In 1983, the American company Eli Lilly successfully used the bacterium Escherichia coli to produce human insulin. What was the exact nature of the genetic material introduced into the plasmids of this host organism?

Step-by-step solution

In 1983, Eli Lilly prepared two DNA sequences corresponding to the A and B chains of human insulin and introduced them into plasmids of Escherichia coli to produce insulin chains. A single DNA sequence for proinsulin was not used because bacteria lack the enzymes required to remove the C-peptide and process proinsulin into mature insulin. The C-peptide itself is not part of mature insulin, so its sequence alone would not yield the functional hormone. Direct insertion of mRNA is incorrect because mRNA must first be