Permeabilized ES and sperm nuclei were treated with 10 Units/10^6cells and 1 Unit/10^8cells of micrococcal nuclease (Worthington), respectively, for 5 min @ 37°C. Reaction was stopped with the addition of 10 mM EGTA on ice. For ES cells, nuclei were incubated for 4 hrs at 4°C with rotation, pelleted at 5000g for 5 min, and separated into supernatant and pellet (spun) or were treated the same without centrifugation and separation (unspun). After MNase digestion of sperm nuclei, digestion was centrifuged for 5000g for 5 min. To characterize the entire range of MNase digestion products, we generated paired-end libraries of DNA fragments from both ES and sperm digestions and performed sequencing using Illumina HiSeq technology. Libraries were prepared as described in PMID: 22025700.