65-kDa protein binds to destabilizing sequences in the IFN-beta mRNA coding and 3' UTR.

The transient expression of human interferon (IFN-beta) gene in response to viral induction is regulated both at the transcriptional and posttranscriptional levels. The decrease in levels of IFN-beta mRNA, which requires protein synthesis, is due to transcriptional repression as well as a rapid turnover of beta mRNA. Previous studies have shown the presence of two destabilizing sequences, one in the 3' untranslated region (UTR) and the other in the coding region. We have shown in this study that the coding region destabilizing element resides in the 3' end of the coding region (+538 to +637) and that the degradation does not require the translation of IFN-beta mRNA through its coding region. In addition, we have identified three domains of 19, 20, and 29 nucleotides long that specifically bind a 65-kilodalton (kDa) cytoplasmic protein. One of the binding sites is in the 3' end of the coding region and the other two in the 3' UTR. All these regions are AU-rich and show considerable homology to each other. Interestingly, the levels of the 65-kDa protein was increased after poly rI.rC induction. We suggest that this 65-kDa protein is a component of the IFN-beta mRNA destabilizing complex or plays a role in the degradation of IFN-beta mRNA.