A protein synthesizing system from interferon-treated cells that discriminates between cellular and viral messenger RNAs

Abstract

The effect of treating Krebs II ascites tumor cells with interferon on the ability of extracts prepared from them to catalyze the translation of a variety of messenger RNAs was investigated. The following results were obtained: (1) Extracts of untreated cells translated endogenous mRNA, as well as exogenously added synthetic mRNA [poly(U)], cellular mRNA (Krebs cell and L cell), and viral mRNA (reovirus and vaccinia virus). By contrast, extracts of Krebs cells treated in the ascitic form with interferon translated endogenous mRNA, exogenously added cellular mRNA and poly(U) as efficiently as extracts of untreated cells, but they translated viral mRNAs very poorly (less than 10% as efficiently as extracts of untreated cells). Thus, the ability to discriminate between cellular and viral mRNAs that is characteristic of whole cells was also exhibited by these cell-free extracts. (2) Virus infection was not required for the development of the interferon-induced inhibition of viral mRNA translation. (3) Mixing experiments indicated that the inability of extracts of interferon-treated cells to catalyze the translation of viral mRNAs was due to the presence of an inhibitory factor (s) rather than to the absence of a required factor (s). (4) The inhibitory factor (s) was associated with ribosomes, and could be dissociated from them by washing with KC1. (5) Polyacrylamide gel electrophoresis revealed the presence of a 48,000 dalton polypeptide in the 0.3–0.6 M KC1 wash fraction of ribosomes prepared from interferon-treated cells that was not detectable in the corresponding wash of ribosomes prepared from untreated cells. This fraction inhibited the translation of viral mRNAs in cell-free extracts of untreated cells more than any other salt wash fraction. These results suggest that the antiviral activity of interferon is mediated, at least in part, by a ribosome-associated polypeptide that permits discrimination between cellular and viral mRNAs.