Peptide pull-down assays were performed as described previously29 (link). In brief, 1 μg of biotinylated histone peptides with different modifications were incubated with 1–2 μg of GST-fused p300 ZZ domain in binding buffer (50 mM Tris-HCl pH 7.5, 300 mM NaCl, 0.1% NP-40, 1 mM PMSF) for overnight with rotation at 4 °C. Streptavidin beads (Amersham) were added to the mixture, and the mixture was incubated for 1 h with rotation at 4 °C. The beads were then washed three times and the bound proteins were analyzed using SDS–PAGE and Western blotting.