Gene regulation governing lactose operon of E.coli that involves the lac I gene product is

Easy

A

positive and inducible because it can be induced by lactose.
B

negative and inducible because repressor protein prevents transcription.
C

negative and repressible because repressor protein prevents transcription.
D

feedback inhibition because excess of $β$ -galactosidase can switch off transcription.

Solution

The repressor of the lac operon is synthesised (all-the-time – constitutively) from the i gene. The repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon. Regulation of lac operon by repressor is referred to as negative regulation. In the presence of an inducer, such as lactose or allolactose, the repressor is inactivated by interaction with the inducer. This allows RNA polymerase access to the promoter and transcription proceeds.

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