ChIP'd DNA was extracted accordingly in previous publication (Byun et al, ELL faciliates RNA polymerase II pause site entry and release. Nature Communications 3, 633 2012. ChIP-Seq samples were sequenced on GAIIx with 36bp length using Illumina TruSeq v3 Chemistry, Allthe samples have good quality with over 93% of bases having Q30 or above. Library complexity is measured by uniquely aligned reads using picard's markduplicate utility.