We previously reported a molecule, p64, which was tentatively named the γ chain, coprecipitable with the β chain of human interleukin-2 receptor (IL-2R). The present study demonstrated that the γ chain, as well as the β chain expressed on IL-2-responsive cells, is phosphorylated on tyrosine residues in an IL-2-dependent manner in vivo and in vitro. The in vivo tyrosine phosphorylation of both chains was similarly induced within 1 min after IL-2 stimulation, and their in vitro tyrosine phosphorylation with the anti-IL-2Rβ antibody-directed immunocomplex was also increased by treatment of cells with IL-2. These results suggest that a tyrosine kinase is associated with the βγ subunit complex, of which activation by IL-2 may result in transduction of intracellular signals.
