Eli Lilly company of America (1983) prepared two DNA sequences corresponding to A and B chains of human insulin and introduced them in plasmids of E. coli to produce insulin chains A and B. The extracted chains A and B were combined by creating disulfide bridges to produce functional insulin.
The insulin (proinsulin) manufactured by the functional human insulin gene contains polypeptide chain A, B and an extra stretch called the C peptide which is removed during maturation.
