Polypeptide chain initiation and the characterization of ribosomal binding sites in E. coli.

Abstract

The two reacting intermediates which are involved in the addition of an amino acid residue to a growing polypeptide are the aminoacyl-sRNA and the polypeptidyl-sRNA (Hoagland et al., 1958; Hecht et al., 1959; Berg and Ofengand, 1958; Gilbert, 1963; Bretscher, 1963, 1965). This extension process occurs on ribosomes (Littlefield et al., 1955) and requires a messenger RNA (Brenner et al., 1961; Gros et al., 1961), at least two enzymes (Nathans and Lipmann, 1961), GTP (Keller and Zamecnik, 1956) and a suitable inorganic environment. Both sRNA molecules, bearing either the peptidyl or aminoacyl groups, must be bound to the ribosome as peptide bond formation takes place. This model requires that there are at least two sites on a ribosome capable of binding an sRNA molecule—one for the peptidyl-sRNA (in the “peptide site”) and one for the aminoacyl-sRNA (in the “amino acid site”). This is shown schematically in Fig. 1.