Let’s buy some. The plasmid we’ll buy confers resistance to the antibiotic ampicillin, and contains two EcoR1  restriction sites, outside the gene for resistance. Now, while we’re waiting for it to arrive, let’s cook up some synthetic DNA for a protein we’d like to make; insulin, say. We make this DNA up as a plasmid, too, with EcoR1 sites bracketing the insulin gene (Figure 16).

Now our package has arrived. We take the plasmid and treat it with EcoR1. We get a solution of linearized plasmids with sticky ends. We treat the insulin plasmid in the same way and mix them together. The sticky ends will cause these linearized plasmids to recombine in different ways, some of them useless for us. But some of the DNA plasmids will recombine with some of the resistance plasmids by joining their sticky ends. We add DNA ligase, which we met before during replication. DNA ligase seals the sticky ends together, making smooth, unbroken circles of recombinant DNA.

We now take our mixture of recombinant plasmids and add them to a broth containing swarms of commercially prepared E Coli bacteria. These E Coli were raised in the suburbs and went to parochial school on a voucher plan, so they’ve never been exposed to the evils of antibiotic resistance genes. They’d die if they even looked at ampicillin. Under the right conditions of salt concentration, growth medium and temperature, you can convince some of them to take up recombinant plasmids, just once, to see if they like it. Some of them get the useless plasmids, some of them get plasmids containing the resistance gene and the insulin gene, and some of them remember to Just Say No.

We now introduce all these punks to real life by adding ampicillin to the mixture. Those E Coli who failed to take up any plasmid, or who took up plasmids lacking the resistance gene, are cut off in the full flower of their youth. So much for clean living. We’re left with a culture of bacteria resistant to ampicillin and loaded with the gene for insulin. They divide, and their kids grow up just like them, packed with ampicillin resistance genes and the gene for insulin. We keep them alive in a vat; they work like dogs and make recombinant hormones for us. It’s a just and equitable arrangement, sort of a model for the Corporate Era.

Figure 27. Transfection of E. Coli With Recombinant DNA. Animated sequence. Keep watching.