Both in yeast and mammals, the scaffold protein SLX4/FANCP has been implicated in late steps of homologous recombination DNA repair, delivering the structure specific nucleases MUS81, SLX1 and XPF/RAD1 onto DNA repair intermediates (such as joint molecules and 3\u2019 non homologous DNA flap). Working with the model organism S. cerevisiae, we showed that Slx4 competes with the 53BP1-ortholog Rad9 for DSB end binding, favoring DNA end resection and homologous recombination repair. To investigate a possible conservation of the pathway, we exploited the AsiSI restriction enzyme and Cas9-based systems to study SLX4 role in controlling DSB resection in U2OS human osteosarcoma cells and FANCP patient derived fibroblasts. We also analyzed homologous recombination DNA repair through standard GFP reporter cassette assays and immunofluorescence foci of specific factors. The obtained results indicate that down regulation of SLX4/FANCP limits DSB resection and repair, supporting an important conserved SLX4/FANCP role in early steps of homologous recombination DNA repair, independently of the nucleases MUS81 and XPF
