Histone peptides and post-translational modifications (PTMs) detected in mouse sperm. A) Proportion of detected histone peptides. The number of different peptides identified for each histone type, and sequence coverage (%) observed. The percentage of peptides with and without PTM is indicated. B) 27 PTMs identified on histones H1, H2B, H3 and H4. PTMs are indicated by A for acetylation, Me1, Me2 and Me3 for mono-, di- and trimethylation, and P for phosphorylation. Residues are numbered starting with the first residue after the cleaved methionine according to histone field standard. * indicates that the acetylation site could not be assigned to a single residue, (that is, N-terminus or serine acetylation).