Ten million cells were used for the ChIP and precipitated using 10 micrograms of antibody against Ser-5-Phosphoryalted RNA polymerase II (Abcam, ab5131 ) and against Ser-2-Phosphoryalted RNA polymerase II (Active Motif, clone 3E10) Libraries were generated as described before, including end-repair, A-tailing, adapter (Illumina Truseq system) ligation and PCR amplification.