IKK phosphosite identification in EDC4 by mass spectrometry (see
Table EV2 for MS data). Endogenous IKK purified from unstimulated or TNFα‐treated (10 ng/ml, 15 min) U2‐OS cells by immunoprecipitation of IKKγ was used in a cold KA with recombinant EDC4 sub‐regions, followed by MS analysis. Top, MS spectrum for phospho‐serine 583. Bottom, MS spectrum for phospho‐serine 855.