We have developed substrates to analyse end-joining in an intra-chromosomal context. The substrates we have developed allowed us to identify and characterize the alternative end-joining pathway (A-EJ), in an intrachromosomal context, in living cells. A-EJ is initiated by single-stranded DNA resection (like HR). The choice of the DSB repair system is therefore two levels: 1- NHEJ vs. Resection; 2-A-EJ vs. RH. Our project plans to analyse the impact of HR proteins, Brca2 and Rad51, in the choice A-EJ vs HR. We are analysing the mechanisms controlling the correct choice of DSB repair system. Finally, we analyse the impact of RAD51 and RAD52 on these different processes.