The GAS reporter (Luc)-HeLa cell line is designed to monitor the activity of IFN gamma-induced signal transduction pathways in cultured cells by measuring activated STAT1 homodimers. It contains a firefly luciferase gene driven by three copies of the IFN gamma-activated sites (GAS) located upstream of the minimal TATA promoter. IFNγ first binds to a heterodimeric receptor consisting of two chains, IFNGR1 and IFNGR2, causing its dimerization and the activation of specific Janus family kinases (JAK1 and JAK2). Two STAT1 molecules associate with this ligand-activated receptor complex and are activated by phosphorylation to form active homodimer. The active STAT1 homodimers translocate to the nucleus where they bind IFN gamma-activated sites (GAS) in the promoter of IFNγ inducible genes, including luciferase reporter gene.

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