In the tryptophan operon wikipedia page, it says under the Attenuation title:

A similar attenuation mechanism regulates the synthesis of histidine, phenylalanine and threonine.

If my reading is correct, this means that these amino acids also regulate expression of componenets that synthesize them.

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1 Answer 1


The method of inhibition of the operation an anabolic metabolic pathway by the final product synthesized is called:

End-product Inhibition or Feedback Inhibition

Of more biochemical interest is the mechanism, which is:

Allosteric regulation

In general terms, the end product of the pathway is a negative allosteric effector of an early (often the first unique) enzyme of the pathway.

However this is quite distinct from Attenuation. Attenuation regulates the transcription of the trp operon, i.e. the synthesis of the mRNA that encodes the enzymes of the pathway. That summarized above relates to catalytic activity of the already-synthesized enzymes. Attenuation is restricted to prokaryotes†, whereas allosteric regulation is a more general phenomenon.

Although semantically the term “end-product inhibition” could also be applied to attenuation or even repression of transcription, in practice it is not. I do not believe that there is a specific term for attenuation of the transcription of a polycistronic mRNA for synthesis of an amino acid by its tRNA.

End-product inhibition is covered in all biochemistry text books. The best web example I can give that covers all the above terms is from Alberts et al., Molecular Biology of the Cell, freely available on NCBI Bookshelf. This example involves the pathway for the synthesis of CTP, rather than that of an amino acid, the enzyme inhibited being aspartate transcarbamoylase. However the principle is the same.

You can pick up a secondhand copy of an old edition of Berg et al. Biochemistry cheaply on eBay, for example. Well worth it to ready an authoritative account of basic topics in biochemistry, such as this one.

† The reason that attenuation is restricted to prokaryotes is that it depends on the coupling of transcription and translation. In eukaryotes, however, transcription occurs in the nucleus whereas translation occurs in the cytoplasm.


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