Dependence on Potassium Concentration of the Inhibition of the Translation of Messenger Ribonucleic Acid by 7-Methylguanosine 5′-Phosphate

The effects of potassium on the inhibition by 7-methylguanosine 5′-phosphate of the translation in the wheat germ cell-free system of globin mRNA and satellite tobacco necrosis virus (STVN) RNA are examined. The concentration of potassium ion and the anion of the potassium salt both influence the effects of 7-methylguanosine 5′-phosphate on the translation of globin mRNA. If potassium concentrations are less than the optimum for protein synthesis, the inhibition of the translation of globin mRNA by 7-methylguanosine 5′-phosphate is greatly diminished. The inhibition increases as the potassium concentration is increased even after the optimal concentration for protein synthesis is exceeded. At equivalent potassium concentrations, the inhibitory effect of 7-methylguanosine 5′-phosphate on translation of globin mRNA is substantially decreased if potassium acetate is substituted for KCl. However, the optimal concentration for protein synthesis is considerably greater for potassium acetate than for KCl and, if examined at the respective optimal concentrations of these salts for protein synthesis, the inhibiting effects of 7-methylguanosine 57-phosphate are equivalent. The relative importance of the 7-methylguanosine cap for translation of globin mRN A is apparently not decreased at low potassium concentrations since the inhibition of translational activity of globin mRNA resulting from chemical removal of the cap is similar at all potassium concentrations. As expected, inhibition by 7-methylguanosine 5′-phosphate of the translation of STNV RNA, which does not contain a 7-methylguanosine cap, is considerably less than that observed with globin mRNA. However, the inhibition that is observed with STNV RNA exhibits qualitatively the same dependence on the concentration of potassium as that observed with globin mRNA and no inhibition by guanosine 5′-monophosphate is observed. These results illustrate the necessity of optimizing reaction conditions for individual mRNAs if the inhibition of translation of the mRNA by 7-methylguanosine 5′-phosphate is used as a criterion for the presence of a 7-methylguanosine cap.