Question

The “Skinny Bacteria” research company has generated a synthetic chemical called "WPT" that binds to LacR and causes a shift in its structure.

Provide a written description for what you think will happen to cellular levels of LacZ if WPT is added to the bacterial growth environment.

Answer 1

• LAC operon of E. coli is an example of inducible gene expression system.

Lac operon includes:

1. Controlling genes:

Promoter- Region for binding of RNA polymerase to initiate transcription of the structural genes present down-stream of the promoter.

Operator- Region where the repressor binds

2. Structural genes- Lac Z- encodes Beta galactosidase. Lac Y- encodes permease, Lac A- encodes transacetylase.

• Lac i represents the repressor and is under a separate promoter and not under lac promoter control.

Lac repressor can recognize three regions of operator.

1. O1 is present within the promoter.
2. O2 is present within lacZ gene 401 bp downstream of O1.
3. O3 in present in lac I gene, which is 93 bp upstream of O1.

• Lac repressor is a tetrameric structure.
• With two of its subunits it binds to O1 and the other two forms loop with O2 or O3.
• In absence of inducer, lac repressor remains bound to the operators. This prevents the RNA polymerase to transcribe the structural genes.
• Lactose (Allolactose) acts as natural inducer.
• Lac repressor has binding site for the inducer.
• Thus, in presence of the inducer, Lac repressor binds with the inducer. This results in a conformational change in the repressor and the repressor does not bind to the operators.
• Thus, the transcription of the structural genes occurs.

• The chemical WPT alters the conformation of the lac repressor.
• Thus, the repressor cannot bind to the operators.
• This will result in continuous transcription of the structural genes.
• As a result there will be a continuous production of Beta galactose from lac Z.