Updated FTP location. Dynabeads Protein A (Invitrogen) were prepared according to the manufacturer’s protocol. The nuclear lysates were incubated with DynaBeads Protein A coated with appropriate antibodies for 4 hours at 4°C. After washing the beads for 5 times in wash buffer (PBST) to remove non-specific proteins, the beads-bound proteins were analysed by mass spectrometry.