Human Health Hazards of Common Viral Promoter in GE Foods
On the Human Health Dangers of the Common Viral Promoter (CaMV) Used in
Almost All Genetically Engineered Plants--by Dr. Mae-Wan Ho

Date Posted: 07/15/1999
Posted by:

This is a letter about the cauliflower mosaic virus, whose promoter is
being used in virtually all transgenic plants now on the market and being
field trialed, and arises from an enquiry from The British Society of Plant
Breeders. It makes the vital distinction between the cauliflower mosaic
virus itself, which is not hazardous, and the viral promoter used, which may
13 July 1999

Dr.Penny Maplestone
The British Society of Plant Breeders Limited
Woolpack Chambers, Market Street
ELY, Cambridge CB7 4ND

Dear Dr. Maplestone,

Thank you for your enquiry about the cauliflower mosaic virus (CaMV) and for
the opportunity to clear up a major misconception. I most certainly did not
say, "cauliflower mosaic virus gives you cancer". I was talking
specifically about the cauliflower mosaic viral promoter that is in
virtually all transgenic plants currently on the market or being
field-tested. This is a piece of the virus' genetic material which is being
used to drive the expression of many transgenes. Several factors make this
piece of viral genetic material hazardous.
First, the CaMV promoter is used in a 'naked' form - that is, without its
viral coat. It is now well-known that naked viral DNA is more infectious
than the intact virus, because the viral coat generally determines the host
specificity. For example, DNA from the human polyoma virus can give a full
blown infection when injected into rabbits while the intact virus is
harmless. So the while the intact virus will infect cauliflower and
cabbages, it will almost certainly not gain access to cells of human
beings. The naked viral promoter, however, may well be taken up by mammalian
cells including our own.
Now, foreign DNA taken up into cells are usually degraded, unless they have
a propensity to integrate into the cell's genome. It so happens that the
CaMV promoter is known to have a recombination hotspot, which means it is
especially prone to break and join with other DNA at that point. This
enhances the likelihood of the promoter (and other genes linked with it)
being integrated into the cell's genome.
Integration of foreign DNA into the genome of mammalian cells is well-known
to have harmful effects such as inactivation or activation of host genes
that could lead to cancer.
Another potential hazard of having the cauliflower viral promoter in the
genome is that it could reactivate dormant viruses, which are in the genomes
of all higher organisms including plants and animals, or it could generate
new viruses by recombination. The CaMV is known to be closely related to
human hepatitis B virus and also to retroviruses including HIV and others
that cause cancer.
My research assistant, Angela Ryan and I were among the scientists invited
to Michael Meacher's office to discuss the specific hazards of GM crops at
the end of last March. There, the question of the safety of the CaMV
promoter was specifically raised. The details of that meeting and a briefing
paper I wrote for Michael Meacher afterwards can be found in our Institute
of Science in Society
The latest article on the recombination hotspot of CaMV is Kohli et al
(1999). The Plant Journal 17(6), 591-601. You can find a summary of that
paper on our website.

Yours sincerely,

Dr. Mae-Wan Ho
Institute of Science in Society
and Biology Department, |
Open University.
Walton Hall, Milton Keynes