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 amino 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 that a functional protein is made; a minus sign (-) indicates that no functional protein is made. Based on the effect of mutating the transcription factor gene and the binding site for the transcription factor, what do you now know about how this operon is regulated?Select all that apply. A. The transcription factor is a repressor. B. The transcription factor is an activator. C. The operon is under negative inducible regulation. D. The operon is under negative repressive regulation. E. The operon is under positive inducible regulation. F. The operon is under positive repressible regulation.

Solution

According to the results shown in the table above:

The transcription factor is a repressor and the operon is under negative inducible regulation.

{From the table:

1. Region A i.e. A regulatory gene for transcription factors protein indicates a negative sign which means no functional protein is made hence, the transcription factor is a repressor.

2. Region B, i.e. a promoter for the structural genes in the operon also shows a negative sign indicating an inducible operon under negative control ( the operon is normally \"off\" and it gets turned on by the repressor releasing the DNA at the downstream operator site.}

Points to remember