The Effect of Salt Concentration on the Inhibition of Protein Synthesis by Double‐Stranded RNA

Double‐stranded RNAs (dsRNA) such as poly(I) · poly(C) inhibit protein synthesis in reticulocyte lysate incubated with low concentrations of potassium salts more than in lysate incubated with higher concentration of salt. The inhibition of protein synthesis by dsRNA takes place after an initial lag. In the presence of high salt concentrations the lag period before the inhibition occurs is considerably increased. The maximum inhibitory concentration of poly(I) · poly(C) remains the same at all salt concentrations tested; high concentrations of dsRNA are not inhibitory under different ionic conditions. The inhibition of protein synthesis by dsRNA is due to a loss of the Met‐tRNA f binding activity of native 40 S ribosomal subunits. However, lysates incubated with dsRNA at high salt concentrations retain Met‐tRNA f binding activity. Initiation factors(elF) isolated from ribosomes of lysates incubated under different ionic conditions have been used to determine the activity of the initiation factor, elF‐2, which catalyzes the binding of Met‐tRNA f to 40‐S subunits. The initiation factors from lysates incubated with poly(I) · poly(C) at low salt concentrations are less active in binding Met‐tRNA f and GTP than those from lysates incubated at high salt concentrations. Ribosomes washed with 0.5 M KCl obtained from these lysates are equally active in binding Met‐tRNA f to 40‐S subunits when supplemented with fresh initiation factors, indicating that the loss in Met‐tRNA f binding activity is due to a loss in initiation factor activity and not to a loss of any 40‐S subunit activity. The decreased inhibitory activity of dsRNA at high salt concentrations is due both to a delay in the formation of a dsRNA‐activated inhibitor, and to a reduced effect on protein synthesis of the inhibitor.