Briefly, cells were cross-linked with 1% formaldehyde, resuspended in lysis buffer (1% SDS, 10 mM EDTA, and 50 mM Tris-HCl [pH 8.0]) on ice for 3 min, and fragmented by sonication in RIPA ChIP buffer (0.5 mM EGTA, 140 mM NaCl, 10 mM Tris-HCl, pH 7.5, 1% TritonX-100, 0.01% SDS, 1 mM EDTA and protease inhibitor). The samples were then incubated overnight with Protein A/G-beads bound with antibodies [PRMT3 (Abcam, Cambridge, UK), H4R3me2a (Active Motif, Carlsbad, CA), H3 (Cell Signaling)]. After the crosslinking was reversed, immune complexes containing DNA were purified and eluted. The precipitated DNA for sequencing, including H4R3me2a and PRMT3, were constructed into libraries with NEBNext DNA Library Prep Reagent Set for Illumina (NEB) as described by the manufacturer.