Question

Explain why inactivation of the ${\text{O}}_{\text{1}}$sequence of the lac operator almost completely abolishes repression of the lac operon

Short answer

O1 sequences overlap the transcription start site, which once inactivated, doesn’t let the repressor bind to the site, thus abolishing the repression of the operon.

Step-by-step solution

Lac operon

The lactose operon, often called the lac operon, is a collection of genes present in E. coli and other bacteria that are dedicated to the absorption and processing of lactose.

Mechanism of the lac operon

The lac operon has three operator sequences to which lac repressor binds with high affinity, known as ${\text{O}}_{\text{1}}{\text{,O}}_{\text{2}}{\text{, andO}}_3$. is the primary repressor-binding site. It was identified through its protection by lac repressor from nuclease digestion.