Stable tyrosine phosphorylation of βc and STAT5 requires only a short treatment with LLnL. IL-3–depleted Ba/F₃ cells were treated with LLnL or carrier (DMSO) for 1 or 3 hours as indicated, then stimulated with IL-3 for 0 to 2 hours. βc immune complexes (10⁷ cells) were separated by SDS-PAGE (7% gel), transferred, and immunoblotted with RC20 antibody. Whole-cell extracts were also prepared by lysis in 0.1% SDS and 25-μg samples were separated by SDS-PAGE (6% gel), transferred, and immunoblotted with anti-STAT5b antibody. The position of phospho-βc, pSTAT5, and nonphosphorylated STAT5 is indicated.