Mechanism for discrimination between viral and host mRNA in interferon-treated cells.

In extracts of interferon-treated HeLa cells, RNA covalently linked to double-stranded RNA (dsRNA) is preferentially degraded compared with mRNA not linked in dsRNA. This was established by following the degradation of poly(A)-containing mRNA annealed with poly(U), of poly(C)-containing encephalomyocarditis virus RNA annealed with poly(I), and of the replicative intermediate of the virus isolated from infected cells. In extracts of interferon-treated cells, dsRNA promotes the synthesis of a series of oligonucleotides, designated (2'-5')oligo(A), which in turn activate an endonuclease. Several lines of evidence suggest that the (2'-5')oligo(A) polymerase/endonuclease system is involved in the preferential degradation of mRNA linked to dsRNA. Conditions that prevent synthesis of (2'-5')oligo(A) prevent this preferential degradation, whereas addition of (2'-5')oligo(A) or conditions that favor its synthesis result in degradation of mRNA both linked and not linked to dsRNA. These results are best explained by a localized activation of the endonuclease near the dsRNA region of our model substrates. We propose that in infected cells activation of the endonuclease takes place near the replicative intermediates of RNA viruses. The replicative intermediates of encephalomyocarditis virus promote synthesis of (2'-5')-oligo(A) in extracts of interferon-treated cells and are degraded to a 20S "core" resistant to digestion with RNase A. This mechanism may be responsible for discrimination between viral and cellular mRNA in interferon-treated cells.