Lysates were clarified from sonicated nuclei and histone-DNA complexes were isolated with corresponding anti-body Libraries were prepared according to QIAGEN's instructions accompanying the QIAseq Ultralow Input Library Kit (Part# 180492). In the adaptor ligation step, the original adaptor reagent was diluted to 100 times. After adapter ligation DNA was PCR amplified with Illumina primers for 13~16 cycles and library fragments of ~300 bp (insert plus adaptor and PCR primer sequences) were purified with AMPure XP beads(Beckman Coulter). The purified DNA was captured on an Illumina flow cell for cluster generation. Libraries were sequenced on the Illumina HiSeq following the manufacturer's protocols.