An E. coli mutant has a lacI gene producing a repressor that cannot bind allolactose. In glucose-free medium with lactose present, what happens to lac operon expression?
- A
Operon is induced via a separate cAMP-CAP-only mechanism
- Bcheck_circle
Repressor stays bound to operator → lac operon stays OFF despite lactose
- C
Operon is constitutively ON because repressor cannot function
- D
Operon is normally regulated because allolactose binding is unnecessary
Explanation
Allolactose normally binds the repressor and releases it from the operator. A repressor that can't bind allolactose remains stuck on the operator — operon stays repressed (super-repressor / lacI-s phenotype).