Tryptophan Operon of Escherichia coli

The trp operon of E. coli contains five major structural genes encoding all seven protein functional domains necessary for tryptophan biosynthesis from the common aromatic precursor, chorismate. Transcription of the trp operon is highly regulated. Initiation of transcription at the trp promoter is regulated by the tryptophan-activated trp repressor. The repressor can bind at multiple operator sites located in the promoter region. Transcription of the structural genes of the trp operon also is regulated by transcription attenuation, in response to the accumulation of uncharged tRNA Trp . When this uncharged tRNA accumulates, it leads to ribosome stalling during attempted translation of the leader peptide coding region. This leads to the formation of an RNA antiterminator structure that prevents the RNA terminator structure from forming. Absence of the terminator structure allows polymerase to continue transcription into the structural genes of the operon. When there are adequate levels of charged tRNA Trp in the cell, the ribosome translating the leader peptide coding region completes leader peptide synthesis, allowing the RNA terminator structure to form, and terminate transcription.