Characterization of Histone H2A and H2B Variants and Their Post-translational Modifications by Mass Spectrometry*□S

The nucleosome, the fundamental structural unit of chro-matin, contains an octamer of core histones H3, H4, H2A, and H2B. Incorporation of histone variants alters the func-tional properties of chromatin. To understand the global dynamics of chromatin structure and function, analysis of histone variants incorporated into the nucleosome and their covalent modifications is required. Here we report the first global mass spectrometric analysis of histone H2A and H2B variants derived from Jurkat cells. A com-bination of mass spectrometric techniques, HPLC sepa-rations, and enzymatic digestions using endoproteinase Glu-C, endoproteinase Arg-C, and trypsin were used to identify histone H2A and H2B subtypes and their modifi-cations. We identified nine histone H2A and 11 histone H2B subtypes, among them proteins that only had bee