Genetic Engineering, Part II

After the discovery of methods for making recombinant DNA, the second major advance that led to the current revolution in genetic engineering was to develop the ability to introduce DNA from one organism into another, creating what we call transgenic organisms. This may sound like a difficult thing to do, like creating a genetic Frankenstein monster. It isn’t so, however.

To understand this we need some background in a process called conjugation. Conjugation occurs when one bacterial cell forms a physical connection to other bacteria cell, and then transfers a small piece of DNA called a plasmid. Some biologists say it is something like sex between bacteria. Using recombinant DNA technology to modify the DNA in a bacterial plasmid, say by inserting a gene from another organism, we can use conjugation to transfer it into other bacterial cell.

Let’s say we want to insert a gene from a firefly into a bacterial cell. Let’s say we want to insert the gene for the enzyme luciferase, which is the enzyme responsible for making the firefly’s tail light up. Why would we want to do this? Well, for a couple of reasons maybe. We might want to insert a gene into the bacteria so we can make a lot of copies of that gene, which we would need to do if we wanted to study the structure of that gene. Alternatively, we might do that because we want to make a lot of copies of the protein produced by that gene, and it is a lot easier to make a lot of the protein using bacteria as opposed to raising fireflies.

To do this we need to get the firefly’s luciferase gene into e. coli bacteria using a restriction enzyme that would clip out the gene from the firefly’s genome, and also make a single cut in a bacterial plasmid piece of DNA. If we can find the right restriction enzyme to do this, and it is very likely we can because these restriction enzymes recognize so many kinds of sites, we can use the enzyme to cut bacterial plasmids and the firefly’s genome. Then we recombine the gene from the firefly with the plasmid using the sticky ends of both.

Once again, to get this process to work, there are more details we need to pay attention to. For example, we need to make sure that we’re actually putting in the right piece of DNA from the firefly. We also need to figure out ways to identify the particular bacteria that had taken up the recombinant plasmid. There is a wide array of techniques used in this area.

Other methods to make transgenic organisms involve genetically engineering small chromosomes that not only have the regions of DNA we’re interested in, but also all of the other regulatory DNA and other factors that are associated with normal chromosomes. These chromosomes can be replicated and function like normal chromosomes in the cell. For example, there has been great success in creating an artificial yeast chromosome. Yeasts are very simple eukaryotes. So, we can put artificial chromosomes with whatever genes we want into yeast cells very conveniently. There has been in fact considerable success in making a functional artificial human chromosome.

The technical challenges associated creating a transgenic organism do become increasingly difficult the more complex the host organism we want to manipulate. However, it won’t be very long before it comes routine to insert foreign DNA into any kind of cell.