You isolate 20 different O C mutants that are wild type for all other Lac operon

Question

You isolate 20 different OC mutants that are wild type for all other Lac operon genes/regions. You measure relative B-gal production by cells growing under non-induced conditions (glucose) and under induced conditions (lactose). You observe that all of the mutants exhibit a relative B-gal concentration of 100 when grown under induced conditions, but that under non-induced conditions the different mutants exhibit different relative B-gal concentrations ranging from 20 to 100. Give a possible explanation for these observations.

Explanation / Answer

LAC operon is referred toas negative regulation . Lactose is inducer and glucose is non inducer.

Mutants are exhibiting high Bgal con. under induced conditions as the mutation is nonsense .

Under non induced conditions the different mutants are switching over to positive regulation. It is because of catabolite activator protein(CAP). CAP binding site is positive regulatory site. When CAP is bound at this siye it promotes transcription. CAP acts as glucose sensor indirectly through hunger signal molecule cAMP.

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