A third subunit, the γ chain, of the human interleukin-2 receptor (IL-2R) was identified, and a complementary DNA clone encoding this member of the cytokine receptor family was isolated. The γ chain is necessary for the formation of the high- and intermediate-affinity receptors, which consist of αβγ heterotrimers and βγ heterodimers, respectively. The IL-2R on murine fibroblastoid cells can be internalized after binding IL-2 only if the γ chain is present; α and β are insufficient for internalization. Thus, the γ chain is an indispensable component of the functional IL-2R.
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