cells were crosslinked with 1% HCHO, quenched with 0.125 M glycine, washed and resuspended in RIPA buffer (10 mM Tris pH 7.4, 1 mM EDTA, 1% tritonX-100, 0.1% sodium deoxycholate, 0.1% SDS) containing 0.8 M NaCl and sonicated using a water bath sonicator (Diagenode) to obtain DNA of ≈ 300–500 bp. libraries were prepared and sequenced following standard Illumina protocols