What defines an operon, and how does lac operon regulation illustrate positive and negative control?

• A. An operon is a cluster of functionally related genes transcribed as a single mRNA under one promoter with an operator for repressor binding.
• B. An operon is a cluster of functionally related genes transcribed as a single mRNA under one promoter with an operator for repressor binding; lac operon demonstrates negative control by LacI and positive control by CAP-cAMP.
• C. An operon is a single gene regulated by multiple promoters.
• D. Lac operon is regulated only by positive control.

Answer: (B)