Mass spectrometric characterization of human histone H3: A bird's eye view

The modification of H3 in asynchronous HeLa cells was profiled using Top Down Mass Spectrometry. A broad distribution of species differing by 14 Da and containing less than 3% unmodified protein was observed for all three variants. Species of up to +168 Da were observed for H3.1, and fragmentation of all species by Electron Capture Dissociation (ECD) revealed ∼5% methylation of K4 and ∼50% dimethylation of K9. K14 and K23 were major sites of acetylation. H3.3 was slightly hypermodified with the apex of the distribution shifted by ∼+14 Da compared to H3.1. H3.1 (50% and 15%) from colchicine-treated cells was monophosphorylated and diphosphorylated, respectively, with equivalent modification of S10 and S28.