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#leader peptide

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Gene regulation in Prokaryotes

Length of leader peptide in trp operon is about

Leader peptide consists of only fourteen amino acids encoded within first fifty codons of 162-nucleotide leader transcript located upstream of attenuator hairpins and structural genes. Short length ensures translating ribosome remains physically close to transcribing RNA polymerase, maintaining one-to-one coupling necessary for attenuation mechanism to function responsively. Despite brevity, sequence includes Trp-rich sensing codons plus translation termination signal for controlled ribosome release. Approximate length of fourteen residues balances minimal translational cost and rapid synthesis with sufficient coding capacity to embed critical regulatory tryptophan codons and still allow formation of four complementary RNA regions controlling termination versus readthrough choice.

Ref: Berg Biochemistry 8e Ch 31 – leader peptide is 14 amino acids with two Trp residues regulating attenuation.

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Gene regulation in Prokaryotes

Leader peptide of trp operon contains

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.

Ref: Berg Biochemistry Ch31; Hartwell Genetics Ch11: trp leader 14 aa includes two adjacent Trp codons for attenuation sensing.

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