MCF7 were crosslinked with 1% formaldehyde for 10min and then incubated with nuclear extraction buffer (20mM Hepes-KOH ph7.5, 10mM KCl, 1mM EDTA, 0.2% NP40, 1mM DTT and 10% glycerol) to isolate nuclei. The nulei in sonication buffer (20mM Tris-HCl pH8, 150mM NaCl, 2mM EDTA, 0.1% SDS, 1% TritonX-100) was sheared in Misonix Sonicator. The further chromatin immunoprecipitation was implimented with RNAP2 antibody (05-623 Millipore) . The library construction followed the protocol in kit of NEBNext® ChIP-Seq Library Prep Reagent Set (E6200, New England Biolab) with the modfication that single index primer in place of dual primers was used in the final step of PCR amplication. The libraries were indexed with Illumina barcode. Five indexed libraries were finally pooled into one lane and sequenced in Hiseq2500.