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1941
George W. Beadle (1903-1989) and Edward L. Tatum (1909-1975) show how genes direct the synthesis of enzymes that control metabolic processes
Beadle, a geneticist, initially worked with the fruit fly Drosophila in the laboratory of Thomas Hunt Morgan at Columbia University. By 1935 he had developed suggestive evidence that eye color, known to be inherited, represents a series of genetically determined chemical reactions. His work over the next six years, much of it with Edward L. Tatum, a biochemist, furthered this hypothesis. But the complexity of Drosophila proved a drawback to developing experiments that would demonstrate a link between specific genes and their chemical products. In 1941, Beadle and Tatum turned to a simpler creature, in which specific products of metabolism could be directly studied. A bread mold, Neurospora crassa, proved ideal. Neurospora can be cultured together with sugar, inorganic salts, and the vitamin biotin. This fungus has a short life cycle, and reproduces sexually and replicates asexually—that is, sexual reproduction gives rise to spores. In addition, Neurospora possesses only one set of unpaired chromosomes, so that any mutation is immediately expressed. This much was known, mainly through the work of Bernard O. Dodge, when Beadle and Tatum began their research.
Normal products of this sexual recombination could multiply in a simple growth medium. However, Beadle and Tatum showed that some of the mutant spores would not replicate without addition of a specific amino acid—arginine. They developed four strains of arginine-dependent Neurospora—each of which, they showed, had lost use of a specific gene that ordinarily facilitates one particular enzyme necessary to the production of arginine. Beadle and Tatum's fairly simple experiment was a keystone in the development of molecular biology. In its basic form, the concept that genes produce enzymes had been first put forth as early as 1901 by Archibald Garrod—as Beadle acknowledged when he and Tatum were awarded the Nobel Prize in Physiology or Medicine in 1958. While Garrod's work had been largely ignored, Beadle and Tatum's research, more than three decades later, was immediately recognized. From Beadle and Tatum's work arose a basic hypothesis: One gene specifies the production of one enzyme. This idea was exceptionally fruitful, but also much debated and eventually modified. Today, it is usually said, more accurately, that each gene specifies the production of a single polypeptide—that is, a protein or protein component. Thus, two or more genes may contribute to the synthesis of a particular enzyme. In addition, some products of genes are not enzymes per se, but structural proteins.
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