Proteins of transcription factor ISGF-3: one gene encodes the 91-and 84-kDa ISGF-3 proteins that are activated by interferon alpha.

ISGF-3 is an interferon-dependent positive-acting transcription factor that is cytoplasmically activated, possibly through direct interaction with the interferon receptor. The factor has been purified, its component proteins have been separated, and its peptide sequences have been obtained. From the sequences, degenerate oligonucleotide probes were constructed to screen for cDNA clones. Sequencing of the selected clones shows that the 91- and 84-kDa components represent two forms of a previously unknown (to our knowledge) protein. Several antibodies raised against these proteins prove that they indeed do encode protein components of ISGF-3. This work provides reagents to explore the modification of this cytoplasmically activated transcription factor.