Signal transducer and activator of transcription 4 (STAT4) is activated through interaction with tyrosine-800 of Interleukin-12 receptor beta 2 subunit (IL12RB2). Based on experiments with murine-specific peptides, STAT4 activation depends on interaction with the peptide sequence pYLPSNID, where pY represents phosphotyrosine. STAT1 and STAT3 are not activated directly through the Interleukin-12 heterodimeric receptor (Naeger et al. 1999).
As the pattern of phosphorylations required for this event is unclear, it is represented here as a black box event.