ATACseq libraries were generated from ~75,000 mESC nuclei following the Omni ATAC protocol114 with a modified transposition reaction: TAPS-DMF buffer (50 mM TAPS-NaOH, pH 8.5, 25 mM MgCl2, 50% DMF), 0.1 % Tween-20, 0.1% Digitonin, in PBS. 3 uL of the a Tn5 mix (5.6 g Tn5 and 0.143 volume of 100uM adapter mix) were added to the transposition reaction mix. Libraries were prepared as described in the Omni ATAC protocol. The final library was sequenced with an Illumina NextSeq 500 machine, according to manufacturer's instructions, using paired-end 75 bp reads (150 cycles).