library_construction_protocol: Cells were dissociated by Trypsin EDTA and cross-linked with 1% formaldehyde for 10 minutes at room temperature (RT) and quenched with 125mM glycine for 5 minutes at RT. Cells were rinsed with PBS and filtered.  1,000,000 cells were lysed in 100μl of Sonication Buffer for 15 min on ice, and sonicated using the Covaris machine to obtain DNA fragment the size of which distributes between 150bp and 500bp. The supernatant was transferred to a new tube, diluted with Equilibration Buffer. Chromatin solutions were incubated over-night at 4°C with 5μg of anti-H3K27ac (abcam, ab4729, PRID: AB_2118291) antibodies. The next day, 20μl of protein G coupled to magnetic beads were added and the incubation was continued for 2 hours at 4°C. The beads were then washed five times with RIPA Buffer, twice with High-Salt RIPA Buffer, twice with LiCl Buffer, and twice with 10mM Tris HCl pH8. DNA was eluted from the beads with 60μl Elution Buffer at 65°C for 5hours. DNA was purified with SPRI AMPure XP beads and eluted in 25μl 10mM Tris HCl pH8. Libraries were prepared according to NEBNext Ultra DNA Library Prep Kit for Illumina (NEB, E7370).