Association of STATs with relatives and friends

Members of the STAT family of transcription factors are present in species as diverse as mammals, insects and slime molds. Discovered as mediators of interferon-induced signals, the STATs were later shown to drive many differ ent ligand-induced responses through receptor-induced tyrosine phosphorylat ion and dimerization. STAT1 also functions as a transcription factor, essen tial for the efficient constitutive expression of certain genes, without ne eding tyrosine phosphorylation, and phosphorylated STAT1 dimers mediate sup pression - rather than activation - of some genes. STATs are present in the cytoplasm of untreated cells in multiprotein complexes, which might aid in their nuclear translocation and differential binding to DNA, thus contribu ting to the specificity of STAT action.