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Biotechnology (continued) Immunology Genetic engineering has allowed for significant advances in the understanding of the structure and mode of action of antibody molecules. Practical use of immunological techniques is pervasive in biotechnology. Notably, antibodies are used in diagnostic procedures for detecting diseases of plants and animals, and in detecting minute amounts of materials such as toxic wastes, drugs, and pesticides. The antibodies themselves are being employed to target therapeutic agents to specific cellular sites. Antibodies are bivalent molecules that bind to their target molecules at one or both of their two combining sites. Hybrid antibodies are being produced in which one of the sites contains a drug or a poison, whereas the other site directs the antibody to its target, that is, a cancerous cell. The ability to artificially combine subunits of antibodies produced in differ- ent species also will tailor them for specific targets. In addition, antibodies are being developed with enzymatic properties, thereby enabling them to deactivate target molecules with which they combine in a cell. Monoclonal antibodies respond to a single antigenic site, allowing for great specificity. They have been most important in the diagnostic arena, where tests have been developed for human, plant, and animal diseases and for pregnancy and ovulation prediction. Agricultural science (plant and animal) Limited commercial products have been marketed for use in plant agriculture, but many have been tested. Interest has centered on producing plants that are tolerant to specific herbicides. This tolerance would allow crops to be sprayed with the particular herbicide, and only the weeds would be killed and not the genetically engineered crop species. Some herbicide-tolerant crop species have been isolated by selec- tion of tissue culture variants; in other cases, plants have been transformed with genes from bacteria that detoxify the herbicide. For example, a gene isolated from the soil bacterium Klebsiella pneumoniae ozaenae has been used to create plants that are resistant to the herbicide bromoxynil. Other strategies have been to alter plants so that they will overproduce the herbicide-sensitive biochemical target or so that the biochemi- cal target will be altered, thereby reducing the affinity of the herbicide for its biochemical target in the crop species. Tolerance to plant virus diseases has been induced in a number of crop species by transforming plants with portions of the viral genome, in particular the virus's coat protein and the replicase enzyme used for virus multiplication. Plants exhibiting this tolerance are available for commercial use once regulatory constraints are removed. Genes coding for protein toxins from the bacterium Bacillus thuringiensis have been introduced into a number of plant species to provide insect tolerance. Potato plants tolerant to the Colorado potato beetle and cotton plants tolerant to the cotton bollworm were the first commercial products of this technology. To enhance the quality and nutrition of foods, numerous techniques have been developed. Recombinant DNA strate- gies can be used to retard the softening of tomatoes, so they can reach the consumer with better flavor and keeping quali- ties. Another technique was developed to increase the starch content of the potato to enhance the quality of French-fried potatoes and potato chips, including reduction of their capac- ity to absorb oils during processing. With both selective plant breeding and genetic engineering, oil seed rape (also known as canola or Brassica napus) has been produced to yield plant- based oils (oleochemicals) for the specialty chemicals industry. Such oils are used to produce amides, fatty acids, esters, and other chemical intermediates. Oils high in erucic acid are used as lubricants and as additives to automatic transmission fluid. Oil seed rape is also an important source of oil for margarine production and cooking. Genetic engineering techniques can be used to lower the proportion of saturated fat by inserting the gene for the stearoyl–acyl carrier protein desaturase en- zyme into oil seed rape and other oil-producing crop plants. Biotechnology also holds great promise in the production of vaccines for use in maintaining the health of animals. However, because of the economics of the market, most emphasis has been placed on racehorses and pets, including cats and dogs. Subunit vaccines are being developed to replace live-virus or killed-whole-virus vaccines. Feline leukemia virus is an impor- tant disease, estimated to infect 1.5 million cats annually in the United States. Conventional vaccines are ineffective against the virus and may actually spread the disease. Subunit vaccines have been developed that overcome these disadvantages. Pseudorabies virus is the causal agent of an important disease affecting hogs. The conventional killed-virus vaccine gives only partial protection, and a live-virus vaccine is only slightly more effective. A genetically engineered vaccine has been developed in which the gene producing the enzyme that enables the virus to escape from nervous tissue has been deleted, thus reduc- ing virus virulence. Another vaccine incorporates genes for pseudorabies proteins into viable vaccinia virus as a vector to immunize animals. Recombinant vaccines are being produced for many other diseases, including foot-and-mouth virus and parvovirus. + ward ' s science