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 approximately 5% 
methylation of K4 and approximately 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 approximately +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.