Update publication information. To identify putative phosphorylation sites on TCF3 (E47), TCF4, and IRF4, in vitro kinase assays were performed using recombinant MKK6E (a p38α activator) and p38α as kinases, and TCF3(E47), TCF4, or IRF4 proteins as substrates, the phosphorylation sites were analyzed by mass spectrometry (MS).