STATs (signal transducers and activators of transcription) are a family of latent cytoplasmic proteins that are activated when cells encounter various extracellular polypeptides, such as interferons and interleukines. STATs are involved in many pathways that regulate cellular functions in the lympho-hematopoietic system. The STAT family has seven members: STAT1, 2, 3, 4, 5A, 5B and 6. STAT1 forms heterodimers with STAT2 and 3; STAT4 and 5 only form homodimers. Tyrosine phosphorylation around residue 700 is essential for the dimerization of STATs and the concomitant nuclear translocation of the dimer. STAT dimers and heterodimers, but not monomers, are competent to bind DNA.

