Transfer of the Insulin gene into a plasmid vector. The plasmid is cut across both strands by a restriction enzyme , leaving loose, sticky ends to which DNA can be attached. Special linking sequences are added to the human cDNA so that it will fit precisely into the loose ends of the opened plasmid DNA ring. The plasmid containing the human gene, also called a recombinant plasmid, is now ready to be inserted into another organism, such as a bacterial cell. The recombinant plasmids and the bacterial cells are mixed up.
Plasmids enters the bacteria in a process called transfection.
With the recombinant DNA molecule successfully inserted into the bacterial host, another property of plasmids can be exploited - their capacity to replicate. Once inside a bacterium, the plasmid containing the human cDNA can multiply to yield several dozen copies. When the bacteria divide, the plasmids are divided between the two daughter cells and the plasmids continue to reproduce. Biology in Perspective. Biotechnology Industry Organization, 1990.