Structure of the Rad50 DNA double‐strand break repair protein in complex with DNA

The Mre11–Rad50 nuclease– ATP ase is an evolutionarily conserved multifunctional DNA double‐strand break ( DSB ) repair factor. Mre11–Rad50's mechanism in the processing, tethering, and signaling of DSB s is unclear, in part because we lack a structural framework for its interaction with DNA in different functional states. We determined the crystal structure of T hermotoga maritima Rad50 NBD (nucleotide‐binding domain) in complex with Mre11 HLH (helix‐loop‐helix domain), AMPPNP , and double‐stranded DNA . DNA binds between both coiled‐coil domains of the Rad50 dimer with main interactions to a strand‐loop‐helix motif on the NBD . Our analysis suggests that this motif on Rad50 does not directly recognize DNA ends and binds internal sites on DNA . Functional studies reveal that DNA binding to Rad50 is not critical for DNA double‐strand break repair but is important for telomere maintenance. In summary, we provide a structural framework for DNA binding to Rad50 in the ATP ‐bound state.