STAM contains an SH3 (Src homology 3) motif as well as an immunoreceptor tyrosine-based activation (ITAM) motif, both of which appear to be required for c-Myc induction in response to IL-2 and GM-CSF. STAM associates with JAK3 and JAK2 via its ITAM region, and it is tyrosine phosphorylated by JAK3 and JAK2 after stimulation with IL-2 and GM-CSF, respectively. STAM2, also known as Hbp, is a protein that is highly related to STAM. Similar to STAM, STAM2 functions downstream of JAK kinases and can be phosphorylated in response to cytokines. Due to alternative splicing events, two isoforms of STAM2 exist, namely STAM2A and STAM2B.