Inhibition of Protein Synthesis in Cell-Free Systems from Interferon-Treated, Infected Cells: Further Characterization and Effect of Formylmethionyl-tRNA(F).

The translation of encephalomyocarditis virus (EMC) RNA is markedly inhibited in cell-free systems from interferon-treated, vaccinia virus-infected L-cells (10, 11). The polypeptide products synthesized in response to EMC RNA in cell-free systems from these and untreated infected cells have been analyzed by electrophoresis on polyacrylamide gels. Qualitatively, the same EMC-specific polypeptides were synthesized throughout. In experiments using preincubated microsomes from normal Krebs cells to assay cell sap from L-cells which had been exposed to interferon prior to infection, only the amount of the EMC-specific polypeptide products was reduced. This result suggests that there is an inhibition very early in translation in interferon-treated, infected cells. Initiation seems a priori the more attractive site for this inhibition, but an effect shortly after initiation cannot be excluded. With unfractionated cell-free systems from interferon-treated infected L-cells, however, there appeared to be an additional minor inhibitory effect on polypeptide chain elongation, in that the EMC-specific polypeptides synthesized showed not only a reduction in amount but also a bias towards lower molecular weight. The formylated methionyl initiator tRNA (Fmet-tRNA(F)) was used as a further probe into the apparent effect on intiation. With this reagent we have confirmed that there is one major initiation site for the translation of EMC RNA in these cell-free systems. In addition, the results have shown that EMC-specific polypeptide chains initiated with Fmet escape the major interferon-mediated inhibition at or shortly after initiation.