A. Making a Gene Product Essay Example for Free

A. Making a Gene Product Essay We have just seen that one way of identifying cells carrying a particular gene is by assaying for the gene product. Such products are themselves, of course, a frequent objective of genetic engineering. Most of the earliest work in genetic engineering made use of E. coli to synthesize the gene products. E. coli has the advantage that researchers are very familiar with this easily grown organism and with its genetics. It also has several disadvantages. Like other gram-negative bacteria, it produces endotoxins as part of its outer layer. Since endotoxins cause fever and shock in animals, their accidental presence in products intended for use in humans would be in a serious problem. Another disadvantage of E. coli is that it does not usually secrete protein products. To obtain a product, cells must usually be broken open and the product purified from the resulting â€Å"soup† of cell components (Barton, 2000). Recovering the product from such a mixture is expensive when done on an industrial scale. It is more economical to have an organism secrete the product so that it can be recovered continuously from the growth medium. One approach has been to link the product to a natural E. coli protein that the bacterium does secrete. This approach has been used to produce insulin. Certain gram-positive bacteria, such as Bacillus subtilis, are more likely to secrete their products and are often preferred industrially for that reason. Another microbe that shows promise as a vehicle for the expression of genetically engineered genes is baker’s yeast, Saccharomyces cerevisiae. Its genome is only about four times larger than that of E. coli and is probably the best understood eukaryotic genome. Yeasts may carry plasmids; their cell walls can readily be removed to introduce plasmids carrying engineered genes. As eukaryotic cells, yeasts may be more successful in expressing foreign eukaryotic genes than bacteria. Furthermore, yeasts are likely to continuously secrete the product. Because of all these factors, yeasts have become the workhorse of eukaryotic cells. Yeasts also have a psychological advantage in the marketplace. Bacteria and viruses are, unfairly, associated in the public’s mind with diseases, whereas yeasts have a much more benign image, thanks to their association with baking, brewing, and wine-making (Barton, 2000). Animal viruses have also been used in making engineered gene products, primarily in the field of vaccine production. For example, scientists have been able to insert genes for the surface proteins of pathogenic microbes into the generally harmless vaccinia virus. The result is a sort of â€Å"sheep in wolf’s clothing,† a virus that has the external proteins of a pathogen but dies not cause disease. When an animal host is infected with the engineered virus, the host’s immune system recognizes these proteins as foreign and, in response, develops an immunity that can protect it against the actual pathogen. Because the vaccinia virus is unusually large and has room for several extra genes, a genetically engineered vaccinia virus might theoretically be used as a vaccine for several diseases simultaneously (Weaver, 2004). Mammalian cells in culture, even human cells, can be used much like bacteria to produce genetically engineered products. Scientists have developed effective methods for growing mammalian cells in culture as hosts for growing viruses. In genetic engineering, mammalian cells are often the best suited to make protein products for medical use; these products include hormones, lymphokines (which regulate cells of the immune system), and interferon (a natural antiviral substance that is also used to treat some cancers) (Anderson Diacumakos, 2001). While plant cells can also be grown in culture, altered by recombinant-DNA techniques, and then used to generate genetically engineered plants. Such plants may prove useful as sources of valuable plant products, such as alkaloids (the painkiller codeine, fro example) and the isoprenoids that are the basis of synthetic rubber.