0.53 Bis2a 14.1 bacterial gene regulation  (Page 9/21)

First the Lac promoter would need to be much weaker promoter. Second, the LacI binding site (operator) would most likely need to move to the 5' end of the promoter. Third, when LacI binds to lactose, instead of decreasing the affinity of the protein to the DNA, it would need to increase the binding affinity. Similar to the way CAP-cAMP enhances the binding of CAP. In this hypothetical model, in the presence of lactose, lactose would bind LacI, cause a confirmation change that now stimulates LacI to bind to the promoter region and activate transcription. Hence, the expression pattern would look identical to as it does in the example above, except the mechanism of action by the regulator has changed from negative to positive.