Following stimulation by IL2, the IL2R beta chain become phosphorylated on multiple tyrosine residues. These phosphotyrosine residues recruit position-specific signaling or adaptor proteins, leading to the activation of downstream signaling pathways. Although multiple kinases are involved in the phosphorylation of IL-2R beta, JAK1-dependent phosphorylation of tyrosines 338, 392 and 510 is known to be involved in STAT protein binding (Gaffen et al. 1996). Phospho-tyrosine 338 has also been shown to participate in recruitment and subsequent phosphorylation of the adaptor Shc (Friedmann et al. 1996). N.B. Numbering in the literature is based on the mature peptide, with the 26 residue signal peptide removed. Positions given in this reaction refer to the canonical Uniprot sequence, e.g. 338 is equivalent to 364 of the canonical sequence P14784.