Abstract
Double Strand Breaks (DSBs) are highly toxic lesions, which can be repair by homologous recombination or non-homologous end-joining (NHEJ). Recently has emerged the concept of alternative NHEJ (A-NHEJ) pathway(s).
We used intrachromosomal substrates to monitor NHEJ of DSBs targeted by the meganuclease I-SceI, in living mammalian cells. This substrates allow to characterize A-NHEJ in a chromosomal context; it is highly efficient but extremely inaccurate in the absence of KU. Using this substrate, we have shown that the accuracy of the canonical NHEJ (KU/XRCC4-dependent) pathway is directed by the structure of the extremities rather than the enzymatic machinery itself. The consequences of KU versus XRCC4 depletion, on the choice of the NHEJ pathway, will be discussed.
The above results suggest that the initiation of A-NHEJ is promoted by a nuclease or a helicase to expose single strand DNA allowing annealing of the strands and microhomologies. The involvement of MRE11 (and more generally of the MRN complex) and of CtIP, at the initiation of A-NHEJ will be also discussed here: we conclude that MRE11 is implicated in the two NHEJ pathways but the nuclease activity of MRE11 is only implicated in the A-NHEJ. Other partners are under investigations for the initiation of A-NHEJ.
