Cells were processed by Active Motif via a standard ChIPseq protocol to enrich for RNAPII bound regions of DNA.  Replicate RNA Pol II ChIP reactions were performed using 25 μg of primary MEF, 6F, and DDRR chromatin and 4 μg of Abflex RNAPII antibody (Active Motif, cat # 91151). Libraries were generated via standard Illumina protocols (using NextSeq 500) and sequenced to generate 30M reads per sample.