Ribosome-catalyzed formation of an abnormal peptide analogue.

The peptidyl-tRNA analogue N-(chloroacetyl)phenylalanyl-tRNAPhe was prepared by chemical aminoacylation and prebound to the P site of Escherichia coli ribosomes in response to poly(uridylic acid). Admixture of phenylalanyl-tRNAPhe to the A site resulted in the formation of two "dipeptides", one of which was formed by displacement of chloride ion from the peptidyl-tRNA. This constitutes the first example of ribosome-mediated formation of a peptide of altered connectivity and suggests a need for revision of the current model of peptide bond formation. Also suggested by the present finding is the feasibility of utilizing tRNAs to prepare polypeptides of altered connectivity in an in vitro protein biosynthesizing system.