Chromatin immunoprecipitation assay

Chromatin immunoprecipitation assays were performed as described previously (11). In brief, 10⁶ A2780 and A2780/CP70 cells were plated. Twenty-four hours later, cells were fixed and chromatin preps were immunoprecipitated with ATR (Cell Signaling Technology, Danvers, MA) and CHK1 (Santa Cruz Biotechnology, Dallas, TX) antibodies using the SimpleChip Enzymatic Chromatin IP Kit (Cell Signaling Technology, Danvers, MA). Samples were amplified using a ViiA 7 Real-Time PCR system (Thermo Fisher Scientific, Waltham, MA) using primers shown in the Supplementary Table 3. A 321-bp region was amplified with the ATR1 and CHK1 primers and a 285-bp product was amplified with the ATR2 primers (−147 to +158 from the TSS).