A gamma-interferon-induced factor that binds the interferon response sequence of the MHC class I gene, H-2Kb.

Transcription of class I genes of the major histocompatibility complex (MHC) can be induced by interferons. Treatment of HeLa cells with interferon-gamma induces a DNA-binding factor, IBP-1, specific for a site within the interferon response sequence (IRS) of the H-2Kb promoter. The mol. wt of IBP-1, as estimated by photoactivated protein-DNA crosslinking analysis, is approximately 59 kd. Point-mutation of this binding site abolishes IBP-1 interaction and the ability of the MHC promoter to respond to interferon. Induction of this binding activity is rapid and closely parallels the previously reported time course of transcriptional activation of endogenous MHC class I genes. Treatment of cells with cycloheximide, a protein synthesis inhibitor, blocked the induction of the DNA-binding activity. An oligonucleotide derived from the virus- and double-stranded RNA-inducible promoter of the interferon-beta 1 gene is able to bind IBP-1. Sequences similar to the IBP-1 binding site are found upstream of many interferon-responsive genes.