Carries out a dual function: signal transduction and activation of transcription. Involved in IL12 signaling. Forms a homodimer or a heterodimer with a related family member. Interacts with ARL2BP (By similarity). The SH2 domain interacts, in vitro, with IL12RB2 via a short cytoplasmic domain. Translocated into the nucleus in response to phosphorylation. Tyrosine phosphorylated. Serine phosphorylation is also required for maximal transcriptional activity (By similarity). Disease susceptibility is associated with variants affecting the gene represented in this entry. Disease susceptibility is associated with variants affecting the gene represented in this entry. Belongs to the transcription factor STAT family.