(A) Mass spectrometry (MS/MS) spectrum of the N-terminal H2A.Z-2 peptide, AGGKAGKDSGKAKAKAVSR. The peptide is modified with three acetyl groups on lysines 4, 7, and 11. (B) MS/MS spectrum of the triply-acetylated N-terminal peptide, AGGKAGKDSGKTKTKAVSR, of H2A.Z-1. The acetyl groups were again identified on lysines 4, 7, and 11. The precursor ions selected for dissociation were the [M+2H]+2 ions, and are m/z 1041.1 (A) and m/z 1071.1 (B), respectively. The amino acid sequences are shown above the spectra, and the masses above and below the sequences correspond to the theoretical b- and y-type product ions. The masses provided are the monoisotopic, nominal masses of the product ions. The observed, singly-protonated b- and y-type ions are underlined and are assigned to their corresponding m/z peaks in the spectra. The observed, doubly-protonated ions are denoted with asterisks. The acetylated lysines (K4, K7, and K11) are indicated with 'ac'. The unacetylated amino groups were derivatized with propionic anhydride and are denoted with 'pr'. (C) Selected ion chromatograms (SICs) for the N-terminal peptides of H2A.Z-2 and H2A.Z-1. The theoretical m/z values of the [M+2H]+2 and [M+3H]+3 ions for each peptide were used to generate the SICs and these values are adjacent to each chromatogram. Note that the retention time decreases with increasing number of acetyl groups due to the loss of propionylated lysine. The ion count intensities for each SIC are located on the y-axis and are provided on the left adjacent to each chromatogram.