STAT1 is a latent transcription factor that functions both as a signal transducer in the cytoplasm and an activator of transcription in the nucleus. It exists as a pair of isoforms, Stat1α (91 kDa) and the splice variant Stat1β (84 kDa). STAT1 is one of seven members of the Signal transducer and activators of transcription (Stats) family. In most cells, both isoforms are activated by IFN-α, but only STAT1α is activated by IFN-γ. The inappropriate activation of STAT1 occurs in many tumors. Serine phosphorylation may be required for the maximal induction of Stat1-mediated gene activation.
