Nuclei were isolated by lysing cells with 0.1% NP-40. ATAC-seq libraries were generated as published (Buenorostro et al. 2015). Briefly, nuclei were treated with tagmentation enzyme from Nextera Library Prep Kit, and DNA was purified on a Qiagen MinElute column. Libraries were amplified and sequencing adaptors were added by PCR. HiSeq 2500 in Rapid Mode