Which types of mutations in the lac operon stop Escherichia coli from utilizing

Question

Which types of mutations in the lac operon stop Escherichia coli from utilizing lactose as a carbon source? ? promoter deletion lactose-binding site mutation repressor DNA-binding site mutation operator deletion Suppose a scientist generates random mutations in E. coli and picks four strains to study. The scientist measures the protein level of B-galactosidase for each strain in the presence of different carbon sources, as shown in the table belovw Glycerol 0 100 100 0 Lactose Lactose and glucose Strain Wild type 100 Mutant 1 Mutant 2 Mutant 3 Mutant 4 100 100 0

Explanation / Answer

Promoter deletion
With out promoter there is no functional lac operon.

Mutant 1 = Repressor DNA binding site mutation
Mutant 2 = Operator deletion
Mutant 3 = Defective promoter CAP-cAMP binding site
Mutant 4 = Lactose binding site mutation

Mutant 1 and 2 are constitutive expression of lac operon.

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