Cloning and Promoter Analysis of the Chicken Interferon Regulatory Factor-3 Gene

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Abstract
Interferon regulatory factors (IRFs) are a family of DNA-binding proteins involved in mediating the cellular response to interferons (IFNs) and viral infection. Although extensively studied in mammals, IRFs of other vertebrates have been less well characterized. Previously, we cloned chicken interferon regulatory factor-3 (chIRF-3) mRNA, which is rapidly and transiently induced by double-stranded (ds)RNA. The chIRF-3 mRNA encodes a protein distinct from any known mammalian IRF. Here, we show that chIRF-3 is activated additively by type I and type II IFNs. To delineate the sequence elements required to regulate chIRF-3 expression, we cloned chIRF-3 and 0.48 kb of 5′ flanking sequence. Computer analysis of the proximal promoter revealed three putative binding sites for nuclear factor (NF)-κB, two overlapping interferon-stimulated response elements (ISREs), and an interferon gamma activating sequence (GAS). The presence of both GAS and ISRE consensus sequences in the chIRF-3 promoter is unique among IRF family members. Both type I and II IFNs, as well as dsRNA and IRF-1, trans-activate the promoter in short-term transfection experiments. Mutational analysis of the promoter demonstrated that the putative NF-κB binding sites are needed for stimulation by dsRNA but not by either type I or type II IFN and that both the overlapping ISREs and GAS are required for full induction by type I or type II IFN.

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