Celebrating
100 Years
Nobel Laureates of AAI
Alfred Day Hershey, Ph.D.
(1908–1997)
Alfred D. Hershey, Ph.D., AAI ’42, was
awarded the 1969 Nobel Prize in Physiology or
Medicine jointly with Max Delbrück and Salvador E. Luria (AAI ’58) for “their discoveries
concerning the replication mechanism and the
genetic structure of viruses.”1 As leading figures in the study of viruses that infect bacteria,
known as bacteriophage, Hershey, Delbrück,
and Luria pioneered the fields of microbiology
and genetics. Hershey’s unique contribution
was the discovery that DNA, and not protein,
was the genetic material in bacteriophage, a
discovery based on evidence from the legendary
“blender experiment” undertaken with Martha
Chase in 1952.
Scientific Accomplishments
Bacteriophages were known to be comprised
of DNA and protein, and Hershey wanted to
determine which of these components was the
heritable material passed on to bacteria to form
bacteriophage progeny. To trace each of these
components separately, Hershey and Chase first
prepared one batch of bacteriophage with radioactive phosphorus to label DNA and another
with radioactive sulfur to label protein. They
then infected different bacterial batches with
each of these labeled bacteriophages. Using a
Waring blender to shear off the surface-attached
bacteriophage from infected bacteria, they were
able to analyze the radioactive content of the
bacteria and identify the transferred genetic
material.
Infected bacteria contained radioactive phosphorus and were also capable of producing
bacteriophage progeny, whereas radioactive sulfur was not associated with the bacterial DNA.
These results indicated that DNA was transferred from the bacteriophage to the bacteria
and that the genetic material in bacteriophage is
DNA. These observations enabled Hershey and
Chase to confirm that DNA, and not protein,
contained genetic information.2
Hershey next turned his attention to understanding the infection cycle of bacteriophage at
a molecular level and was the first to detect a
unique nucleic acid fraction that was later identified as messenger RNA.3 The consummate experimenter, Hershey continued to develop new
laboratory methods for handling, fractioning,
and measuring DNA. “There is nothing more
satisfying to me than developing a method,” he
once told a colleague. “Ideas come and go, but a
method lasts.”4
Hershey was renowned for his ingenuity in
the lab and was praised by molecular biologist
and geneticist Franklin W. Stahl, among other
titans, for being “fearless” in the laboratory and
“impeccable” in analysis. Stahl lauded Hershey
for his humility and absence of pretension: “He
talked to the reader, explaining things as he saw
Celebrating
100 Years
them, but never letting us forget that he was
transmitting provisional understanding. We got
no free rides, no revealed truths, no invitation
to surrender our own judgment. And we could
never skim, since every word was important.
I think this style reflected his verbal reticence,
which in turn mirrored his modesty.”5
Biography
Hershey was born on December 4, 1908, in
Owosso, Michigan. He attended Michigan State
College, where he earned his B.S. in 1930 and
his Ph.D. in bacteriology in 1934. His doctoral
dissertation examined the chemical makeup of
Brucella, the bacterium responsible for brucellosis.6 After completing his degree, Hershey
accepted a position as an instructor of bacteriology and immunology at Washington University School of Medicine in St. Louis, where he
worked closely with department head Jacques
Bronfenbrenner (AAI ’20, president 1942–46).
Since the early 1920s, Bronfenbrenner had focused his research on the physical and lysogenic
properties of bacteriophages, and he encouraged his new faculty member to begin studying
the viruses. During the late 1930s, Hershey and
Bronfenbrenner studied the growth of bacterial
cultures, but his own experiments in the early
1940s focused on the phage-antiphage immunologic reaction and other factors that influenced
phage infectivity.7 Looking back over them 60
years later, Stahl wrote that these studies “appear original, thoughtful, and quantitative,
especially those on the use of phage inactivation to permit the study of the antigen-antibody
reaction at ‘infinite’ dilution of antigen.”8
In late January 1943, Delbrück invited Hershey to Nashville to discuss his phage experiments with him and his close friend Luria.9
Together, the three formed the nucleus of the
“phage group,” an informal network of the
growing number of scientists devoted to studying the bacteriophage.10 In 1946, Hershey and
Delbrück, working independently, found that
different strains of bacteriophage can exchange
genetic material when both have infected the
same bacterial cell, creating a bacteriophage
that is a hybrid of the two, a process Hershey
referred to as genetic recombination.11 By the
mid-1940s, Hershey’s research with bacteriophage began to shift away from immunology to
genetics, biochemistry, and molecular biology.
In 1950, Hershey became a staff member
in the Department of Genetics of the Carnegie
Institution of Washington at the Cold Spring
Harbor Laboratory on Long Island. It was here
that he and Chase conducted the blender experiment. In 1962, Hershey was named head of the
Genetics Research Unit at Cold Spring Harbor,
a position he held until his retirement in 1972.
Hershey died on May 22, 1997, in Syosset,
New York, at the age of 88.
Awards and Honors
Hershey was a member of the National Academy of Sciences (1958) and the American Academy of Arts and Sciences (1959).
In addition to the Nobel Prize, he received the
Albert Lasker Basic Medical Research Award
(1958) and the Kimber Genetics Award (1965).
1 “Alfred D. Hershey—Biography,” Nobelprize.org, http://www.nobelprize.org/nobel_prizes/medicine/laureates/1969/hershey.
html.
2 A. D. Hershey and Martha Chase, “Independent Functions of Viral Protein and Nucleic Acid in Growth of Bacteriophage,” Journal
of General Physiology 36, no. 1 (1952): 39–56; A. D. Hershey and Martha Chase, “Genetic Recombination and Heterozygosis in
Bacteriophage,” Cold Spring Harbor Symposia on Quantitative Biology 16 (1952): 471–79.
3 “The Nobel Prize in Physiology or Medicine 1969—Press Release,” Nobelprize.org, http://www.nobelprize.org/nobel_prizes/
medicine/laureates/1969/press.html.
Celebrating
100 Years
4 Franklin W. Stahl, “Alfred Day Hershey, 1908–1997,” Biographical Memoirs (Washington, DC: National Academy of Sciences,
2001), 1–19, quote from 11.
5 Ibid., 12–13.
6 Ibid., 4.
7 Ibid.; A. D. Hershey, “The Absolute Rate of the Phage-Antiphage Reaction,” The Journal of Immunology 41, no. 3 (1941):
299–319.
8 Stahl, “Alfred Day Hershey,” 5.
9 Horace Freeland Judson, The Eighth Day of Creation: Makers of the Revolution in Biology, expanded ed. (Plainview, NY:
Cold Spring Harbor Laboratory Press, 1996), 35.
10 Ibid., 31.
11 Lawrence K. Altman, “Alfred D. Hershey, Nobel Laureate for DNA Work, Dies at 88,” New York Times, 24 May 1997, 26; A. D.
Hershey, “Spontaneous Mutations in Bacterial Viruses,” Cold Spring Harbor Symposia on Quantitative Biology 11 (1946): 67–77;
A. D. Hershey and Raquel Rotman, “Genetic Recombination between Host-Range and Plaque-Type Mutants of Bacteriophage in
Single Bacterial Cells,” Genetics 34, no. 1 (1949): 44–71.
Photo: Lasker Foundation