FIGURE 1.

Identification of Ser-193 as a novel proline-flanked phosphorylation site in human Stat5b. YT cells were stimulated without (−) or with (+) IL-2 for 15 min, and Stat5b proteins were immunoprecipitated (IP) from soluble cell lysates with α-Stat5b antibodies. Two sets of immunoprecipitations were separated by SDS-PAGE. One set was Coomassie Blue-stained (A), and the other was Western blotted (WB) (B) with α-phospho-Tyr (α-pY), α-phospho-Ser (pS726/731), or α-Stat5b antibodies. HC, heavy chain; LC, light chain. C, tandem mass spectra of a monophosphorylated peptide showing site localization of Ser-193, as indicated by asterisks. D, amino acid sequence alignment of the region surrounding Ser-193 (asterisk) from each human Stat protein using the ClustalW program (progressive alignment) (31). E, domain architecture of human Stat5 with known and newly identified (asterisk) serine and tyrosine phosphorylation sites. Numbers indicate amino acid residues of human Stat5 (a/b).