Cells were fixed with 1% formaldehyde for 15 minutes (Brd4 ChIP) or 5 minutes (H3K27ac ChIP). DNA was sonicated to an average length of 200 - 500 bp. IP and Input DNA was reverse crosslinked and purified for library preparation. Illumina sequencing libraries were prepared from the ChIP and Input DNAs by the standard consecutive enzymatic steps of end-polishing, dA-addition, and adaptor ligation.