This Motif Logo was generated from a PhosphoScan<sup>®</sup> LC-MS/MS experiment using 1111 nonredundant tryptic peptides derived from Jurkat cells treated with Calyculin A #9902 and pervanadate and immunoprecipitated using PTMScan<sup>®</sup> Phospho-ATM/ATR Substrate Motif [pSQ] Immunoaffinity Beads. The PhosphoSitePlus<sup>®</sup> logo reflects the relative prevalence of an amino acid in each position relative to the phospho-serine background in the human proteome. Residues represented above the x-axis are enriched relative to their expected frequency in this background. For more information on motif analysis using PSP, please visit www.phosphosite.org.