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Intraperitoneal injection of epidermal growth factor (EGF) into mice resulted in the appearance in liver nuclei of three tyrosine phosphorylated proteins (84, 91, and 92 kilodaltons) within minutes after administration of EGF. Administration of interferon-gamma (IFN-gamma) resulted in the appearance in liver nuclei of two tyrosine phosphorylated proteins (84 and 91 kilodaltons). The 84- and 91-kilodalton proteins detected after either EGF or IFN-gamma administration were identified as the IFN-gamma activation factors (GAF). Furthermore, gel shift analysis revealed that these GAF proteins, detected after either EGF or IFN-gamma administration, specifically bound to the sis-inducible element of the c-fos promoter. Thus, GAF proteins participate in nuclear signaling in both IFN-gamma and EGF pathways.
Ruff-Jamison et al. (Fri,) studied this question.