Gene regulation in prokaryotes/Trp operon

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The Repressible Tryptophan Operon[edit | edit source]

trpR[edit | edit source]

The trp repressor gene, trpR, is not closely linked to the trp operon and trpR protein is always produced. In the presence of tryptophan, trpR repressor protein undergoes a conformational changes and binds to the operator, preventing transcription.

trpL and Attenuation[edit | edit source]

The trpL region lies 5' to the genes that encode tryptophan synthetic enzymes. Attenuation results from premature termination of trp RNA at the attenuator sequence in trpL and requires tryptophan-charged tRNATrp. RNA transcribed from the attenuator sequence forms a hairpin.

The 162 nucleotide trp leader contains four regions that can base pair with itself and for alternative stem-loop structurs.

The leader sequence contains a short open reading frame coding for a 14 amino acid peptide followed by a stop codon. This peptide includes two consecutive trp codons. The production of this peptide is modulated by the availability of charged tRNATrp

Low Tryptophan[edit | edit source]
High Tryptophan[edit | edit source]