Nuclei were isolated from the mouse brain. Proteins were extracted with addition of Bensonase and cleaned up by acetone precipitation. Proteis were resuspended in 50 mM ammonium bicarbonate and PPS Silent Surfactant. Samples were sonicated on ice to improve the solubility of proteins, then alkylated with IAA and digested with trypsin. Peptides were analyzed by LC-MS/MS using the UltiMate 3000RS nano-System coupled with microTOF_QII.