Isolated cells were lysed with 50 µL cold lysis buffer (10 mM Tris-HCl, pH 7.4, 10 mM NaCl, 3 mM MgCl2, 0.1% NP-40; all components purchased from Sigma) in a centrifuge at 500 x g for 15 minutes at 4°C. Pelleted nuclei were resuspended in 50 µL tagmentation reaction mix (25 µL Nextera TD Buffer, 2.5 µL Nextera TD Enzyme, and 22.5 µL H2O, all from the Nextera DNA Sample Preparation Kit (Illumina). Immediately after Tn5 tagmentation, DNA samples were purified and indexed using NEBNext® High-Fidelity 2x PCR Master Mix (New England Biolabs) with a customized Nextera PCR primer pair, according to the following program: 72°C for 5 minutes; 98°C for 30 seconds; 11 cycles of 98°C for 10 seconds, 63°C for 30 seconds, and 72°C for 1 minute; and hold at 4°C. All DNA libraries that exhibited a nucleosome pattern in the BioAnalyzer 2100 Assay passed the pre-sequencing QC process and were pooled for high-throughput sequencing.