The MRN complex and the cellular response to DNA double-strand breaks

The MRN complex and the cellular response to DNA double-strand breaks The Mre11/Rad50/Nbs1 (MRN) complex is a multisubunit nuclease that plays a crucial role in DNA double-strand break (DSB) repair and ATM (Ataxia-Telangiectasia mutated)-mediated checkpoint signaling. The first part of this thesis addresses the controversy over MRN complex involvement in the non-homologous end-joining (NHEJ) DSB repair pathway by the use of a plasmid DSB repair assay in Xenopus laevis cell-free extracts. Mre11-depleted extracts are able to support efficient NHEJ repair of DSBs, regardless of the end-structure. Mre11-depletion does not alter the kinetics of end-joining or the type and frequency of junctions found in repaired products. Finally, Ku70-independent end-joining events are not affected by Mre11 loss. Our data demonstrate that the MRN complex is not required for efficient and accurate NHEJ-mediated repair of DSBs in this vertebrate system. In the second part, I discuss the techniques, molecular tools and preliminary results of the characterization of the molecular mechanisms underlying the involvement of the MRN-ATM pathway in the maintenance of genome integrity during DNA replication.