A small-molecule-based approach to sense codon-templated natural-unnatural hybrid peptides. Selective silencing and reassignment of the sense codon by orthogonal reacylation stalling at the single-codon level.

In the presence of the stable sulfamoyl analogue of phenylalanyl adenylate (Phe-SA), the UUU/UUC sense codon for phenylalanine (Phe) can be silenced and reassigned to a naphthylalanine (Nap) conjugated to tRNAPhe. We have demonstrated the efficiency and selectivity or orthogonality of the Phe-to-Nap reassignment induced by an "orthogonal reacylation stalling" strategy at the single-codon level in the translation of mRNAs of dihydrofolate reductase and a 24-mer oligopeptide. We used a prokaryotic translation system with an essential preincubation, during which the endogenous precharged phenylalanyl-tRNAPhe undergoes deacylation and the reacylation of the resulting tRNAPhe is stalled by the action of Phe-SA to inhibit the phenylalanyl-tRNA synthetase activity. We discuss the significance of the present small-molecule-based approach to sense-codon templated natural-unnatural peptides.