On the Mechanism of Coded Binding of Aminoacyl-tRNA to Ribosomes: Number and Properties of Sites

Saturation curves for coded binding of amino-acyl transfer RNA (AA-tRNA) to ribosomes ug-gested to us three ribosomal decoding sites in addition to the donor site (Matthaei and Milberg 1967; Matthaei et al., 1968a). Using messenger RNA (mRNA) from the RNA phage fr in a purified initiation system (Matthaei and Swan, unpubl.; Matthaei 1969; Swan and Matthaei 1969a) and thereby supplying each site with a codon for a different amino acid, we have proven the existence of three decoding sites on the same ribosome, in addition to the donor site. The simpler ribosome model generally assumed (Watson 1963), which has only two sites for the binding of tRNA, thus needs to be extended. The originally postulated tw