library_construction_protocol: Cells were fixed with 1% formaldehyde for 10 minutes and quenched with glycine at room temperature. Crosslinked cells were lysed with 400 μL NPB buffer (5% BSA, 1mM DTT, 0.2% IGEPAL, Roche Complete Protease Inhibitor) on ice for 15 min to isolate the nuclei. For tagmentation, the nuclei were resuspended in 50 μL 2X TB buffer (66mM Tris-AC pH 7.8, 132mM KCl-AC, 20mM Mg-AC, 32% DMF), 45 μL molecular biology grade water and 5 μL assembled Tn5 transposase, and rotated at 37°C for 1 h. Then the nuclei were treated by MseI or CviQI for the first digestion, followed by in situ ligation with T4 DNA ligase. The second restriction enzyme digestion was performed using NlaIII, followed by the circularization and PCR amplification.