Effect of spermine on peptide-bond formation, catalyzed by ribosomal peptidyltransferase

The effect of spermine on the binding of AcPhe-tRNA to poly(U)-programmed ribosomes (step 1) and on the puromycin reaction (step 2) has been studied in a cell-free system, derived from E. coli. In the absence of ribosomal wash (FWR fraction) and at suboptimal concentration of Mg++ (6 mM), spermine stimulated the binding of AcPhe-tRNA at least five fold, while at 10 mM Mg++ there was a three fold stimulation. The above stimulatory effect was decreased at 6 mM Mg++, or was abolished at 10 mM Mg++ by the presence of FWR during the binding. Beside the stimulatory effect, spermine enhanced the stability of initiation complex AcPhe-tRNA-poly(U)-ribosome. In step 2, spermine affected the final degree of puromycin reaction and the activity status of peptidyltransferase. Both stimulatory and inhibitory effects have been observed, depending on the experimental conditions followed during the binding of the donor and during the peptide bond formation.