How is E.coli used to produce human insulin?

E.coli can be used to produce human insulin in the following way.
1. Gene encoding for the production of insulin in humans is isolated. Like the gene for two insulin chain A and B are isolated.
2. The desired genes are introduced in plasmids of  two E.coli.
3. Since the plasmid is self replicating the introduced gene is expressed and the two chains A and B are formed separately. 
4. These chains are extracted
5. They are joined by creating disulfide bonds to form insulin.