The common cytokine receptor γ chain is used by IL-2, IL-4, IL-7, IL-9, IL-15 and IL-21. The IL-2R and IL-15R have a second (β chain) subunit in common as well, but have unique α subunits. These two cytokine receptors use a common signaling pathway that involves JAK1, JAK3 and STAT5. The signaling involves the phosphorylation of STAT5 that results in the dissociation of STAT5 from the receptor and the subsequent dimerization of STAT5. The dimers then translocate to the nucleus and promote transcription of target genes.