Tryptophan repressor (or trp repressor) is a transcription factor involved in controlling amino acid metabolism. It has been best studied in Escherichia coli, where it is a dimeric protein that regulates transcription of the 5 genes in the tryptophan operon. When the amino acid tryptophan is plentiful in the cell, it binds to the protein, which causes a conformational change in the protein. The repressor complex then binds to its operator sequence in the genes it regulates, shutting off the genes.
One of the genes regulated by trp repressor, trpR, codes for the tryptophan repressor protein. This is a form of feedback regulation.
The (tryptophan) repressor is a 25 kD protein homodimer which regulates transcription of the tryptophan biosynthetic pathway in bacteria. There are 5 operons which are regulated by trpR: the trpEDCBA, trpR, AroH, AroL, and mtr operons.
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