A 100-kilodalton protein is associated with the murine interleukin 2 receptor: Biochemical evidence that p100 is distinct from the α and β chains

Two proteins that specifically bind the T-cell growth factor interleukin 2 (IL-2) have been identified previously on the surface of T cells; these proteins have been designated IL-2Rα and IL-2Rβ for the α and β chains of the IL-2 receptor (IL-2R). The association of these independent binding proteins with each other on the surface of activated T cells correlates with the generation of high-affinity binding sites. These high-affinity sites transduce the major mitogenic signal of IL-2, yet the mechanisms of association of the α and β chains with each other as well as signal transduction in response to IL-2 are unknown. Cotransfection experiments of cDNAs encoding the α and β chains in T cells and fibroblasts have suggested functional requirements for other T cell-specific factor(s). The authors now provide biochemical evidence for a distinct 100-kDa protein that interacts with the α or β chains, or both, on the surface of the IL-2-dependent cell line CTLL-2 as well as activated murine splenocytes. This same 100-kDa protein is capable of being chemically cross-linked to 125I-labeled IL-2