- The trp promoter is a naturally occurring promoter derived from the tryptophan (trp) operon of Escherichia coli, which controls genes involved in tryptophan biosynthesis.
- It is regulated by the TrpR repressor, a protein that binds to the operator region of the promoter in the presence of L-tryptophan.
- When tryptophan levels are high, TrpR forms a repressor-tryptophan complex that inhibits transcription by blocking RNA polymerase binding. Conversely, in the absence of tryptophan, TrpR does not bind to the operator, allowing transcription to proceed. This system provides feedback repression that is sensitive to tryptophan levels in the cell.
- In recombinant expression systems, the trp promoter has been used for moderately strong and tightly regulated gene expression. Its activity can be induced simply by growing cells in tryptophan-depleted medium, making it useful in certain biotechnological or metabolic engineering applications.
- However, the trp promoter is less commonly used than more modern systems like T7 or Ptac, as it requires careful manipulation of medium composition and can be affected by endogenous metabolic regulation.
- Nevertheless, it forms the basis of synthetic hybrid promoters such as Ptac, where its strong transcription initiation sequence is combined with more easily inducible regulatory elements.
- The native trp promoter remains of historical and functional interest in understanding bacterial gene regulation and for use in applications where nutrient-responsive control is desired.
