| Abstract: | Spermine and spermidine added to a Saccharomyces cerevisiae cell-free protein synthesizing system increased phenylalanine polymerization reaction several-fold at suboptimal concentration of Mg2+ and approximately two-fold at optimal amounts of Mg2+. The addition of polyamines greatly stimulated the enzymatic and nonenzymatic binding of phenylalanyl-tRNA and N-acetylphenylalanyl-tRNA to ribosomes. The binding of the acetylated derivative was higher than phenylalanyl-tRNA, however, as it was shown the former was bound exclusively to the A site of the ribosome. Contrary to the binding process, the puromycin reaction was not stimulated by spermine added at a concentration which enhanced the polyphenylalanine synthesis. These results indicate that polyamines have not only a sparing effect on the Mg2+ requirement for yeast protein synthesis in vitro and suggest that one of the possible sites of polyamines action might be the binding of aminoacyl-tRNA to ribosomes. |
