RNAPII ChIP experiments were performed using the ZymoSpin ChIP Kit (Zymo Research) according to instructions. A ChIP-grade anti-RNA-Polymerase II antibody (H-224, sc-9001, Santa Cruz Biotechnology) and as a control normal rabbit IgG (sc-2027, Santa Cruz Biotechnology) were used at concentrations of 2.5 µg/ChIP experiment. The sequences of the primer pairs for the detection of proRBM39 transcript occupancy were described before (Andersen et al. 2013 (link)) (proRBM39#1: fwd: GGGTGGAGAGGAAGTGGAAAAGTG, rev: CCCCTCTCCCCCTACCCCTAAAGA proRBM39#2: fwd: TGTGCCCCGAATTTAATCAGC, rev: TCAGGAAGGGGAACATTTTTGAA and proRBM39#4: fwd: AACAGCTAACTTCTGTTTCTGCT, rev: ACCTGAGAGGCAAAACCACT). Control primers detecting the RNA-Polymerase II occupancy of EGR1 were designed using the Primer3 online tool mentioned above: EGR1-1(fwd): CCGACACCAGCTCTCCAG, EGR1-2(rev): TCAGCAGCATCATCTCCTCC, EGR1-5(fwd): CAGTGGCCTAGTGAGCATGA, EGR1-6(rev): TTGTGGCTCAGGGAAAATGT. The combination EGR1-1/2 amplifies base pairs 239–394 and EGR1-5/6 the nucleotides 744–933 of human EGR1 (NM_001964.2).