Reversal of the inhibitory effects of the pokeweed antiviral protein upon protein synthesis.

Protein synthesis directed by natural mRNA is more sensitive to the inhibitory action of the pokeweed antiviral protein than synthesis directed by poly-(uridylic acid). Investigations into the nature of this difference revealed that pokeweed antiviral protein does not inhibit the initiation stage of protein synthesis and that the expression of pokeweed antiviral protein inhibition is dependent upon the K+ and Mg2+ concentrations used in the protein synthesis assay. Ribosomes treated with pokeweed antiviral protein function as efficiently as untreated ribosomes if assayed at either high Mg2+ or low K+ concentrations. The influence of ionic conditions upon the individual elongation factor reactions shows that pokeweed antiviral protein inhibition of the elongation factor two translocation reaction is sensitive to ionic conditions but that the inhibition of the elongation factor one-mediated enzymatic binding is not sensitive to changes in these conditions. The results suggest that the unknown enzymatic effect of pokeweed antiviral protein produces a conformational change in ribosome, which is reversed under conditions which favor a more compact ribosomal structure.