Cells were lysed in non-ionic detergents and protease inhibitor cocktail. Cells were digested by Micrococcal nuclease (MNase) at room temperature for 5 minutes and 0.25mM EDTA was used to stop the reaction. Antibodies, H3K27me3 and H3K4me3 were incubated with anti-IgA magnetic beads for 2 hours. Digested chromatin was incubated with magnetic beads alone for 1.5 hours. Digested chromatin was separated from beads and incubated with antibody-bead complex overnight in IP buffer. IPs were washed twice and eluted for 1.5 hours. Histones were digested by Protease for 30min and DNA fragments were purified using Sera Mag magnetic beads in 30% PEG. Illumina sequencing libraries were generated by end repair, 3' A-addition, and Illumina sequencing adaptor ligation.