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Allolactose acts as a signal molecule that binds to the LacI protein (repressor) and prevents it...

Allolactose acts as a signal molecule that binds to the LacI protein (repressor) and prevents it from binding to the Operator on the lac operon. But if the repressor is on the operator, no B-glactosidase can be made which means no allolactose can be made in the first place. So how is the repressor removed so allolactose can be made to stop the repressor from binding?

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Answer #1

Cells always have a basal level of β-galactosidase.

Upon increase/introduction in lactose levels inside the cells, this basal amount of β-galactosidase converts few molecules of lactose into allolactose which binds to Lac repressor. Binding of allolactose to Lac repressor prevents the repressor from binding to the lac operon operator thereby promoting its expression.

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