Fragments 150-300 bp were size-selected by 2% agarose gel electrophoresis. Recovered DNA was amplified using Phusion DNA polysome (NEB), multiplexing PCR primer 1.0, and one indexed primer. The amplified libraries were purified with Agencourt AMPure XP beads (Beckman Coulter). The libraries were quantitated using the Quant-iT DNA quantitation kit (Invitrogen). The DNA size distribution of the library was measured by an Agilent Bioanalyzer. ChIP-seq library preparation were performed according to the instruction of NEB NEXT-generation library preparation kit. 1 or 2 independent ChIP samples were used for one single ChIP-seq library preparation.