RAD51_OHT_s
DIvA (AsiSI-ER-U20S) cells were cultured in Dulbecco's modified Eagle's medium (DMEM) supplemented with antibiotics, 10% FCS (Invitrogen) at 37°C under a humidified atmosphere with 5% CO2. For AsiSI-dependent DSB induction, cells were treated with 300 nM 4OHT (Sigma; H7904) for 24h. Formaldehyde was added to the culture medium at a final concentration of 1% and crosslinking was allowed to proceed for 15 min at room temperature. Reaction was stopped by adding glycine (0.125M final concentration) and incubation for 5 minutes at room temperature. Cells were washed twice with PBS and harvested by scraping. Cell lysis was performed by incubation in cell lysis buffer (5 mM Pipes pH 8, 85 mM KCl, 0.5% IGEPAL® CA-630) followed by Dounce homogenization. Nuclei were harvested by centrifugation and incubated in nuclear lysis buffer: (50 mM Tris pH 8.1, 10 mM EDTA, 1% SDS) and sonicated 10 times for 10 s at a power setting of 5 and 50% duty cycle (Branson Sonifier 250). Samples were diluted 10 times in ChIP dilution buffer (16.7 mM Tris pH 8.1, 167 mM NaCl, 1.2 mM EDTA, 1.1% Triton X‐100, 0.01% SDS) and precleared using a mixture of protein A-agarose (Pierce) and protein G-sepharose (Sigma) previously blocked with BSA (Sigma). Precleared samples (200 μg) were incubated overnight at 4°C with anti-RAD51 (Santa Cruz, SC-8349). Immune complexes were recovered by incubation with blocked protein A/protein G beads for 2 h at 4°C on a rotating wheel. Beads were washed once in dialysis buffer (50 mM Tris pH 8, 2 mM EDTA, 0.2% Sarkosyl), five times in wash buffer (100 mM Tris pH 8.8, 500 mM LiCl, 1%  IGEPAL® CA-630, 1% NaDoc) and twice with TE (10mM Tris-HCl, pH 8, 1mM EDTA). Beads were resuspended in TE supplemented with 50µg/ml DNase-free RNase A (Abcam) and incubated for 30 minutes at 37°C. SDS (final concentration 0.5%) was added and crosslink was reversed by overnight incubation at 70°C. Following a 2 hours treatment with 200 µg/ml proteinase K (Roche) at 45°C, DNA was purified by phenol/chloroform extraction and recovered by ethanol precipitation in presence of 5 µg glycogen (Invitrogen). DNA pellet was resuspended in water. Prior to next-generation sequencing library preparation, samples from multiples ChIP experiments were pooled and sonicated for 5 cycles (30 seconds on, 30 seconds off, high setting) on a Bioruptor (Diagenode) then concentrated with a vacuum concentrator (Eppendorf).  Library preparation was performed at EMBL Genomics core facilities (Heidelberg, Germany) using NEBNext ChIP-Seq Library Prep kit (New England Biolabs).