USA; Center for Systems and Synthetic Biology, The University of Texas at Austin, Austin, TX 78712, USA. Electronic address: ifinkelstein@cm.utexas.edu.

Abstract

DNA double-strand break (DSB) repair is essential for maintaining our genomes. Mre11-Rad50-Nbs1 (MRN) and Ku70-Ku80 (Ku) direct distinct DSB repair pathways, but the interplay between these complexes at a DSB remains unclear. Here, we use high-throughput single-molecule microscopy to show that MRN searches for free DNA ends by one-dimensional facilitated diffusion, even on nucleosome-coated DNA. Rad50 binds homoduplex DNA and promotes facilitated diffusion, whereas Mre11 is required for DNA end recognition and nuclease activities. MRN gains access to occluded DNA ends by removing Ku or other DNA adducts via an Mre11-dependent nucleolytic reaction. Next, MRN loads exonuclease 1 (Exo1) onto the free DNA ends to initiate DNA resection. In the presence of replication protein A (RPA), MRN acts as a processivity factor for Exo1, retaining the exonuclease on DNA for long-range resection. Our results provide a mechanism for how MRN promotes homologous recombination on nucleosome-coated DNA.

KEYWORDS:

DNA repair; Ku; MRN; double-strand break; resection; resectosome; single-molecule

PMID:
28867292
PMCID:
PMC5609712
DOI:
10.1016/j.molcel.2017.08.002
[Indexed for MEDLINE]
Free PMC Article

Supplemental Content

Full text links

Icon for Elsevier Science Icon for PubMed Central
Loading ...
Support Center