The Binding of Peptidyl‐tRNA and Acylaminoacyl‐tRNA to E. coli Ribosomes

The non‐enzymatic binding of aminoacyl‐tRNA, N‐blocked aminoacyl‐tRNA, peptidyl‐tRNA and N‐blocked peptidyl‐tRNA to E. coli ribosomes was measured at 0.01 M magnesium ion concentration in the presence of poly U. It was found that the maximal amounts of phenylalanyl‐tRNA and peptidyl‐tRNA, that can be bound to the ribosomes are the same, but the amounts of N‐blocked phenylalanyl‐tRNA and N‐blocked peptidyl‐tRNA, that can maximally be bound to the ribosomes are much less. Phenylalanyl‐tRNA and peptidyl‐tRNA can be bound to ribosomes which are saturated in respect to N‐blocked phenylalanyl‐tRNA or N‐blocked peptidyl‐tRNA; however, the presence of the N‐blocked substrates on the ribosomes partially inhibits the additional binding of phenylalanyl‐tRNA or peptidyl‐tRNA. Aminoacyl‐tRNA added to ribosomes saturated with respect to peptidyl‐tRNA, partially displaces the peptidyl‐tRNA from its ribosomal binding site. Under the same conditions, peptidyl‐tRNA exchanges with prebound aminoacyl‐tRNA considerably less.