Structure of the functional interleukin-2 receptor: Evidence for the association of human p55 and murine p75 molecules in a mouse T cell line

The structural basis of the high affinity interleukin-2 receptorwhich was previously reconstituted in a cultured murine T cellline, EL4 by expressing either wild-type Tac antigen complementaryDNA (cDNA) or a chimeric cDNA was characterized. The chimericcDNA encodes a membrane portion whose extracellular portionconsists of that of Tac antigen whereas transmembrane and cytoplasmicportions consists of those the human insulin beta chain. TheTac antigen/anti-Tac antibody complex was treated by chemicalcrosslinking reagents, purified by goat anti-mouse immunoglobulin(lg), and was analysed by SDS–PAGE. We here demonstrated the presence in mouse EL4 transfectantsof a novel membrane protein which is closely associated withthe products of transfected cDNAs in the absence of interleukln-2.The protein is 75 kDa in size and is detected in cells whichexpress high affinity interieukln-2 receptor but not in cellswhich only express low affinity interleukin-2 receptor. Thetransmembrane region and the cytoplasmic region of Tac antigenis not necessary for the formation of the complex consistingof Tac antigen and 75 kDa molecule, indicating that a murine75 kDa molecule associates with Tac antigen extra-cellularly.