Histone modification binding assay and peptide pull-down assay

These experiments were performed as previously described (Gong et al. 2015). For the histone modification binding assay, a modified histone peptide array (Active Motif) was blocked with 5% (v/v) nonfat milk in TNT buffer (50 mM Tris-HCl, pH 7.5, 150 mM NaCl, 0.05% [v/v] Tween-20) and then incubated with the indicated recombinant proteins at 4°C for 1 h. The histone peptide array was washed three times with TNT buffer and detected with HRP conjugated antibody. To validate the results of the histone peptide array, peptide pulldown assays were carried out using PCAF-expressing cell extracts. Biotinylated H4 peptides were incubated with PCAF-expressing HEK-293 cell extracts at 4°C for 1 h. Samples were pulled down with streptavidin Dynabeads (Invitrogen), and bound proteins were detected by western blotting using the indicated antibodies.