design: 1530 million cells were crosslinked (10 min, 20C) in 1% paraformaldehyde (Electron Microscopy Science). Nuclei were isolated, and chromatin was prepared, fragmented, and collected using the ChIP-It High Sensitivity kit (Active Motif). Immunoprecipitation was performed on aliquots of 25 g chromatin using antisera targeting acetylated lysine 27 of histone H3 (Abcam; ab4729), the H3K27ac ChIP-seq grade Antibody (Diagenode, C15210016), or IgG controls (Active Motif; 53017). DNA was purified using a DNA clean-up kit (Zymo Research) and used as template for high throughput DNA sequencing on an Illumina HiSeq 2000 platform.