This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Biochemistry
The CAP cAMP regulator in Lac operon is known for which of the following functions? 
Select and explain. 
A. Positive regulator, B. Negative regulator, C. Constitutive expression, D. Attenuation
A: Positive regulator
Answer: A: Positive regulator 
Explanation: The CAP-cAMP regulator is acting as a positive regulator because its presence is required for gene expression. It functions in turning on the transcription of the structural genes in the operon. Ref:Harper's Illustrated Biochemistry 27thEdition, Page 80 - 384 ; Lippincotts Biochemistry 3rd Edition, Page 418, 419, 420 ; Principles of Genetics, 8th Ed By Gardner, Simmons, Snustad, 2006, Page 22.