The Lactose Operon—A Case Study in Regulation

Repressor binding to operator prevents transcription of lacZYA 

Repressor inactivated by binding with lactose metabolite 

Active repressor from copy 2 can bind to operators normally Both operons controlled normally 

This model also accounts for the behavior of mutants that cause repressor to fail to bind inducer. If the repressor can t bind inducer, then the lac genes it controls are permanently turned off because repressor will be bound to the operator whether inducer is present or not. In a diploid situation, both sets of genes will be turned off, because the repressor will bind to both operators. 

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