Cells were treated and harvested for ChIP-seq as described previously (Schmidt et al, 2009, http://www.ncbi.nlm.nih.gov/pubmed/19275939). The anti-ER (sc-543) from Santa Cruz Biotechnologies was used as the antibody. Chromatin was extracted from the cells and the protein of interest, along with the DNA attached, was immunoprecipitated using the antibody attached to Dynal beads (Dynabeads® Protein A 10001D, Life Technologies). The proteins were then removed from the DNA by reverse crosslinking overnight and the DNA purified and amplified before being sequenced. DNA libraries were generated from ChIP output DNA by adaptor ligation, gel purification, and cycles of PCR as described by Illumina.