Molecular basis of the action of interferon

The interaction of labeled Mengo virus particles with mouse L cells has been studied at very early times after infection. At 30 minutes after infection, a 50 s particle bearing intact viral RNA has been isolated from the cytoplasm of the normally infected cell. This 50 s particle is possibly a complex of viral RNA with the 40 s ribosomal subunit. By study at different intervals after infection, its formation can be related to the assembly of a functional polysome which sediments at 240 s. Viral proteins, including the viral RNA polymerase, are detectable on this complex, although it is not certain that they are synthesized there. Newly formed viral RNA molecules are also processed through the 50 s particle into a similar 240 s polysome.In cells exposed to interferon before infection, the 50 s particle bearing viral RNA is not detected, although a 240 s complex is assembled late in infection. However, this complex does not translate the viral genome to a significant extent, as reflected in a greater than 90% reduction in the synthesis of the viral RNA polymerase and progeny RNA molecules. Although other possibilities are not excluded, the interaction of viral RNA with the smaller ribosomal subunit may be a necessary step in the formation of a functional polysome. The prevention of this interaction may explain the antiviral action of interferon.