How did an American Company. Eli Lilly use the knowledge of r-DNA technology to produce human insulin?

American Company Eli Lilly used the knowledge of r-DNA technology to produce human insulin in the following way.

1. Preparation of DNA corresponding to A and B chain separately
2. Extraction of plasmid from bacteria
3. Insertion of DNA corresponding to A and B chain separately in plasmid
4. Transforming the bacteria with this recombinant plasmid
5. Expression of the desired product from this DNA .
6. Purification of A and B chain
7. Linking them with disulfide bonds so that they act as human insulin