Abstract
The binding of phenylalanyl‐tRNA to purified yeast ribosomes at low magnesium concentrations is dependent upon one of the yeast supernatant transfer factors (factor A). This reaction requires GTP. The GTP analogue guanylyl methylene diphosphonate cannot be substituted for GTP but it acts as a good inhibitor. After incubation of the ribosomes with phenylalanyl‐tRNA, factor A and GTP practically no compound other than phenylalanyl‐tRNA itself is found linked to the ribosomes.In addition to this enzymic type of binding, phenylalanyl‐tRNA is also bound to yeast ribosomes in the absence of factor A and GTP provided that the magnesium concentration is increased to about 20 mM. This non‐enzymic binding is effectively inhibited by deacylated tRNA and this inhibition is prevented if factor A and GTP are included in the incubation mixtures.The binding of N‐acetylphenylalanyl‐tRNA to yeast ribosomes also requires GTP, and is dependent upon factor(s) other than the amino acid transfer factors, which are bound to the ribosomes.

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