Protein purification and in vitro methylation assay

His-tagged CCT7, TFG, YBX1, CKMT1B, hnRNPK, hnRNPA2B1, and ΔNp63α were expressed in BL21 (DE3) bacterial cells (Stratagene) and purified by using Ni-NTA Resin (Thermofisher).

HA-tagged PRMT7 was expressed in HEK293T and lysed in a lysis buffer containing 50 mM Tris-HCl (pH 7.4), 420 mM NaCl, 1 mM EDTA, and 1% Triton X-100 supplemented with complete protease inhibitor cocktail followed by affinity purification by using anti-Flag M2 agarose and washed extensively with washing buffer containing 50 mM Tris-HCl, pH 7.4, 420 mM NaCl, 1 mM EDTA, 1% Triton X-100 before elution with 3 × Flag peptides (Sigma).

In vitro methylation assay was performed in methylation buffer (50 mM Tris-HCl, pH 8.0, 20 mM KCl, 5 mM DTT, 4 mM EDTA) in the presence of methionine at 37 °C for 1 h. The reaction was stopped by adding SDS sample buffer followed by SDS-PAGE gel and immunoblotting.