At Stanford, Tatum and Beadle used X rays to induce mutations in strains of the pink bread mold Neurospora crassa. They found that some of the mutants lost the ability to produce an essential amino acid or vitamin. Tatum and Beadle then crossed these strains with normal strains of the mold and found that their offspring inherited the metabolic defect as a recessive trait, thereby proving that the mutations were in fact genetic defects. Their research showed that when a genetic mutation can be shown to affect a specific chemical reaction, the enzyme catalyzing that reaction will be altered or missing. Thus, they showed that each gene in some way determines the structure of a specific enzyme (the one-gene--one-enzyme hypothesis).
As a professor at Yale University (1945-48), Tatum successfully applied his methods of inducing mutations and studying biochemical processes in Neurospora to bacteria. With Lederberg, he discovered the occurrence of genetic recombination, or "sex," between Escherichia coli bacteria of the K-12 strain. Largely because of their efforts, bacteria became the primary source of information concerning the genetic control of biochemical processes in the cell.
Tatum returned to Stanford in 1948 and joined the staff of the Rockefeller
Institute for Medical Research (now Rockefeller University), New York
City, in 1957.
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