Fig. (2).

Example of MS/MS for the H3 9-17 peptide trimethylated on K9 acquired from a bottom up MS experiment. All other residues on this peptide are unmodified. Relative intensity of 1.0 denotes the intensity of the most abundant CID fragment ion in the spectrum, namely the b7 ion. Arrows indicate the b and y fragment ion peaks of a given charge state and m/z value that were positively annotated. Hatched marks above and below the peptide sequence also correspond to the b and y fragment ions respectively found in the MS/MS. Abbreviation: pr = propionyl group.