The lac repressor binds to what site within the lac operon?

The lac repressor binds to what site within the lac operon?

• A. lacO
• B. lacZ
• C. promoter
• D. lacI

Answer: (A)

Regulation of the lac operon hinges on a repressor binding to the operator site. The Lac repressor recognizes and binds the operator DNA sequence, lacO, within the operon. When it is bound, RNA polymerase cannot effectively initiate transcription of the downstream genes lacZ, lacY, and lacA. In the presence of lactose, allolactose acts as an inducer that binds the repressor and causes it to release from lacO, lifting the block and allowing transcription to proceed. The promoter is simply the site where RNA polymerase binds to start transcription, not the site where the repressor binds. The lacI gene encodes the repressor itself, not the operator sequence.

Regulation of the lac operon hinges on a repressor binding to the operator site. The Lac repressor recognizes and binds the operator DNA sequence, lacO, within the operon. When it is bound, RNA polymerase cannot effectively initiate transcription of the downstream genes lacZ, lacY, and lacA. In the presence of lactose, allolactose acts as an inducer that binds the repressor and causes it to release from lacO, lifting the block and allowing transcription to proceed. The promoter is simply the site where RNA polymerase binds to start transcription, not the site where the repressor binds. The lacI gene encodes the repressor itself, not the operator sequence.