In E. Coli, the gene laci codes the lac operon repressor. Which of the following statements is true about an E. coli strain, which is laci-, that is null mutant for laci.

a. There would be no lac operon repression, thus lacA, lacZ and lacY genes would be constitutively expressed regardless of the presence of lactose.

b. There would be no lac operon repression, thus lacA, lacZ and lacY genes would be expressed in the presence of lactose.

c. There would be no lac operon repression, thus lacA, lacZ and lacY genes would be constitutively expressed regardless of the presence of glucose.

d. There would be no lac operon repression, thus lacA, lacZ and lacY genes would be expressed in the presence of allolactose.

The correct answer will be option-A.

Explanation:

Lac operon is a set of genes arranged sequentially for lactose metabolism in E. coli. The lac operon gets activated in the presence of lactose as the lac operon consists of three enzyme coding genes called lacZ which codes for the β-galactosidase enzyme, lacY which codes for lactose permease, lacA which codes for acetyltransferase along with a regulatory gene called lacI which codes for repressor proteins.

The repressor proteins bind to the operator and control the transcription. When it binds to operator its huts off the transcription. If a mutation occurs in the laci gene then the protein will lose the machinery which will turn off the activity of enzymes and will lead to the constitutive expression of the genes irrespective of the inducer present or not.

Thus, option-A is the correct answer.