Question

You are studying an E. coli strain with the following genotype: I + P+ Oc Z- Y+ / F' I + P+ O+ Z+ Y-

The lacZ mutation is a nonsense mutation. Which statement best describes its mutant phenotype? a. It will produce ß-galactosidase and permease in the presence or absence of inducer. b. It will produce ß-galactosidase in the presence or absence of inducer but will never produce permease. c. It will produce permease in the presence or absence of inducer but will never produce ß-galactosidase . d. It will never produce ß-galactosidase or permease under any conditions.

Answer 1

Here Oc is operator constitutive. That's why permease enzyme is constitutive in nature. Because repressor can not bind to the operator. And allow RNA polymerase to bind to the promoter and provide constitutive synthesis of permease only because the DNA segment containing has Y+ only, there is Z-  

Now in presence of inducer, it will bind to the repressor and do not allow repressor to bind to operator. There will be synthesis of beta galactosidase occur from second strand. But in absence of inducer there is no synthesis of beta galactosidase.

Out of these options a option is more appropriate.

That's why right option is :

c. It will produce ß-galactosidase and permease in the presence or absence of inducer