A theoretical operon ( amo ) in E. coli contains several structural genes encodi

Question

A theoretical operon (amo) in E. coli contains several structural genes encoding enzymes involved in the biosynthesis of a particular amino acid. Unlike the lac operon, in which the repressor gene is separate from the operon itself, for the amo operon, the repressor gene is found within the operon itself. When the end product amino acid is present, it binds to the repressor, and this complex binds to the operator, repressing the operon. In the absence of the amino acid, the repressor fails to bind to the operator, and transcription proceeds.

Characterize this operon, comparing it to the regulation of the lac and trp operons. Be sure to discuss how regulation is affected by having the repressor gene as part of the operon. Then, consider the following mutations:

a) Mutation in the operator region;

b) Mutation in the promoter region;

c) Mutation in the repressor gene.

In each case, state whether the operon will be transcribed or not, and describe how the mutation affects the regulation of the operon. Compare each response to the equivalent situation in the lac and trp operons.

Explanation / Answer

1) mutation in operator region will cause neither the repressor nor the amino acid coding genes to be transcribed or if the mutation is such that it will alter the site for binding of the repressor it will lead to formation of constitutive operator that will constantly synthesize amino acids. as the situation in lac operator mutation.

2) promoter mutation will cause neither the repressor nor the amino acid coding genes to be transcribed because even the repressor is coded for the operon region itself. as in lac operon

3) if only repressor gene is mutated then there will be constant synthesis of amino acid as there will be no repressor to which the amino acid can bind and repress the synthesis process.

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