Fig. 8.

Spectral count profiles of modified Ser, Thr, and Arg residues. Peptides from equivalent populations of ΔE1B p53 and E p53 isolated in parallel were subjected to nano-UPLC-MS and MS/MS analyses on the Orbitrap Velos platform. Modification profiles were generated from technical triplicate LC-MS runs for each sample by means of spectral counting–based quantification of matched PTMs per residue, as described under “Experimental Procedures.” Shown are the modification profiles for (A) phosphorylation of Ser and Thr residues and (B) mono-, di-, and trimethylation of Arg residues present on both p53 populations.