A lacI mutant
An E. coli mutant cannot make a functional lac repressor (lacI⁻). How are its lac genes expressed?
Answer D: explanation for every choice
A
Lactose dependence requires a functional repressor.
B
The genes are transcribed because nothing blocks the operator.
C
Glucose actually lowers lac expression by reducing cAMP–CAP activation.
D
Correct. With no repressor to bind the operator, transcription happens regardless of lactose.
TakeawayNo functional repressor → constitutive expression.
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Reviewed 2026-11-05 by a medical student. Spot an error? Report it with question ID bb134.