In general, the nuclear import and export of proteins and nucleic acids requires transport receptors known collectively as karyopherins. However, nuclear export of most mRNAs is mediated by the non-karyopherin mRNA receptor TAP. Now, on , Jun-Ichi Fujisawa and colleagues report that the nuclear export of interferon-α1 (IFN-α1) mRNA is mediated by CRM1, a karyopherin more often involved in the export of proteins (including the HIV-1 Rev protein), U-rich small nuclear RNAs, and rRNAs. The authors show that the nuclear export of IFN-α1 mRNA is inhibited by overexpression of Rev, provided the protein carries an intact nuclear export signal, and by two inhibitors of CRM1 function. In addition, IFN-α1 mRNA colocalizes with CRM1 but not TAP in the nucleus. Surprisingly, the adenylate/uridylate-rich element (ARE) in the 3′ untranslated region of IFN-α1 mRNA is not required for its nuclear export; in other mRNAs whose export is CRM1 dependent, the RNA adaptor HuR mediates export by binding to the ARE. Thus, a new RNA adaptor may be required for CRM-1-dependent nuclear export of IFN-α1 mRNA.
