<prompt> Number of structural gene in Lac operon3456  <response>: Lactose operone or Lac operon The lac operon is a region of DNA in the genome of E. coli that contains following genetic elements ? i Three structural genes :- These code for 3 proteins that are involved in catabolism of lactose. These genes are Z gene codes for P-galactosidase, Y gene codes for galactoside permease, and A gene codes for thiogalactoside transacetylase. ii Regulatory gene lac i It produces repressor protein. iii A promotor site P :- It is the binding site for RNA polymerase. It contains two specific regions ? a CAP site Catabolite activator protein binding site. b RNA polymerase binding site iv An operator site 0 :- Repressor binds to this site and blocks transcription. 3 Structural genes are expressed only when 0 site is empty repressor is not bound and the CAP site is bound by a complex of cAMP and CAP catabolite gene activator protein. 