Tryptophanase operon leader peptide

UniProtKB accession:  P0AD89

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UniProtKB description:  Required for tryptophan-regulated expression of the tna operon. In the presence of high levels of L-Trp release of this nascent peptide by release factor 2 (RF2, prfB) is inhibited. The ribosome stalls with Pro-24 in the P site and a UGA stop codon in the A site. This prevents transcription termination factor Rho binding, and thus allows transcription and translation of downstream TnaA and TnaB (PubMed:12228716, PubMed:34504068). The presence of TnaC and L-Trp prevents the catalytic GGQ motif of RF2 from engaging with the peptidyl-transferase center (PTC); nucleotides of the PTC are perturbed while Arg-23 probably clashes with 'N5-methyl-Gln-252' of RF2, preventing RF2 from reaching the PTC, and from releasing the translated TnaC peptide (PubMed:34504068, PubMed:34403461). Translation of this peptide turns the ribosome into a small-molecule sensor specifically recognizing L-Trp (PubMed:34504068, PubMed:34403461).