Gene regulation governing lactose operon of E.coli that involves the lac I gene product is Negative and repressible because repressor protein prevents transcription; Feedback inhibition because excess of β-galactosidase can switch off transcription; Negative and inducible because repressor protein prevents transcription; Positive and inducible because it can be induced by lactose

In negative inducible operons, a regulatory repressor protein is normally bound to the operator, which prevents the transcription of the genes in the operon. If an inducer molecule is present, it binds to the repressor and changes its conformation so that it is unable to bind to the operator. This allows for expression of the operon. The lac operon is a negatively controlled inducible operon, where the inducer molecule is allolactose.