You are investigating a newly discovered operon in bacteria

You are investigating a newly discovered operon in bacteria. This operon has two genes that are regulated together under the control of a single promoter and a single transcription factor. There are five regions: A regulatory gene for the transcription factor protein A promoter for the structural genes in the operon A binding site for the transcription factor A structural gene for an enzyme (Gene 1) A structural gene for a channel protein (Gene 2) Expression of the wild-type operon Is dependent on an external signal, namely the presence or absence of an ammo acid. To determine the function of different regions of this segment of DNA. you make mutations and determine the effect on protein production in the presence and absence of the signal. The results are shown In the table. A plus sign (+) indicates the functional protein Is made; a minus sign (-) indicates that no functional protein is made. What is the identity of region D7 Select all possible options.

Solution

Answer:

Region D:

Mutation in region D induces constitutive expression of gene1 and gene2, that is the the two structural genes gets expressed both in the presence or absence of the signal.

There can be two mutations which can cause such an effect.

1. Mutation in the promoter:

The mutation causes base changes such that the promoter no longer responds to the transcription factor protein and as such functions constitutively.

2. Mutation in the regulatory gene for the transcription factor protein:

Mutation in the regulatory gene encoding the transcription factor is such that it is no longer functional. So, it does not bind to the operator (binding site of transcription factor) thus leading to constitutive expression.

3. Mutation in the Operator (Binding site of transcription factor):

Mutation in the operator can prevent the binding of the transcription factor, resulting in constitutive expression.

So, region D can be options A, B and C.