VIRUS-MEDIATED INDUCTION OF INTERFERON-A GENE REQUIRES COOPERATION BETWEEN MULTIPLE BINDING-FACTORS IN THE INTERFERON-ALPHA PROMOTER REGION

Transcriptional activation of interferon A (IFNA) gene in virus-infect ed cells is controlled by a 35-nucleotide inducible element that is ce ll type specific. Within this region, two elements, alphaF1 and IRF-1 binding sites, were shown by mutation analysis to play a crucial role in the expression of inducible element. In this study, we have analyze d the binding of nuclear proteins to the alphaF1 sequence and have sho wn that the induction is associated with the formation of a novel comp lex alphaF1/B, which contains at least two DNA binding proteins of 68 and 96 kDa. In contrast, no binding of the purified interferon regulat ory factor 1 (IRF-1) either to the alphaF1 or IRF-1 binding sites coul d be detected in vitro. However, the oligonucleotides corresponding to alphaF1 or IRF-1 binding sites competed efficiently for the induction of IFNA4 promoter region in a transient transfection assay. We sugges t that the induction of IFNA promoter region requires cooperation betw een alphaF1 binding proteins and IRF-1. Interestingly, our data also s how that the inability of IFNA6 promoter to be expressed in infected L -cells may be a result of a viral-induced repressor, which could act b y binding and inactivating alphaF1 or by competing for the IRF-1 bindi ng site. These results suggest that cell-specific expression of IFNA g enes results from corecruitment of trans-acting factors that bind to a lphaF1 and the IRF-1 binding site with the cell-specific virus-induced activator or repressor.