The uninducible murine interferon alpha 11 gene (Mu IFN-alpha 11) shows strong homology with the highly inducible Mu IFN-alpha 4 gene in the promoter region. Negative regulatory sequences located between positions -470 and -145 were characterized in the Mu IFN-alpha 11 promoter. The removal of these sequences leads to virus-inducibility of Mu IFN-alpha 11 while their insertion in Mu IFN-alpha 4 corresponding region significantly reduced the inducibility of Mu IFN-alpha 4 promoter. On the other hand, the virus-responsive element (VRE) of the Mu IFN-alpha 11 differs by a single nucleotide substitution at position -78 from the VRE alpha 4. Constructions carrying either VRE alpha 11 or VRE alpha 4 upstream a heterologous promoter displayed different virus inducibilities. The -78 A/G substitution affects the inducibility by decreasing the affinity of VRE-binding trans-regulators. Our results suggest that the combined effect of the negative regulatory sequences and of the mutation in the VRE alpha 11, completely silences the Mu IFN-alpha 11 gene.
The murine interferon-A11 (Mu IFN-A11) gene is a member of the IFN-A multigenic family. In mouse L929 cells, the weak response of the gene's promoter to viral induction is due to a combination of both a point mutation in the virus responsive element (VRE) and the presence of negatively regulating sequences surrounding the VRE. In the distal part of the promoter, the negatively acting E1E2 sequence was delimited. This sequence displays an inhibitory effect in either orientation or position on the inducibility of a virus-responsive heterologous promoter. It selectively represses VRE-dependent transcription but is not able to reduce the transcriptional activity of a VRE-lacking promoter. In a transient transfection assay, an E1E2-containing DNA competitor was able to derepress the native Mu IFN-A11 promoter. Specific nuclear factors bind to this sequence; thus the binding of trans-regulators participates in the repression of the Mu IFN-A11 gene. The E1E2 sequence contains an IFN regulatory factor (IRF)-binding site. Recombinant IRF2 binds this sequence and anti-IRF2 antibodies supershift a major complex formed with nuclear extracts. The protein composing the complex is 50 kDa in size, indicating the presence of IRF2 or antigenically related proteins in the complex. The Mu IFN-A11 gene is the first example within the murine IFN-A family, in which a distal promoter element has been identified that can negatively modulate the transcriptional response to viral induction.
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