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#717 - Biotech: The Basics -- Part 2, 31-Jan-2001

by Rachel Massey*

In the last issue, we looked at hazards associated with eating
genetically engineered foods: unexpected allergic reactions;
unexpected toxicity; and the development of antibiotic
resistance.[1] It is increasingly clear that genetic engineering
is neither precise nor predictable; "genetic engineers" are
tampering with the instructions for basic cell functions, without
understanding fully how those instructions work.

** One source of unpredictable effects is the use of "promoter"
genes. As we saw in REHN #716, the aim of genetic engineering is
to take a gene from one organism and insert it into another
organism. However, organisms have elaborate defense mechanisms to
prevent foreign genes from affecting them, so a gene moved from a
bacterium to a plant will not automatically work in its new host.
To overcome the target organism's defenses and make the new gene
function, it is necessary to add a "promoter" gene -- a genetic
switch that "turns on" the foreign gene.

The promoter of choice in most cases is derived from a plant
virus called the cauliflower mosaic virus. Known as the CaMV 35S
promoter, this genetic sequence causes hyperexpression of other
genes. A gene is hyperexpressed when the proteins for which it
contains instructions are produced in excessive amounts --perhaps ten
to a thousand times as great as normal levels.
Because the CaMV 35S gene is so powerful, in addition to "turning
on" the target gene, it may also "turn on" other genes near where
it is inserted, causing the engineered cell to display
unpredictable new features.[2]

** Plants can defend themselves against the intrusion of foreign
genetic instructions through the phenomenon of "gene silencing,"
in which the cell blocks expression of the foreign DNA. Silencing
may occur in unpredictable ways in genetically engineered plants.
For example, a recent study found that infection with the
cauliflower mosaic virus could trigger silencing of a newly
inserted trait for herbicide tolerance, which was linked to the
CaMV 35S promoter. Apparently, the plant defended itself against
the infection through silencing of the viral genes. At the same
time, it silenced other newly-inserted genes.[3]

** Genetically engineered foods may also produce unexplained
health effects in laboratory animals. An article published in THE
LANCET by Stanley Ewen and Arpad Pusztai reports on a study of
laboratory rats fed genetically engineered potatoes.[4] The
potatoes were designed to produce a substance known as GALANTHUS
NIVALIS agglutinin (GNA), which is ordinarily found in snowdrops
(a type of flower). The purpose of adding GNA to potatoes was to
increase resistance to certain insects and other pests.

Ewen and Pusztai worked with three groups of rats. One received
the genetically engineered potatoes designed to produce GNA; the
second received ordinary, non-engineered potatoes, without GNA;
and the third group received ordinary, non-engineered potatoes
mixed with a dose of GNA. Ewen and Pusztai studied the changes
that occurred in the digestive systems of the rats in each group.

The researchers found that eating engineered or non-engineered
potatoes with GNA was associated with certain changes in the
rats' stomachs. In addition, the engineered GNA potatoes were
associated with certain intestinal changes NOT found in the rats
fed ordinary potatoes laced with GNA. The researchers do not know
the reason for these additional changes. They could be due to a
"positioning effect" -- the foreign gene may have been inserted
at a location in the existing genetic material that caused it to
disrupt normal functioning of an existing gene. Or it could be
due to the activity of other genetic material inserted along with
the target gene, such as the promoter.

Pusztai was forced to retire from his research position at the
Rowett Research Institute in Scotland after he spoke publicly
about the results of his work. (See REHN #649.) His article in
THE LANCET is one of only a few animal feeding studies that have
been published on the altered foods that are now present,
unlabeled, in our grocery stores.

** In some cases, genetically engineered crops can have altered
nutritional content. One study found that glyphosate-tolerant
soybeans had significantly altered levels of naturally occurring
compounds known as isoflavones, which are thought to have some
health benefits.[5] The consequences of changes like this could
be minor in some cases and serious in others. The important
lesson is that when we eat soy, corn, or other important foods
that have been genetically altered, we may not be getting the
nutrient mix we could expect in the past. As long as these
altered foods are unlabeled, we do not have the information we
need to make informed choices about the foods we eat.

Last fall, corn products in U.S. supermarkets were found to be
contaminated with "StarLink" corn, a genetically engineered
variety approved only for use as animal feed due to concerns
about possible allergic reactions in humans.[6] The contamination
was detected by a non-governmental organization, Friends of the
Earth, working as part of a national collaborative effort, the
Genetically Engineered Food Alert coalition. Had Friends of the
Earth not taken responsibility for testing foods -- a function
that should be performed by government -- we could have continued
to consume unapproved StarLink corn with no way to trace the
health consequences. We do not know what other errors may already
have occurred; and since we do not know when we are eating
genetically engineered foods, we have no way to watch for links
between eating these foods and developing certain illnesses.
Those who favor the rapid and unregulated introduction of
genetically engineered foods into our food supply often say
genetic engineering is really nothing new; it is simply an
extension of conventional agricultural breeding techniques. In
fact, as Michael Hansen of Consumers Union explains in a review
article, there are some obvious differences.[2]

** Gene transfers across natural boundaries: Conventional
breeding transfers genetic information among organisms that are
related to one another -- members of the same species, or related
species, or (rarely) of closely-related genera. (Genera is the
plural of genus; a genus is a biological grouping that includes
multiple species.) Genetic engineering, on the other hand, may
transfer genes from any organism to any other organism (fish to
fruit, bacteria to vegetables, etc.).

** Location of gene insertion: Variations of a gene are known as
alleles. Genes are carried in chromosomes, and each gene has a
specific place in a chromosome. Conventional breeding shuffles
alleles of existing genes. In general, conventional breeding does
not move genes from one place to another in a chromosome. Genetic
engineering, on the other hand, inserts genes that were not in
the original chromosome of the target organism. These genes may
be inserted in unpredictable locations in the chromosome,
producing unforseeable changes in the plant.

** Extra genetic material: Genetically engineered foods contain
extra genetic material that is unrelated to the target
characteristics. This extra genetic material can include vectors,
which are added to move genes across natural barriers; promoters,
added to "turn on" the foreign genes; marker genes, added to show
the engineer whether the target gene has been successfully
inserted; and random extra genetic material that the engineer
inserts unintentionally. Here is a brief discussion of each of
these categories:

a) Vectors: Genetic engineering often uses "vectors," genetic
sequences derived from viruses or bacteria, to move genes into
the target cell. One vector used frequently is derived from
AGROBACTERIUM TUMEFACIENS, a bacterium that causes tumors in
plants by inserting DNA from its own genetic code into the
genetic code of the plant. A study published in PROCEEDINGS OF
THE NATIONAL ACADEMY OF SCIENCES in January 2001 reported that
AGROBACTERIUM may be able to insert DNA into human cells as

When AGROBACTERIUM infects a plant under natural conditions, the
genes are incorporated only into the infected part of the plant;
they do not move throughout the plant and are not passed on to
subsequent generations. In contrast, when AGROBACTERIUM genes are
used as vectors in genetic engineering, the resulting plant
includes AGROBACTERIUM genes in all its cells. Conventional
breeding does not require the use of vectors.

b) Promoters: As we have seen, most genetically engineered crops
include the CaMV 35S "promoter" gene to "turn on" the foreign
gene and overcome normal cell defense mechanisms. Viral promoters
are not necessary for conventional breeding.

c) Marker genes: As we saw in REHN #716, genetic engineering
often involves the insertion of antibiotic resistance marker
genes. This does not occur in conventional breeding.

d) Unintentional additions: Sometimes genetic engineers introduce
additional genetic material into the target cell without knowing
it. Last spring, for example, newspapers reported that Monsanto's
Roundup Ready (glyphosate-tolerant) soybeans contained extra
fragments of DNA that the company's genetic engineers were not
aware of having introduced.[8]

On the basis of these points, some people would say that genetic
engineering is "very different" from conventional breeding,
whereas others would say that it is only "somewhat different."
Either way, the differences have obvious implications for the
ways in which governments should regulate genetically engineered
foods. At a minimum, governments should require companies to
conduct pre-market safety tests related to the special hazards
associated with genetic engineering, and any altered foods
allowed onto the market should be labeled.

[To be continued.]


*Rachel Massey is a consultant to Environmental Research

[1] For a thorough collection of resources on agricultural
biotechnology, see AgBioTech InfoNet, maintained by Benbrook
Consulting Services at http://www.biotech-info.net.

[2] Michael K. Hansen, "Genetic Engineering is Not an Extension
of Conventional Plant Breeding; How Genetic Engineering Differs
from Conventional Breeding, Hybridization, Wide Crosses, and
Horizontal Gene Transfer," available at
http://www.consumersunion.org/food/widecpi200.htm. Also see Michael
Hansen and Ellen Hickey, "Genetic Engineering: Imprecise and
Unpredictable," in GLOBAL PESTICIDE CAMPAIGNER, Vol. 10, No. 1,
April 2000, available from Pesticide Action Network
(415-981-1771; panna@panna.org).

[3] Nadia S. Al-Kaff and others, "Plants Rendered
Herbicide-Susceptible by Cauliflower Mosaic Virus-Elicited
Suppression of a 35S Promoter-Regulated Transgene," NATURE
BIOTECHNOLOGY Vol. 18 (September 2000), pgs. 995-999.

[4] Stanley W. B. Ewen and Arpad Pusztai, "Effect of Diets
Containing Genetically Modified Potatoes Expressing GALANTHUS
NIVALIS Lectin on Rat Small Intestine," THE LANCET Vol. 354, No.
9187 (October 16, 1999), pgs. 1353-1354.

[5] Marc A. Lappe and others, "Alterations in Clinically
Important Phytoestrogens in Genetically Modified,
Herbicide-Tolerant Soybeans," JOURNAL OF MEDICINAL FOOD Vol. 1,
No. 4 (July 1999), pgs. 241-245.

[6] Andrew Pollack, "Case Illustrates Risks of Altered Food." NEW
YORK TIMES October 14, 2000. Available at http://www.biotech-

[7] Talya Kunik and others, "Genetic Transformation of HeLa Cells
SCIENCES, published online before print (January 30, 2001). Full
text available for U.S. $5 at

[8] James Meikle, "Soya Gene Find Fuels Doubts on GM Crops," THE
GUARDIAN (London) (May 31, 2000). Available at
Also see "Monsanto GM Seeds Contain 'Rogue' DNA," SCOTLAND ON
SUNDAY (May 30, 2000). Available at http://www.biotech-