This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Molecular Genetics, Subject name: Biochemistry
False statement is: 
Select and explain. 
A. Repressor binds operator gene, B. Regulator genes produce repressor subunits, C. IPTG is inducer but not substrate, D. Regulator gene is inducible
D: Regulator gene is inducible
Answer: D: Regulator gene is inducible 
Explanation: Ans. D. Regulator gene inducible(Ref: Harper 31/e page 412)Structural genes are inducible, not the regulator genes.Lac I gene produces Repressor subunits.IPTG is an inducer of lac-operon, but itself is not a substrate. This is called gratuitous inducer.