Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Tatum, Edward Lawrie

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from other bacteria, for example from the bacterium

Escherichia coli, do not function nearly as efficiently in the

polymerase chain reaction as the taq polymerase of Thermus

aquaticus.

Since the discovery of taq enzyme and the development

of the polymerase chain reaction, the importance of the

enzyme to molecular biology research and commercial appli-

cations of biotechnologyhave soared. Taq polymerase is

widely used in the molecular diagnosis of maladies and in

forensics (“DNA fingerprinting”). These and other applica-

tions of taq have spawned an industry worth hundreds of mil-

lions of dollars annually.

See alsoDNA (Deoxyribonucleic acid); DNA hybridization;

Extremophiles; Molecular biology and molecular genetics;

PCR

TTatum, Edward LawrieATUM, EDWARDLAWRIE(1909-1975)

American biochemist

Edward Lawrie Tatum’s experiments with simple organisms

demonstrated that cell processes can be studied as chemical

reactions and that such reactions are governed by genes. With

George Beadle, he offered conclusive proof in 1941 that each

biochemical reaction in the cell is controlled via a catalyzing

enzyme by a specific gene. The “one gene-one enzyme” the-

ory changed the face of biology and gave it a new chemical

expression. Tatum, collaborating with Joshua Lederberg,

demonstrated in 1947 that bacteriareproduce sexually, thus

introducing a new experimental organism into the study of

molecular genetics. Spurred by Tatum’s discoveries, other sci-

entists worked to understand the precise chemical nature of

the unit of heredity called the gene. This study culminated in

1953, with the description by James Watson and Francis Crick

of the structure of DNA. Tatum’s use of microorganismsand

laboratory mutationsfor the study of biochemical genetics led

directly to the biotechnologyrevolution of the 1980s. Tatum

and Beadle shared the 1958 Nobel Prize in physiology or med-

icine with Joshua Lederberg for ushering in the new era of

modern biology.

Tatum was born in Boulder, Colorado, to Arthur Lawrie

Tatum and Mabel Webb Tatum. He was the first of three chil-

dren. Tatum’s father held two degrees, an M.D. and a Ph.D. in

pharmacology. Edward’s mother was one of the first women to

graduate from the University of Colorado. As a boy, Edward

played the French horn and trumpet; his interest in music

lasted his whole life.

Tatum earned his A.B. degree in chemistry from the

University of Wisconsin in 1931, where his father had moved

the family in order to accept as position as professor in 1931.

In 1932, Tatum earned his master’s degree in microbiology.

Two years later, in 1934, he received a Ph.D. in biochemistry

for a dissertation on the cellular biochemistry and nutritional

needs of a bacterium. Understanding the biochemistry of

microorganisms such as bacteria, yeast, and molds would per-

sist at the heart of Tatum’s career.

In 1937, Tatum was appointed a research associate at

Stanford University in the department of biological sciences.

There he embarked on the Drosophila(fruit fly) project with

geneticist George Beadle, successfully determining that kynure-

nine was the enzyme responsible for the fly’s eye color, and that

it was controlled by one of the eye-pigment genes. This and

other observations led them to postulate several theories about

the relationship between genes and biochemical reactions. Yet,

the scientists realized that Drosophilawas not an ideal experi-

mental organism on which to continue their work.

Tatum and Beadle began searching for a suitable organ-

ism. After some discussion and a review of the literature, they

settled on a pink moldthat commonly grows on bread known

as Neurospora crassa.The advantages of working with

Neurosporawere many: it reproduced very quickly, its nutri-

tional needs and biochemical pathways were already well

known, and it had the useful capability of being able to repro-

duce both sexually and asexually. This last characteristic made

it possible to grow cultures that were genetically identical, and

also to grow cultures that were the result of a cross between

two different parent strains. With Neurospora,Tatum and

Beadle were ready to demonstrate the effect of genes on cel-

lular biochemistry.

The two scientists began their Neurosporaexperiments

in March 1941. At that time, scientists spoke of “genes” as the

units of heredity without fully understanding what a gene

might look like or how it might act. Although they realized

that genes were located on the chromosomes, they didn’t

know what the chemical nature of such a substance might be.

An understanding of DNA (deoxyribonucleic acid, the mole-

cule of heredity) was still 12 years in the future. Nevertheless,

geneticists in the 1940s had accepted Gregor Mendel’s work

with inheritance patterns in pea plants. Mendel’s theory, redis-

covered by three independent investigators in 1900, states that

an inherited characteristic is determined by the combination of

two hereditary units (genes), one each contributed by the

parental cells. A dominant gene is expressed even when it is

carried by only one of a pair of chromosomes, while a reces-

sive gene must be carried by both chromosomes to be

expressed. With Drosophila, Tatum and Beadle had taken

genetic mutants—flies that inherited a variant form of eye

color—and tried to work out the biochemical steps that led to

the abnormal eye color. Their goal was to identify the variant

enzyme, presumably governed by a single gene that controlled

the variant eye color. This proved technically difficult, and as

luck would have it, another lab announced the discovery of

kynurenine’s role before theirs did. With the Neurospora

experiments, they set out to prove their one gene-one enzyme

theory another way.

The two investigators began with biochemical

processes they understood well: the nutritional needs of

Neurospora. By exposing cultures of Neurosporato x rays,

they would cause genetic damage to some bread mold genes.

If their theory was right, and genes did indeed control bio-

chemical reactions, the genetically damaged strains of mold

would show changes in their ability to produce nutrients. If

supplied with some basic salts and sugars, normal Neurospora

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