Model of ligand-independent signaling by mutant IL-7Rα: role of cysteine, proline, or transmembrane insertions. Hypothetical associations of IL-7Rα (α), γc, Jak1 (J1), Jak3 (J3), disulfide bond resulting from from cysteine insertions (S-S), proline insertions (P), and insertions in the transmembrane region (TM).