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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 regulator gene called trpR. When tryptophan is present, the trpR protein binds to the operator, blocking transcription of the trp operon by RNA polymerase.
The trp operon consists of a regulatory gene, a promoter, an operator, and a terminator. The trp operon is active only when cellular tryptophan is scarce. If there isn't enough tryptophan, the repressor protein breaks off from the operator (where the repressor is normally bound) and RNA polymerase can complete its reading of the strand of DNA ...
The formation of the terminator requires the trp RNA-binding attenuation protein (TRAP protein) in species of Bacillus and related bacteria. This protein is encoded by the MtrB gene. [2] TRAP protein forms an oligomer of 11 subunits, in the presence of tryptophan this binds to section of RNA containing 11 (G/U)AG repeats.
A high level of tryptophan will permit ribosomes to translate the attenuator sequence domains 1 and 2, allowing domains 3 and 4 to form a hairpin structure, which results in termination of transcription of the trp operon. Since the protein coding genes are not transcribed due to rho independent termination, no tryptophan is synthesised.
Tryptophan (symbol Trp or W) [3] is an α-amino acid that is used in the biosynthesis of proteins. Tryptophan contains an α -amino group, an α- carboxylic acid group, and a side chain indole , making it a polar molecule with a non-polar aromatic beta carbon substituent.
This operon contains five structural genes: trp E, trp D, trp C, trp B, and trp A, which encodes tryptophan synthetase. It also contains a promoter which binds to RNA polymerase and an operator which blocks transcription when bound to the protein synthesized by the repressor gene (trp R) that binds to the operator.
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One copy entered the trp operon as trpB2i allowing for its expression with trpA. TrpB2i formed transient complexes with TrpA and in the process activated TrpA unidirectionally. The other copy remained outside as trpB2o, and fulfilled an existing role or played a new one such as acting as a salvage protein for indole.