Formation of Peptide Bonds--II: Coding Properties of Leucyl-S-RNAs

Observations on species specificity at the stage of attachment of amino acid to S-RNA have been made by a number of investigators. For example, Benzer and Weisblum (1961) showed that the attachment of amino acid to E. coli S-RNA by enzymes from yeast and rat liver varied, and depended not only on the organism in question but also on the amino acid studied. Apgar and Holley (1962) found that rat liver S-RNA was completely labeled with threonine by rat liver enzyme under conditions that gave no labeling of yeast S-RNA; larger amounts of rat liver enzyme, however, labeled yeast S-RNA with threonine. Berg et al. (1961) demonstrated that yeast enzyme could attach methionine to approximately 40% of the total acceptor sites for methionine in E. coli S-RNA. This was interpreted as evidence for two separate methionine S-RNAs.