Gene regulation in prokaryotes/Trp operon
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