Practice question

Leader peptide region trpL encodes specific amino acid sequence Met-Lys-Ala-Ile-Phe-Val-Leu-Lys-Gly-Trp-Trp-Arg-Thr-Ser including tandem UGG UGG tryptophan codons at positions ten and eleven of fourteen. Occurrence of adjacent Trp codons is extremely rare because tryptophan comprises roughly one percent of Escherichia coli proteome and encoded solely by single codon UGG, making double occurrence statistically unusual. Paired motif creates exceptionally sensitive metabolic sensor: low availability of charged tryptophan tRNA causes ribosome stalling at these positions, while sufficient charged species allows rapid readthrough, making dipeptide core central regulator of attenuation decision and downstream structural expression.