Practice question

Negative control architecture uses a repressor protein that reduces transcription when active. In lac context, lacI constitutively produces LacI repressor that occupies operator in lactose-free medium, establishing blocked state with transcription near zero. Release of negative regulator through inducer binding allows derepression. Conversely, positive regulation requires activator presence for additional stimulation beyond basal. CAP-cAMP enhances polymerase activity but does not repress, RNA polymerase is core machinery, and permease facilitates inducer import without directly contacting DNA regulatory elements. LacI therefore mediates negative regulation while CAP mediates positive regulation in this dual controlled operon.