sRNA Specificity for Codon Recognition as Studied by the Ribosomal Binding Technique

Fractionation of sRNA from different organisms frequently yields multiple fractions corresponding to one amino acid. It was first shown by Weisblum, Benzer, and Holley (1962) that two different leucine-sRNA fractions are specific for different codons of that amino acid. Thus, in experiments in the cell-free amino acid incorporating system, one fraction transferred leucine into acid-insoluble peptides in the presence of poly UG whereas a second fraction stimulated the incorporation in the presence of poly UC. The specificity of the two leucine-sRNA fractions was further demonstrated in regard to a natural messenger, in that the fractions inserted leucine into different positions in rabbit hemoglobin (Weisblum, Gonano, von Ehren-stein, and Benzer, 1965). Similarly Bennett, Goldstein, and Lipmann (1965) showed differences in the specificity of two serine-sRNA fractions in incorporation experiments directed by poly UC with varying U:C ratios. A similar study was reported by Thiebe and Zachau (1965) with two phenylalanine-sRNA fractions.