Histone isolation and Western blotting

For histone extraction, the protocol is adapted from previous work (Shechter et al. 2007). Briefly, following nuclei isolation, soluble histones were extracted with 0.2 M HCl, followed by TCA/acetone precipitation. For Western blot analysis, protein samples were resolved in SDS-PAGE gels and transferred to PVDF membranes (Millipore). Membranes were blocked with 5% milk in TBST (0.25% Tween 20, 20 mM Tris at pH 8.0, 137 mM NaCl) and incubated with primary antibody overnight at 4°C. After three 5-min washes in TBST, HRP-conjugated secondary antibody was added for 1 h at room temperature. Membranes were visualized by SuperSignal West Pico or Femto (Thermo Fisher Scientific) reagent.