Detection of a proteolytic C-terminal STAT5 fragment in FDC-P1 cells. Nuclear extracts of unstimulated (−) or IL-3–stimulated (+) FDC-P1 and FDC-P1(M) cells were analyzed by Western blotting using a C-terminal anti-STAT5 antibody (C-17). The full-length STAT5α protein is indicated on the right. The proteolytic C-terminal fragment of STAT5 is indicated on the left.