Interaction of 68-kDa TAR RNA-binding protein and other cellular proteins with prion protein-RNA stem-loop.

The RNA stem-loop structure of the trans-activating region TAR sequence of human immunodeficiency virus-1 mRNA is the binding site for a number of host cell proteins. A virtually identical set of proteins from HeLa nuclear extracts was found to bind to the predicted RNA hairpin element of prion protein (PrP) mRNA, as demonstrated in UV cross-linking/RNase protection and Northwestern assays. We show that the cellular TAR loop-binding protein, p68, is among those proteins which associate with PrP RNA. Competition experiments with various TAR RNA mutants revealed that binding of partially purified p68 to PrP RNA stem-loop occurs sequence-specifically. The 100-kDa 2-5A synthetase which is involved in the cellular antiviral defense was able to bind to PrP mRNA stem-loop in Northwestern blots with cytosolic proteins from HeLa cells treated with interferon. However, the PrP RNA failed to activate this enzyme in vitro, in contrast to TAR RNA.