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This term has been used in several different ways.
( - 1- ) gamma-interferon activation factor
GAF is a transcription factor (see: Gene expression ) specifically induced by treatment of cells with IFN-gamma (see also: IFN ).
GAF exists in the cytoplasm in a latent form and is activated by phosphorylation immediately after binding of IFN-gamma to its receptor. Phosphorylation of GAF is mediated by an IFN-regulated tyrosine kinase (see also: PTK ; protein tyrosine kinase ). The phosphorylated GAF protein translocates to the nucleus and specifically recognizes a nucleotide sequence, calledGAS ( gamma-interferon activation site) found in the promoter region of genes the expression of which is induced by IFN-gamma . This site overlaps with the interferon-stimulated response element , ISRE (see: IRS ) which is involved also in transciptional activation of genes induced by interferons .
The DNA-binding moiety of GAF is an IFN-responsive protein of 91 kDa (p91 ) which is also phosphorylated in response to IFN-alpha . It participates in the formation of the IFN-alpha-regulated transcriptional activator ISGF-3 (see also: IRS , interferon response sequence ).
( - 2- ) glia activating factor
see: FGF-9 .
(- 1-) gamma-interferon activation factor
Decker T et al Cytoplasmic activation of GAF, an IFN-gamma-regulated DNA-binding factor EMBO Journal 10: 927-32 (1991); Eilers A et al The response of gamma interferon activation factor is under developmental control in cells of the macrophage lineage. Molecular Cellular Biology 13: 3245-54 (1993); Shuai K et al Interferon gamma triggers transcription through cytoplasmic tyrosine phosphorylation of a 91 kDa DNA-binding protein. Science 258: 1808-12 (1992)