Stanley Norman Cohen and Herbert Wayne Boyer pioneered techniques that now allow scientists to insert DNA from any source into bacteria and to detect the expression of the foreign genes in these simple cells.

Recombinant DNA (deoxyribonucleic acid) technology—known also in various guises as “genetic engineering,” “genetic modification,” and “gene cloning”—is an area of scientific investigation and applied biology that has, since its inception in 1973, revolutionized molecular biology, allowing scientists to address questions in cell biology that could not be addressed by earlier methods. Recombinant DNA methods allow molecular biologists to add one or a small number of genes from essentially any organism to simple bacterial cells. These foreign genes can be made to become an integral part of the bacterium, replicating along with the bacterial genetic material and thus stably transmitted from one bacterial generation to the next. The foreign genes can also be made to be functional in their bacterial host—that is, they can be induced to make their normal gene products. Genetic engineering
Recombinant DNA technology
[kw]Cohen and Boyer Develop Recombinant DNA Technology (1973)
[kw]Recombinant DNA Technology, Cohen and Boyer Develop (1973)
[kw]DNA Technology, Cohen and Boyer Develop Recombinant (1973)
[kw]Technology, Cohen and Boyer Develop Recombinant DNA (1973)
Genetic engineering
Recombinant DNA technology
[g]North America;1973: Cohen and Boyer Develop Recombinant DNA Technology[00960]
[g]United States;1973: Cohen and Boyer Develop Recombinant DNA Technology[00960]
[c]Science and technology;1973: Cohen and Boyer Develop Recombinant DNA Technology[00960]
[c]Biology;1973: Cohen and Boyer Develop Recombinant DNA Technology[00960]
[c]Chemistry;1973: Cohen and Boyer Develop Recombinant DNA Technology[00960]
Cohen, Stanley Norman
Boyer, Herbert Wayne
Berg, Paul
Smith, Hugh Oliver

Bacteria Bacteria, genetically altered are very simple single-celled organisms that are ubiquitous in nature. Although some are capable of causing disease, most bacteria are harmless to humans. Some, like the common intestinal bacterium Escherichia coli
Escherichia coli (E. coli), are normal inhabitants of the human body that are essential to human life. Each E. coli cell has a single circular DNA molecule, or chromosome, containing between two thousand and three thousand genes. In addition, some cells have one or more additional small circular DNA molecules called plasmids. Plasmids A typical plasmid contains on the order of five to ten genes and is therefore much smaller than the E. coli chromosome. These plasmids are semiautonomous, meaning that while they are incapable of leading a cell-free existence, they generally remain separate from the larger chromosome and control and direct their own replication and transmission to each daughter cell at cell division. Plasmids that contain genes for resistance to certain antibiotics, viruses, and so forth can provide the host cell with useful properties.

The “basic experiment” of recombinant DNA technology involves four essential elements: a method of generating pieces of DNA from different sources and splicing them back together; a “vector” molecule (often a plasmid) that can replicate both itself and any foreign DNA linked to it; a way to get this composite, or recombinant, DNA molecule back into a suitable bacterial host; and a means to separate those bacterial cells that have picked up the desired recombinant plasmid from those cells that have not.

As part of the process, the recombinant plasmids are then reintroduced back into E. coli host cells in a process called “transformation.” An essential feature of transformation is treatment of the host cells with calcium chloride, which weakens the cell walls and membranes, allowing the reconstituted plasmid DNA to be taken up inside the cells. If all has gone well, these genetically engineered clones of bacterial cells will then stably replicate the foreign DNA, along with the rest of the chromosomal and plasmid DNA of each cell generation; the products of the foreign genes—ribonucleic acid (RNA) RNA or protein—will be made as well.

By the early 1970’s, the stage was set for the advent of recombinant DNA technology. DNA “ligases” (enzymes that play a significant role in the process) had been discovered and purified independently in five separate laboratories in 1967. Hugh Oliver Smith described the first restriction endonuclease enzyme in 1970, and shortly thereafter Herbert Wayne Boyer described the isolation of EcoRI, a restriction endonuclease that became extremely important in the development of cloning methods. Paul Berg and his group described the construction of the first recombinant DNA molecules in a test tube, and at about the same time researchers in Stanley Norman Cohen’s laboratory reported on the first successful transformation experiments in E. coli.

In the fall of 1973, Cohen and Boyer were the first researchers to describe successful completion of a recombinant DNA experiment. Their report detailed the mixing and subsequent reconstitution of DNAs from two separate plasmids in E. coli. Shortly thereafter, they described experiments in which DNA from a plasmid found in an unrelated bacterium was successfully cloned in E. coli, and one year later they reported on the first successful cloning of animal genes in E. coli.

Recombinant DNA technology is widely considered to be the most significant advance in molecular biology since the elucidation of the molecular structure of DNA in 1953 by biophysicists James D. Watson Watson, James D. and Francis Crick. Crick, Francis It soon became apparent, however, that the technology had opened a Pandora’s box of social, ethical, Bioethics;recombinant DNA technology
Ethics;genetic engineering and political issues unprecedented in scientific history. The research held the potential of addressing biological problems of fundamental theoretical and practical importance, yet it generated real concerns also, because some experiments might present new and unacceptable dangers. Even in the course of scholarly research with the best intentions, there was concern that a laboratory accident or an unanticipated experimental result might introduce dangerous genes into the environment, with E. coli carrying them.

Soon after the scientific concerns were first voiced, a conference was planned to allow many of the leading researchers in molecular biology to try to assess the potential dangers of recombinant DNA technology. The conference was held at the Asilomar Conference Asilomar Conference (1975) Center in February of 1975. Six months earlier, however, eleven respected authorities in molecular biology, including Cohen, Boyer, Berg, and others who helped develop recombinant DNA techniques, signed a letter that was simultaneously published in three English and American scientific journals. This letter called for a voluntary moratorium on recombinant DNA experiments until questions about potential hazards could be resolved. The development of a set of guidelines for recombinant DNA research, a modification of which was later adopted by the National Institutes of Health, was discussed at the Asilomar Conference. Levels of both biological and physical “containment” were defined, and each type of recombinant DNA experiment was assigned to an appropriate level. Some types of experiments were banned. In the years that followed the initial furor, guidelines have been modified accordingly, as many of the initial fears about possible dangers have proved to be groundless.

As predicted, recombinant DNA technology has proved to have extensive practical applications, particularly in the fields of medicine and agriculture. Virtually all insulin-dependent diabetics now take human insulin Insulin;genetically engineered made by genetically engineered bacteria. Human growth hormone, prolactin, interferon, and other human gene Gene therapies products with specific therapeutic uses in medicine are available only because they can be made in quantity by using cloning. In agriculture, improved species of genetically modified crop plants have been designed to help address problems in global food supplies. Genetic engineering;agriculture Of particular note is the effort to clone the bacterial genes for nitrogen fixation into crop plants, thus obviating the need for most fertilizers. Genetic engineering
Recombinant DNA technology

• Cohen, Stanley N. “The Manipulation of Genes.” Scientific American 233 (July, 1975): 24-33. Eminently readable and profusely illustrated, this article provides the general reader with an excellent historical perspective on the development of recombinant DNA technology and a sound description of the scientific processes involved. Discussion of the use of plasmids as vectors is particularly useful.
• Drlica, Karl. Understanding DNA and Gene Cloning: A Guide for the Curious. 4th ed. New York: John Wiley & Sons, 2004. A good introduction to the impact of DNA technology on human lives.
• Fredrickson, Donald S. The Recombinant DNA Controversy: A Memoir—Science, Politics, and the Public Interest, 1974-1981. 2d ed. Washington, D.C.: ASM Press, 2001. The author, National Institutes of Health director from 1975 to 1981, offers a glimpse into the heated controversy surrounding the new technology.
• Grobstein, Clifford. “The Recombinant-DNA Debate.” Scientific American 237 (July, 1977): 22-33. Written at the height of the public controversy over the risks and benefits of recombinant DNA research, this thoughtful article provides a unique perspective to the history of the phenomenon. Colorful, helpful illustrations complement Grobstein’s balanced treatment of the sensitive issues.
• Jackson, David A., and Stephen R. Stich, eds. The Recombinant DNA Debate. Englewood Cliffs, N.J.: Prentice-Hall, 1979. A collection of seventeen essays, written by recognized leaders in the fields of molecular biology, ethics, and philosophy, covering all aspects of the controversy. Of particular note are essays by Robert L. Sinsheimer and George Wald, two of the most vocal scientists who pushed for a halt to recombinant DNA research.
• Knowles, Richard V. Genetics, Society, and Decisions. Columbus, Ohio: Charles E. Merrill, 1985. This broad-based college text was written for nonbiology majors with an interest in science and the social issues raised by the new advances in biology. Good treatment of basic principles of genetics, particularly as applied to humans. Chapter 19 provides a straightforward presentation of recombinant DNA, including the relevant science, history, applications, and controversial issues. Many useful illustrations.
• Vigue, Charles L., and William G. Stanziale. “Recombinant DNA: History of the Controversy.” American Biology Teacher 41 (November, 1979): 480-491. Written primarily for teachers of secondary school biology, this short article summarizes the history and controversy surrounding the recombinant DNA debate. Should be readily accessible to the average reader and a good first choice for further reading.

Berg, Gilbert, and Sanger Develop Techniques for Genetic Engineering

Cech Demonstrates That RNA Can Act as an Enzyme

Murray and Szostak Create the First Artificial Chromosome

Jeffreys Discovers the Technique of Genetic Fingerprinting

Erlich Develops DNA Fingerprinting from a Single Hair