So instead of using prokaryotic cells to produce a desired eukaryotic protein, can we use eukaryotic cells, for example, animal cells, to actually produce copies of proteins that extract the proteins and use those proteins for a variety of different purposes? So it turns out that we can actually introduce recombinant DNA molecules, foreign DNA molecules, into certain eukaryotic cells, such as, for example, malcells, as we'll see in just a moment. And then these genes can basically use to express proteins, produce different types of proteins. Now, there are three methods that we normally use to basically inject a certain gene into a eukaryotic cell. Method number one, we'll call injection with microPET. Method number two, we're going to call injection with a viral agent, specifically with the retrovirus.