Alfred Day Hershey


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(1908–1997) American biologist

Hershey was born in Owosso, Michigan, and graduated from Michigan State College in 1930, remaining there to do his PhD thesis on the chemistry of Brucella bacteria. Having received his doctorate in 1934, he taught at Washington University, St. Louis, until 1950, when he moved to the Genetics Research Unit of the Carnegie Institute, Washington. In 1962 he became director of the unit, a position he retained until his retirement in 1974.

Hershey, along with Salvador Luria and Max Delbrück, was one of the founders in the early 1940s of the so-called ‘phage group’. In 1945, independently of Luria, he demonstrated that spontaneous mutations must occur in bacterial viruses (phage). In the following year he established, at the same time as Delbrück, that genetic recombination takes place between phages present in the same cell.

Hershey is best known, however, for the experiment conducted with Martha Chase and reported in their 1952 paper, Independent Functions of Viral Proteins and Nucleic Acid in Growth of Bacteriophage. At the time it was still uncertain whether genes were composed of protein, nucleic acid, or some complex mixture of the two. They utilized the fact that DNA contains phosphorus but no sulfur, while phage protein has some sulfur in its structure but no phosphorus. Phage with a protein coat labeled with radioactive sulfur and DNA with radioactive phosphorus was allowed to infect bacteria. After infection the bacteria were spun in a blender. The labeled protein was stripped off the bacteria while the radioactive DNA remained inside the bacterial cell. When allowed to incubate, the bacteria proved capable of producing a new phage crop. The experiment would seem to show that DNA was more involved than protein in the process of replication.

For his fundamental contributions to molecular biology, Hershey received the 1958 Albert Lasker Award and the 1965 Kimber Genetics Award. However, it was not until 1969 that Hershey, together with Delbrück and Luria, was awarded the Nobel Prize for physiology or medicine.

Subjects: Science and Mathematics.

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