Explain the circumstances under which attenuation of operon gene expression is advantageous to a bacterial organism. Would you expect attenuation to be found in a single-celled eukaryote? In a multicelled eukaryote?

Identify similarities and differences between an inducible operon and a repressible operon in terms of

The presence and action of allosteric regulatory molecules.

Identify similarities and differences between an inducible operon and a repressible operon in terms of

The organization of structural genes of the operon.

Is attenuation the product of an allosteric effect? Is attenuation the result of a transcriptional or a translational activity? Explain your answers.

The trpL region contains four repeated DNA sequences that lead to the formation of stem-loop structures in mRNA. What are these stem-loop structures, and how do they affect transcription of the structural genes of the trp operon?

Attenuation of trp operon transcription is controlled by the formation of stem-loop structures in mRNA. The attenuation function can be disrupted by mutations that alter the sequence of repeat DNA regions 1 to 4 and prevent the formation of mRNA stem loops. Describe the likely effects on attenuation of each of the following mutations under the conditions specified.

A repressible operon system, like the trp operon, contains three genes, G, Z, and W. Operon genes are synthesized when the end product of the operon synthesis pathway is absent, but there is no synthesis when the end product is present. One of these genes is an operator, one is a regulatory protein, and the other is a structural enzyme involved in synthesis of the end product. In the table below, '+' indicates that the enzyme is synthesized by the operon and '−' means that no enzyme synthesis occurs. Use this information to determine which gene corresponds to each operon function.