To crosslink chromatin, 37% formaldehyde (Sigma-Aldrich) was added directly to the media and allowed to incubate at room temperature for 10 minutes. Glycine was added at a final concentration of 125 mM to stop crosslinking, and cells were washed with cold 1X PBS. Plates were scraped in Farnham lysis buffer with 1X protease inhibitor (Thermo Fisher). Chromatin was sonicated using an Active Motif EpiShear Probe Sonicator with 6 cycles of 30 s, at 40% amplitude, with 30 s of rest. ChIP was performed as previously described (Reddy et al., 2009) using anti-ER (Santa Cruz HC-20) and anti-H3K27ac (Active Motif 39133) antibodies. ChIP and library construction was performed as described in Reddy et al, Genome Research, 2009. The following antibodies were used: H3K27ac (Active Motif pAb Cat #39133) and ER (Santa Cruz HC-20) Libraries were sequenced on an Illumina HiSeq 2500 as single-end 50 basepair reads