Cells were fixed in 1% formaldehyde for 10 minutes at room temperature and then treated with 125 mM Glycine for 5 minutes to stop crosslinking. Crosslinked cells were then washed with cold PBS and scraped to harvest. ChIP and library construction was performed as described in Reddy et al, Genome Research, 2009. ChIP and library construction was performed as described in Reddy et al, Genome Research, 2009. The following antibodies were used: HA (Biolegend 16B12), H3K27ac (Active Motif pAb Cat #39133) and RNAPII (abcam ab5408)