A study of the mechanism of ambiguous amino acid coding by poly U: the nature of the products

Abstract

Partial acid hydrolyaates of polypeptides synthesized in vitro under the direction of poly U have been examined by column chromatography. Under conditions where little ambiguity occurs, phenylalanine is incorporated into polypeptide linkage and the only dipeptide observed in partial acid hydrolysates of the polypeptide product is Phe-Phe. High magnesium ion concentrations or the addition of ethanol or streptomycin causes ambiguous coding with poly U, resulting in the incorporation of leucine and/or isoleucine, as well as phenylalanine, into polypeptide. When only leucine and phenylalanine were incorporated (in the presence of the appropriate concentrations of ethanol or magnesium ion), the following dipep-tides were identified in partial acid hydrolysates of thepolypeptideproducts: Phe-Phe, Phe-Leu, Leu-Phe, Leu-Leu. Within the limits of resolution of the method, all of the possible dipeptides of the three amino acids were observed in the degradation products of the polypeptides produced in the presence of streptomycin.