Trp Operon

Trp Operon

Trp operon is an operon - a group of genes that are used, or transcribed, together - that codes for the components for production of tryptophan. The Trp operon is present in many bacteria, but was first characterized in Escherichia coli. It is regulated so that when tryptophan is present in the environment, it is not used. It was an important experimental system for learning about gene regulation, and is commonly used to teach gene regulation.

Discovered in 1953 by Jacques Monod and colleagues, the trp operon in E. coli was the first repressible operon to be discovered. While the lac operon can be activated by a chemical (allolactose), the tryptophan (Trp) operon is inhibited by a chemical (tryptophan). This operon contains five structural genes: trp E, trp D, trp C, trp B, and trp A, which encode tryptophan synthetase. It also contains a promoter where RNA polymerase binds and a repressor gene (trp R) which synthesizes a specific protein. The protein that is synthesized by trp R then binds to the operator which then causes the transcription to be blocked. In the lac operon, allolactose binds to the repressor protein, allowing gene transcription, while in the trp operon, tryptophan binds to the repressor protein effectively blocking gene transcription. In both situations, repression is that of RNA polymerase transcribing the genes in the operon. Also unlike the lac operon, the trp operon contains a leader peptide and an attenuator sequence which allows for graded regulation.

It is an example of negative regulation of gene expression. Within the operon's regulatory sequence, the operator is blocked by the repressor protein in the presence of tryptophan (thereby preventing transcription) and is liberated in tryptophan's absence (thereby allowing transcription). The process of attenuation (explained below) complements this regulatory action.

Read more about Trp Operon:  Repression, Attenuation, See Also, External Links

Other articles related to "trp operon, trp, operon":

Trp Operon - External Links
... Animation of the Trp operon's regulation. ...
Attenuator (genetics) - The trp Operon
... An example is the trp gene in bacteria ... When the RNA polymerase binds and transcribes the trp gene, the ribosome will start translating ... The attenuator sequence, which is located between the mRNA leader sequence (5' UTR) and trp operon gene sequence, contains four domains, where domain 3 can pair with domain 2 or domain 4 ...
Trp Operon - Attenuation
... Attenuation is a second mechanism of negative feedback in the trp operon ... This allows the process of translation to affect transcription of the operon directly ... At the beginning of the transcribed genes of the trp operon is a sequence of at least 130 nucleotides termed the leader transcript (trpL) ...