AML cells (10 million) were treated with 1% formaldehyde for 10 minutes with rotation. The crosslinking reaction was quenched with 2.5 M Glycine for 5 minutes. Chromatin lysates were clarified from ultra-sonicated nuclei and histone-DNA complexes or BRD4-containing complexes were isolated with H3K27Ac or BRD4 antibody, respectively. Following ChIP washes, the immunoprecipitated DNA fragments were treated with mutant Tn5 transposase for 10 minutes at 37°C to attach sequencing adapters to the DNA. Tagmented DNA was eluted and formaldehyde-induced crosslinks were reversed. Tagmented, eluted DNA was purified over a column and utilized for library preparation. For ATAC-Seq analysis, isolated nuclei were treated with Tn5 transposase in tagmentation buffer at 37°C for 30 minutes. Tagmented, eluted DNA was purified over a column and utilized for library preparation. Libraries were prepared according to Illumina's instructions accompanying the Nextera DNA Library Prep Kit (Cat. No. FC-121-1030). After adapter ligation, DNA was PCR amplified with Illumina universal primer for 15 cycles (12 cycles for ATAC-Seq) and library fragments of ~250 bp (insert plus adaptor and PCR primer sequences) were isolated utilizing AMP-XP beads. For ATAC-Seq, fragments larger than 200 bp were isolated utilizing AMP-XP beads. The purified DNA was captured on an Illumina NExt-Seq 500 flow cell for cluster generation. Libraries were sequenced following the manufacturer's protocols.