Respuesta :
A "down" mutation would prevent expression even in the de-repressed state (in the presence of the inducer), resulting in a phenotype that is not inducible.
What would be the effect on transcription of the lac operon?
A lactose sensor is the lac repressor. When lactose is present, it ceases to function as a repressor, blocking transcription of the operon in its usual state. Through its isomer allolactose, the lac repressor indirectly detects lactose. The protein catabolite activator (CAP) serves as a glucose sensor.
If we mutated the laci gene resulting in a mutant lac repressor protein that could bind to the lac operator but not to allolactose, the consequence for transcription of the lac operon would be that an "up" mutation would render the lac operon independent of the cAMP-CAP complex's positive control (when the operon is induced).
Thus from above conclusion we can say that If we mutated the laci gene resulting in a mutant lac repressor protein that could bind to the lac operator but not to allolactose, the consequence for transcription of the lac operon would be that an "up" mutation would render the lac operon independent of the cAMP-CAP complex's positive control (when the operon is induced). A "down" mutation would prevent expression even in the de-repressed state (in the presence of the inducer), resulting in a phenotype that is not inducible.
Learn more about the transcription here:
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