Fig. 4.

Representative MS/MS spectra of ΔE1B p53. Peptides prepared from p53 isolates were subjected to reversed-phase nano-LC-MS and MS/MS on a UPLC-Orbitrap Velos platform as described under “Experimental Procedures.” Shown are representative examples of tandem mass spectra displaying their PTM-bearing peptide fragment ion assignments. Prominent fragment ions are labeled with their empirical m/z values and b- and y-ion designations or annotations indicating neutral losses from precursor species. The peptide sequences are displayed above the spectra, with all of the fragment ions matched in the spectra indicated by flags. Modified residues are color-coded by PTM in the following manner: phosphorylation, red; acetylation, green; ubiquitinylation, purple; monomethylation, navy; dimethylation, cerulean; trimethylation, turquoise; oxidation, tan; and carbamidomethylation, orange.