Activation of transcription by IFN-gamma: tyrosine phosphorylation of a 91-kD DNA binding protein.
Interferon-gamma (IFN-gamma) induces the transcription of the gene encoding a guanylate binding protein by activating a latent cytoplasmic factor, GAF (gamma-activated factor). GAF is translocated to the nucleus and binds a DNA element, the gamma-activated site. Through cross-linking and the use of specific antibodies GAF was found to be a 91-kilodalton DNA binding protein that was previously identified as one of four proteins in interferon- stimulated gene factor-3 ( ISGF-3), a transcription complex activated by IFN-alpha. The IFN-gamma-dependent activation of the 91-kilodalton DNA binding protein required cytoplasmic phosphorylation of the protein on tyrosine. The 113-kilodalton ISGF-3 protein that is phosphorylated in response to IFN-alpha was not phosphorylated nor translocated to the nucleus in response to IFN-gamma. Thus the two different ligands result in tyrosine phosphorylation of different combinations of latent cytoplasmic transcription factors that then act at different DNA binding sites.[1]References
- Activation of transcription by IFN-gamma: tyrosine phosphorylation of a 91-kD DNA binding protein. Shuai, K., Schindler, C., Prezioso, V.R., Darnell, J.E. Science (1992) [Pubmed]
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