an introduction to biotech

1. Genetic engineering using living organisms was first accomplished soon after it became feasible in the early
1970s. In 1973 Herbert Boyer, of the University of California at San Francisco, and Stanley Cohen, at Stanford
University, reported the construction of functionalorganisms that combined and replicated genetic information
from different species. Their experiments dramatically demonstrated the potential impact of DNA recombinant
engineering on medicine and pharmacology, industry and agriculture.
Boyer and Cohen's achievement represented an advance upon the ingenious
techniques developed by Paul Berg, in 1972, for inserting viral DNA into
bacterial DNA. It was a creative synthesis of earlier research that made use of:
• Living organisms able to serve as carriers for genes from another organism.
• Enzymes to cleave and rejoin DNA fragments that contain such genes.
• DNA molecules from one organism precisely targeted and manipulated for
insertion into the DNA of another organism.
Boyer and Cohen, both biochemists, recognized the complementary nature of
their work in 1972. Cohen's research involved plasmids—the nonchromosomal,
circular units of DNA found in, and sometimes exchanged by, bacteria. Boyer
was working on restriction enzymes, produced by bacteria to counter invasion
by viral organisms known as bacteriophages. In general, restriction enzymes
and plasmids are both part of natural systems of defense evolved by bacteria;
both, when Boyer and Cohen began to work together, were recent discoveries.
In 1970 Cohen found a way in which E. coli could be made to acquire a
plasmid, known as pSC101, that conferred resistance to the antibiotic
tetracycline. Together, Boyer and Cohen discovered that an
enzyme, Eco RI, would cleave the circular plasmid at a single site. Into the
breach they inserted a gene that provided resistance to another antibiotic,
kanamycin. They then repaired the plasmid. Subsequent colonies of E.
coli included bacteria that were resistant both to tetracycline and to
kanamycin.
Boyer and Cohen repeated the basic recombination in other ways, using a
plasmid from another species of bacteria, for example. But most
significantly, they also introduced genes from the toad Xenopus laevis into
bacteria, demonstrating that these genes were active in generation after
generation of E. coli. Bacteria, which replicate every twenty minutes, could
in principle be employed on a large scale to manufacture the products of
genes from higher animals, which reproduce much less frequently. Genes
and gene products could be produced rapidly and in quantity.
The demonstration of recombinant DNA represented a watershed in a long
series of advances in molecular genetics and biochemistry. Within several years, enhanced by new techniques
for mapping and rapidly sequencing genes, genetic engineering became the basis for an explosion in
biotechnology that continues unabated to the present.
Herbert Boyer
Courtesy Genetech
Stanley N. Cohen