Question

The His operon though having a different sequence, utilizes a similar mechanism for regulation. Its leader peptide has the sequence Met-His-Ala-Ile-Phe-His-Ile-His-Gly-Trp-Trp-His-Ser-Thr-Stop. In an experiment you substitute the His leader sequence for the Trp leader peptide (purple region) in the Trp operon. What effect do you think this will have on amino acid attenuation, if any? Provide your rationale.

Answer 1

Yes, there is found attenuation. But in this case, the his codons are found in place of trp codons. That's why attenuation is done with respect to the presence if histidine amino acid. If there is found high concentration of histidine, then there is found inhibition of transcription of structural genes.

But if there is found less concentration of histidine, then there is found cotinuous transcription of structural genes and there is found expression of trp encoding genes. Now, the trp operon's attenuation is dependent on the histidine amino acid. It is not found due to tryptophan amino acid.