trp operon

The trp <a href="/facts/Operon/0m7pJKWn">operon</a> is a group of genes that are transcribed together, encoding the enzymes that produce the amino acid <a href="/facts/Tryptophan/JcUxlxAh">tryptophan</a> in bacteria. The trp operon was first characterized in <a href="/facts/Escherichia_coli/nR4Gvl56">Escherichia coli</a>, and it has since been discovered in many other bacteria. The operon is regulated so that, when tryptophan is present in the environment, the genes for tryptophan synthesis are repressed.
The trp operon contains five structural genes: trpE, trpD, trpC, trpB, and trpA, which encode the enzymes needed to synthesize tryptophan. It also contains a repressive <a href="/facts/Regulator_gene/oH86M9nI">regulator gene</a> called trpR. When tryptophan is present, the trpR protein binds to the <a href="/facts/Operator_(biology)/0m7pJKWn">operator</a>, blocking transcription of the trp operon by RNA polymerase.
This operon is an example of <a href="/facts/Operon/0m7pJKWn">repressible negative regulation</a> of gene expression. The <a href="/facts/Repressor/qGBBQwqS">repressor</a> protein binds to the <a href="/facts/Operator_(biology)/0m7pJKWn">operator</a> in the presence of tryptophan (repressing <a href="/facts/Transcription_(genetics)/bDgp9HDN">transcription</a>) and is released from the operon when tryptophan is absent (allowing transcription to proceed). The trp operon additionally uses <a href="/facts/Attenuation_of_transcription/alCPohLR">attenuation</a> to control expression of the <a href="/facts/Operon/0m7pJKWn">operon</a>, a second <a href="/facts/Negative_feedback/G9byVgpN">negative feedback</a> control mechanism.
The trp operon is well-studied and is commonly used as an example of gene regulation in bacteria alongside the <a href="/facts/Lac_operon/yqfv82qV">lac operon</a>.

trp operon open-in-new

trp operon