Which genetically modified organism is used for the commercial production of human insulin?

Why would the $lac Z$ gene be fused to the coding sequence of chain $A$ and $B$ in plasmids of $E. coli$?

When a gene is targeted to correct a disease by amplifying the gene,what is this process called?

In $1983$,Eli Lilly,an American company,first prepared two $DNA$ sequences corresponding to $A$ and $B$-chains of human insulin and introduced them into the plasmids of $Escherichia$ $coli$ to produce insulin chains. Chains $A$ and $B$ were prepared separately,extracted,and combined by creating:

What is a recombinant $DNA$ vaccine? Give two examples.

Mature insulin does not contain ........