Poliovirus Mutant That Does Not Selectively Inhibit Host Cell Protein Synthesis

Abstract

A poliovirus type I (Mahoney strain) mutant was obtained by inserting three base pairs into an infectious cDNA clone. The extra amino acid encoded by the insertion was in the amino-terminal (protein 8) portion of the P2 segment of the polyprotein. The mutant virus makes small plaques on HeLa and monkey kidney (CV-1) cells at all temperatures. It lost the ability to mediate the selective inhibition of host cell translation which ordinarily occurs in the first few hours after infection. As an apparent consequence, the mutant synthesizes far less protein than does wild-type virus. In mutant-infected CV-1 cells enough protein was produced to permit a normal course of RNA replication, but the yield of progeny virus was very low. In mutant-infected HeLa cells there was a premature cessation of both cellular and viral protein synthesis followed by a premature halt of viral RNA synthesis. This nonspecific translational inhibition was distinguishable from wild-type-mediated inhibition and did not appear to be part of an interferon or heat shock response. Because the mutant is recessive, our results imply that (at least in HeLa cells) wild-type poliovirus not only actively inhibits translation of cellular mRNAs, but also avoids early inhibition of its own protein synthesis. Cleavage of the cap-binding complex protein P220, which has been associated with the selective inhibition of capped mRNA translation, did not occur in mutant-infected cells. This result supports the hypothesis that cleavage of P220 plays an important role in normal poliovirus-mediated translational inhibition.

TIF4631 and TIF4632: Two Yeast Genes Encoding the High-Molecular-Weight Subunits of the Cap-Binding Protein Complex (eukaryotic initiation factor 4F) Contain an RNA Recognition Motif-Like Sequence and Carry out an Essential Function

“…The available data derived from translational studies with poliovirus-infected cells indicate that p220 is important for cap-dependent translation. Shutoff of host protein synthesis in poliovirus-infected cells has been linked to virus-induced cleavage of p220 (9,81). Consistent with this, addition of intact eIF-4F to cell extracts prepared from poliovirusinfected cells rescues cap-dependent translation (21,84).…”

Evidence that the SKI Antiviral System of Saccharomyces cerevisiae Acts by Blocking Expression of Viral mRNA

“…Poliovirus mRNA (free [plus] strand) is uncapped (2), and the poliovirus 2A protease leads to cleavage of one component (p220) of the cap-binding protein complex, thereby specifically turning off host translation (5,42). Our hypothesis for the mechanism of action of the SKI products is the converse of this: the host defends itself from viruses by recognizing their transcripts as viral or nonself by the absence of the 5' cap or 3' poly(A) structure and limiting their translation.…”