The rDNA technique of production of human insulin involves inserting the human insulin gene and the promoter gene of lac operon in the plasmids of E.coli.
The genes for insulin A and B chains are separately inserted into the plasmid of two different E.coli cultures. The lac operon system is used to express both the genes. The E.coli cells are cultured in a medium containing lactose which induces the synthesis of both the chains. The insulin chains so obtained can be isolated, purified and joined together to give human insulin. Human insulin is marketed under the brand name ’Humulin’.