1953 - 1976: Expanding the Boundaries of DNA Research
The discovery of the structure of DNA resulted in an explosion
of research in molecular biology and genetics, paving the way for the
Nature magazine published
and Francis Crick's manuscript describing the double helix structure
Gey developed the HeLa human cell line.
Seymour Benzer at Purdue University devised an
experimental setup to map mutations within a short genetic region of a
particular bacterial virus. Over a five-year period, Benzer mapped
recombinations of genetic material that distinguished mutational
changes that had taken place at adjacent base pairs.
Heinz Fraenkel-Conrat took apart and reassembled the tobacco mosaic
virus, demonstrating "self assembly."
Francis Crick and George Gamov worked out the "central dogma,"
explaining how DNA functions to make protein. Their "sequence
hypothesis" posited that the DNA sequence specifies the amino acid
sequence in a protein. They also suggested that genetic information
flows only in one direction, from DNA to messenger RNA to protein, the
central concept of the central dogma.
Mexico became self-sufficient in wheat production for the first time
as a result of plant breeding efforts that began in 1943.
Matthew Meselson and Frank Stahl demonstrated the replication
mechanism of DNA.
Coenberg discovered and isolated DNA polymerase, which became the
first enzyme used to make DNA in a test tube.
The National Seed Storage Laboratory (NSSI) was opened in Fort
Collins, Colorado, becoming the first long-term seed storage facility
in the world.
Reinart regenerated plants from carrot callus culture.
Francois Jacob and Jacques Monod established the existence of genetic
regulation - mappable control functions located on the chromosome in
the DNA sequence - which they named the repressor and operon. They
also demonstrated the existence of proteins that have dual
Nikita Krushchev introduced hybrid corn to the Soviet Union after
visiting an Iowa corn farm belonging to Roswell Garst.
The steps in protein biosynthesis were delineated.
Systemic fungicides were developed.
The Rockefeller and Ford Foundation jointly established the first
international agricultural research center in cooperation with the
Philippine government and the International Rice Research Institute
Marshall Nirenberg built a strand of mRNA comprised only of the base
uracil. This strand is called "poly-u," and by examining it Nirenberg
discovered that UUU is the codon for phenylalanine. This was the
first step in cracking the genetic code, which Nirenberg and
colleagues succeeded in doing within five years.
UPOV, the International Union for the Protection of
New Varieties of Plants, is negotiated in Paris. The goal of the
"Convention of Paris" was to make uniform the enactment and
enforcement of Plant Breeders' Rights legislation around the world.
Watson and Crick shared the 1962 Nobel Prize for Physiology and
Medicine with Maurice Wilkins. Unfortunately,
whose work greatly contributed to the discovery of the double helical
structure of DNA, died before this date, and the Nobel Prize rules do
not allow a prize to be awarded posthumously.
The planting of high-yield wheat varieties (later known as Green
Revolution grains) began in Mexico. The seeds were released by the
Mexican Agricultural Program to other countries.
The FAO, backed by the U.N. Special Fund, established the Crop
Research and Introduction Center at Izanir, Turkey, for the study of
germplasm in that region.
Scientists noticed that genes conveying antibiotic resistance in
bacteria are often carried on small, supernumerary chromosomes called
plasmids. This observation led to the classification of the plasmids.
Harris and Watkins successfully fused mouse and human cells.
The genetic code was "cracked". Marshall Nirenberg, Heinrich Mathaei,
and Severo Ochoa demonstrated that a sequence of three nucleotide
bases (a codon) determines each of 20 amino acids.
conducted a study using one strand of natural viral DNA to assemble
5,300 nucleotide building blocks. Kornberg's Stanford group then
synthesized infectious viral DNA.
Mary Weiss and Howard Green took a crucial step in human gene mapping
with the publication of a technique for using human cells and mouse
cells grown together in one culture. This was called somatic-cell
Leonard Herzenberg, a geneticist at Stanford, developed the
fluorescence-activated cell sorter, which can identify up to 5,000
closely related animal cells.
Peter Duesberg and Peter Vogt, virologists at UCSF, discovered the
first oncogene in a virus. This SRC gene has since been implicated in
many human cancers.
Howard Temin and David Baltimore, working
independently, first isolated "reverse transcriptase" a restriction
enzyme that cuts DNA molecules at specific sites. Their work
described how viral RNA that infects a host bacteria uses this enzyme
to integrate its message into the host's DNA. This discovery allowed
scientists to create clones and observe their function.
Torbjorn Caspersson, L. Zech, and other colleagues in Sweden,
published the first method for staining human or other mammalian
chromosomes in such a way that banding patterns appear, like those
Painter found in the giant chromosomes of fruit flies nearly 40 years
Immunologist Hugh McDevitt, in an article in Science, reported
observing genes that control immune responses to foreign substances.
His observations suggested predictable, inherited susceptibility to
Paul Berg isolated and employed a
restriction enzyme to cut DNA. Berg used
ligase to paste two DNA strands together to form a hybrid circular
molecule. This was the first
The first successful DNA cloning experiments were performed in California.
In a letter to Science, Stanford biochemist Paul
Berg and others called for the National Institutes of Health to
enact guidelines for DNA splicing. Their letter recommended that
scientists stop doing certain types of recombinant DNA experiments
until questions of safety could be addressed. This letter was
provoked by experiments planned by Berg,
which had drawn vocal concern from the scientific community. Their
concerns eventually led to the 1975 Asilomar Conference.
Scientists for the first time successfully
transferred deoxyribonucleic acid (DNA) from one life form into
another. Stanley Cohen and Annie Chang of Stanford University and Herbert Boyer of UCSF
"spliced" sections of viral DNA and bacterial DNA with the same
restriction enzyme, creating a plasmid with dual antibiotic
resistance. They then spliced this recombinant DNA molecule into the
DNA of a bacteria, thereby producing the first recombinant DNA
Bruce Ames, a biochemist at UC Berkeley, developed a test to identify
chemicals that damage DNA. The Ames Test becomes a widely used method
to identify carcinogenic substances.
The first human-gene mapping conference took place. The conference
was inspired primarily by the rapid development in mapping by
The Proceedings of the National Academy of Sciences
published a paper by Stanford geneticist Stanley Cohen and UCSF
Boyer in which they demonstrated the expression of a foreign gene
implanted in bacteria by recombinant DNA methods. Cohen and Boyer showed that DNA
can be cut with restriction enzymes and reproduced by inserting the
recombinant DNA into Escherichia coli.
A moratorium on recombinant DNA experiments was called for at an
international meeting at Asilomar, California, where scientists urged
the government to adopt guidelines regulating recombinant DNA
experimentation. The scientists insisted on the development of "safe"
bacteria and plasmids that could not escape from the laboratory.
1975 Kohler and Milstein fused cells
together to produce monoclonal antibodies.
Herbert Boyer and
Robert Swanson founded Genentech, Inc., a biotechnology company
dedicated to developing and marketing products based on recombinant
J. Michael Bishop
and Harold Varmus,
virologists at UCSF, showed that oncogenes appear
on animal chromosomes, and alterations in their structure or
expression can result in cancerous growth.
The NIH released the first guidelines for recombinant DNA
experimentation. The guidelines restricted many categories of
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