The uses for genetically engineered products are in three categories: therapeutic, scientific, or agricultural. Therapeutic products are used for treating or pre venting disease. Therapeutic products sold today that have been derived from genetic engineering are the following:

 • hormones: epidermal growth factor, human growth hormone, insulin, relaxin, somatostatin

 • blood treatments: erythropoietin, factor VIII, prourokinase, streptokinase, tissue plasminogen activator

• cancer and chemotherapy products: alpha interferon, colony-stimulating factor, interleukins, taxol, tumor necrosis factor

• immunity affectors: interleukins, orthoclone and other monoclonal antibodies

• other disease treatments: beta-interferon for multiple sclerosis, gamma-interferon for granulomatous disease, pulmozyme for cystic fibrosis

• vaccines: hepatitis B, influenza

 The yeast Saccharomyces cerevisiae has become the most common microorganism engineered for producing many of the listed substances. Almost 100 percent of S. cerevisiae’s DNA has been sequenced— that is, scientists have identified the order of its base pairs—so this yeast has been the primary choice for gene manipulations. Other cell types that are genetically engineered to produce drugs are E. coli, Bacillus, Pichia pastoris yeast, and various mammalian cell lines.

Many therapeutic uses for genetically engineered substances go through a difficult process of DNA isolation and sequencing and development of high yielding clones. All new drugs must also be tested for safety and effectiveness in humans, a process called clinical testing. Tim Farley of the World Health Organization explained to BBC News, in 2005, the hurdles to overcome in developing a genetically engineered treatment for the acquired immunodeficiency syn drome (AIDS) virus. In this case, he discussed a genetically modified E. coli that would live in a person’s digestive tract—E. coli’s natural habitat—and secrete proteins that would enter the bloodstream and block infection by human immunodeficiency virus (HIV). “Clearly there are many steps to be completed in the development and clinical testing of the product,” he said, “and there may be special safety concerns over unexpected side effects due to deliberately colonizing [sic] the gastrointestinal tract with genetically engineered bacteria.” Ideas in genetic engineering for use inside and outside medicine have obstacles to overcome before their practical application.

Scientific applications in genetic engineering involve research on better and faster methods of DNA sequencing, screening for genes in microorganisms, developing accurate probes, developing efficient microbial producers, and perfecting analytical techniques. University laboratories also play a part in genetically engineered products by developing new methods for isolating, purifying, and cloning genes.

Agriculture has, for a long time, used the principles of genetic engineering for selecting plant lines that give better results than other plants. Some of the attributes that genetic engineering can deliver in plants are the following: bruise-resistant fruits, longer-shelf life fruits and vegetables, disease-resistant plants, natural insecticides, improved yields, drought resistance, freeze tolerance, longer growing season, and improved yields. Agricultural products made from genetically engineered microorganisms include the following:

• Pseudomonas bacteria that contain an insecticide gene from B. thuringiensis

• P. syringae, the ice-minus organism, which protects against ice formation on plants

• Rhizobium bacteria modified for enhanced nitrogen fixation

• herbicide-resistant plants containing bacterial genes

• livestock growth hormones produced by engineered E. coli

• cellulase enzyme made by engineered E. coli to make feeds more digestible

 • rennin enzyme made by the engineered mold Aspergillus niger for forming curds in dairy products

Agriculture will probably remain a major user of new genetically engineered plants, microorganisms, and even animals.

Genetic engineering might soon benefit the development of biologically produced fuels, called biofuels. Modified E. coli and other bacteria can be made to produce a diesellike fuel. Microorganisms engineered to produce fuels would benefit the environment by forestalling the depletion of fossil fuels and slow the destruction of forests now occurring for the production of plant-based biofuels.