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..~:he first fruits..` ........ Technicians inspect the control unit at the bottom of a large-scale evaporator used in the final steps of purifying human insulin produced by genetically engineered bacteria. ~2 . ............................................ ..... .............................. ............................................................ ~ ....................................................... ............................................... ............................................. . '''""""''"'''~ ....................................................... ............................................. ............... ~,~,.,.,, : 4=ts sms imnIar~ted contributed handsomely to human welfare in the few short years since they appeared. · Insulin, needed by millions of diabet- ics, has been produced commercially by genetically engineered bacteria since 1982. The product is identical to human insulin and so does not cause the allergic reactions sometimes produced by insulin derived from animals. Nor is its supply subject to the ups and downs of the livestock market. · Human growth hormone (HGH), needed for normal physical development, has been available as a genetically engi- neered product since 1985. Previously, many of the more than 10,000 U.S. children low in HGH could not get treatment with the natural substance, which is extracted in tiny amounts from the pituitary glands of cadavers at autopsy. And in 1985, distribu- lion of HGH from this source was stopped after evidence suggested it might be contam- inated with a virus causing a rare, fatal disease. Today, however, there is plenty of pure biosynthetic HGH. · Tissue-plasrruinogen activator, or t-PA, appeared as a genetically engineered product E N G ~ N E E R ~ N G A N D T H E A D VA N C E M E ~ 9~d ,.._, Do in late 1987. It quickly dissolves blood clots that cause heart attack and prevents their recurrence. It is already standard treatment for heart attack victims at hundreds of U.S. hospitals. These and other genetically engineered products now available are created through the efforts of biologists and engineers. It is biologists who "engineer" new organisms by splicing a gene from one organism into another. Traditional engineers provide an indispensable bridge from biology lab to the public. They design and build the mechani- cal systems that allow the new organisms to grow in large quantities and that process the valuable substances the organisms produce. In addition, they develop complex laboratory instruments that simplify and speed the work of genetic engineering. A genetically engineered product begins with biologists who find a gene that pro- duces a valuable substance such as HGH. Using enzymes that dissolve bonds to neighboring genes, they cut the valuable gene out of the DNA, the genetic material of a cell. Then they insert this gene into another organism such as the common bacterium Escherichia cold that will multiply itself and the foreign gene along with it. ! Once the genetically engineered "bug" has been created, engineers design a system in which its product can be produced and processed in large quantities at a reasonable cost. The production of human insulin, the first commercial product of genetic engineer ing, is a good example. It was developed in the United States and appeared commercial ly under the trade name Humulin, first in the T O F ~ U M ~ N W E ~ FA ~ E
United Kingdom and later in the United States. The insulin molecule is composed of two parts called A and B chains. The original Humulin process used two versions of E. cold t~ to produce the chains. One version contained a gene producing A chains and the other contained the B-chain gene. Each version was grown, or fermented, in a large separate tank. The chains they produced were extracted from the bacteria and purified. Afterward, A and B chains were combined in a third vessel. The complete molecules were then purified and crystallized into a usable form of human insulin. The Humulin process demanded special engineering to handle the uncertainty surrounding the first large-scale use of genetically engineered microbes. Scientists in the late 1970s did not know whether such bugs might survive in nature and contami- nate the environment. So the bacteria were grown in closed stainless steel tanks with the inflow of nutrients and oxygen carefully ! controlled by computer. Water vapor and carbon dioxide that flowed out were decon- taminated. A special double seal was invented to prevent the escape of microbes from around the shaft of the paddle-like agitator that stirred the culture. And the tanks were designed to function under negative pressure the opposite of conven- tional tanks to suck back any bacteria that otherwise might escape. Engineers also developed a new pasteurization system hot enough to kill the bacteria as they were withdrawn from the tanks, but cool enough not to damage the A or B chains. The big challenge In producing Humulir~, however, was in scaling up production from expensive 10-liter batches in the laboratory to less expensive batches of 40,000 liters ire the factory. The scaleup was particularly difficult because these bacteria store the A or B chains within themselves, unlike microbes that produce antibiotics and secrete them. Engineers devised a way to extract the chains by pressurizing the cells ire a tank and then shooting them out into no~.~al atmosphere, where the pressure change caused the cells to explode like balloons and release their contents. The G E N E T ~ C ~ ~ LY E N G ~ N E E R E D P R O D ~ C T S ~ 1 l Ill A spiraling chain of DNA, the genetic blueprint of life, shimmers in this computer- generated molecular model. Certain DNA segments malce up the genes that produce insulin, human growth hormones and other important so stances. 43
chains were separated from cell debris in several steps ending with high-performance liquid chromatography. This laboratory technique is perfo~`ed by pouring a mixture through a pencil-sized column of material that sifts out certain molecules. But for large- scale Humulin production, columns 10 feet tall and 12 to 16 inches in diameter had to be designed. Today, Humulin is produced by a The first insulin produced by bacteria implanted with human insulin genes was processed into crystals. The insulin must be separated from the bacteria and purified in relatively large quantities in order to be I useful to many diabetics. ~11__ _;~ _ , ::$:: #. ' :...'.''',..''' _ . ,~ · , ....' A.` .':'.- _:..:.:.:.-'' i. ~ - fir Potentially useful genes are often identified by analyzing the proteins they produce. A protein sequencer is used to determine the order of amino acids making up ~ chainlike protein molecule, thereby uncovering the identity of the gene that made it. 44 ,>..~.~ . ~ similar, but more efficient process involving a new type of genetically engineered bacteria and only one fermentation tank. Traditional engineers are not directly involved in some other aspects of genetic engineering, such as the genetic alteration of plants and animals or the potential treatment of humans with genetic disorders. They are, however, becoming more involved with processing the products that are produced by genetically altered plants and microorgan- isms. Biologists are modifying organisms to produce everything from pha~raceuticals to food processing agents to specialty chemi- cals. In fact, the greatest use of genetic engineering in the future may be in the I production of products that are now created by chemical processes, which often involve high temperatures and pressures as well as toxic by-products. Biological synthesis, on the other hand, usually takes place at room temperature under normal pressure and produces biodegradable waste. In the meantime, people have already begun to investigate the use of genetically altered microbes to clean up toxic waste, degrade pesticides, or to turn organic waste t material into useful products. They may one day use genetically altered bacteria to loosen underground oil so it can be pumped to the surface or to leach precious minerals from ore. Perhaps the biggest contribution of traditional engineering to this field has been the development of instruments that speed the process of genetic engineering and expand its possibilities. Two devices the protein sequencer and the DNA synthesizer- have already had tremendous impact on the detective work of genetic engineering. For instance, one biologist working with a DNA synthesizer can do the amount of work in one afternoon that would have taken 25 biologists five years to complete in the early 1970s. The discovery of a valuable gene often begins with identifying the sequence of amino acids in the protein it produces. There are only 20 different amino acids. But the chainlike protein molecules have hundreds of amino acids linked in specific order. An instrument that can decipher this sequence appeared on the market in 1969. It is essen- tially a computer-controlled plumbing device that uses solvents to cut one amino acid at a time from the end of a protein molecule. Knowing the amino acid order, biologists can identify the gene that made the protein. Another device, which entered the market in 1982, can actually build small genes or gene fragments out of DNA the genetic material found in cells. A DNA synthesizer hooks together subunits, called bases, in the proper order for a particular gene or gene fragment. These synthetic genes and fragments can then be used for several purposes, including genetic engineering. For example, the genes that produce Humulin are really synthetic genes created by a DNA synthesizer. The dream machine of genetic engineer- ing, though, is a device that can rapidly sequence DNA, much as proteins are sequenced. Human DNA contains more than 3 billion bases, and today's DNA sequencers can analyze only about 9,000 bases per day. The challenge for today's engineers is to develop in the next four or five years machines that are at least 10 times faster than present sequencers. The amount of genetic information already being generated by DNA sequencers is overwhelming. To check a new sequence against the massive, growing data bank of E N G I N E E R I N G Ji N D T H E A D VA N C E M E N T O F H U M A N W E L FA R E
known sequences will require faster comput- er systems. One under development uses a series of 500 or more microprocessors that can each be programmed to recognize one of the four types of DNA base. Essentially, the series is programmed to reflect the order of bases in the new DNA sequence. As known sequences from the data bank flow past the series, each microprocessor "lights up" when its particular base passes by. When all light up together, they signal the location of an identical sequence in the data stream. Using I this recognition system, the computer can search the DNA data bank for similar patterns thousands of times faster than existing computers. Work is under way to determine the entire sequence of human DNA, called the genome, and map the location of all 100,000 or so genes. This data would reveal more about human biology and disease than has been learned in the past 200 years. Scientists and engineers would dearly love to map the entire human genome. With the right tools, they may soon do it. Completing the project would be, some believe, the biological equivalent of putting a man or woman on the moon. G E N E T I C a L LY E N G ~ N E E R E ~ P R O D U C ~ S For nine years, a deficiency in human growth hormone tHGH, stunted the growth of this California girl. But in her tenth year, injections of HGH produced by genetically altered bacteria stimulated a 5-inch burst of growth, catching her nearly up to the normal height of a girl her age. 45