Which types of mutations in the lac operon stop Escherichia coli from utilizing lactose as a carbon source? a) promoter deletion b) lactose-binding site mutation c) repressor DNA-binding site mutation d) operator deletion

D.) repressor DNA-binding site mutation

Explanation:

lacl prevents the repressor polypeptide is a mutant that prevent operon from binding lactose, and thus will bind to the operator and be non-inducible.. This mutant will represses the lac operon whether lactose is present or not and the lac operon will not be expressed. It is also called“super-supperesor".

The lacI locus – One type of mutant allele of lacI (callled I-) prevents the production of a repressor polypeptide or produces a polypeptide that will not allow to bind to the operator sequence.

This is also a constitutive expresser of the lac operon because absence of repressor binding permits transcription.

the correct answer is d