Protamine peptides and post-translational modifications (PTMs) detected in mouse sperm. A) Proportion of detected PRM1 and PRM2 peptides. Number of different peptides identified for each protamine, and percentage of peptides with and without PTM are indicated. B) A total of 11 PTMs newly identified on protamines PRM1 and PRM2. PTMs are indicated by A for acetylation, Me for methylation and P for phosphorylation. Residues are numbered starting with the first residue after the cleaved methionine according to histone field standard. The protamine sequence coverage is color coded and indicates the number of peptides that covered a given residue. The cleavage site of the PRM2 precursor at R44 is indicated in the sequence.