JAK2^ex13InDel activates ERK1/2 and STAT5 signaling in Ba/F3 cells in the absence of IL-3. (A) Ba/F3 cells cultured in the presence of IL-3 displayed activation of STAT5 and ERK1/2. In the absence of IL-3, STAT5 and ERK1/2 activation was maintained only by JAK2^ex13InDel-expressing cells. Additional proteins did not demonstrate differential JAK2^ex13InDel activation in the absence of IL-3. (B) In the absence of IL-3, JAK2 phosphorylation was detectable only in JAK2^ex13InDel-expressing cells. IB, immunoblot; IP, immunoprecipitate.