Increase of Fidelity of Polypeptide Synthesis by Spermidine in Eukaryotic Cell‐Free Systems

The mechanism of spermidine‐induced increase of fidelity of polypeptide synthesis in a wheat germ cell‐free system has been studied. It was found that the increase of fidelity in the presence of spermidine occurred mainly at the level of binding of aminoacyl‐tRNA to ribosomes, that reduction of misreading was more marked at the 5′‐base than at the 3′‐base of the codon and that misreading caused by paromomycin and kanamycin C was not significantly decreased by spermidine. It was deduced from these results that spermidine inhibited low‐frequency misreading more strongly than high‐frequency misreading. In addition, spermidine was found to stimulate the rejection of non‐cognate aminoacyl‐tRNA mainly at an initial discrimination step during the binding of aminoacyl‐tRNA to ribosomes, and slightly at a subsequent GTP‐dependent discrimination step, the so‐called proofreading step. In yeast, rabbit reticulocyte, and Artemia salina cell‐free systems, spermidine was found to increase the fidelity of protein synthesis.