Number of structural gene in Lac operon
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).
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