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June 12, 2000


Mae-wan Ho


AgBioView - http://www.agbioworld.org, http://agbioview.listbot.com

At 12:09 PM 10/6/00 -0500, you wrote:
MW Ho Wrote:

> Due to their
> highly mixed origins, however, GM-constructs are more
> unstable than natural genetic material as well as more
> invasive; and may therefore be more likely to spread to
> unrelated species.
> Those points were not challenged by Prakash because these
> basic principles and observations of genetic engineering are
> covered in text books and are also areas of active research.

I have come across Ho's claims before about chimeric molecules being unstable
and her claim that this is the subject of text books. The text book she refers
to is infact Principles of Genetic Manipulation: RW
Old and SB Primrose 5th edition (1994), chapter 8, page 164 - Structural
Instability. I have actually taken the time to look at this text - something
that, incidently, Angela Ryan, MW Ho's side kick has not actually done last
time I coresponed with her.

This text book actually refers to data about non-chimeric molecules being
unstable because of repetative sequences and has zero relevance to Ho's
that chimeric molecules are inherantly unstable

What Old and Primrose does say is: "A common feature of these deletions is
the involvement of homologous recombination between short direct repeats".

Ie DNA is unstable if they have repeat regions. Molecules like this are
subject to recombination whether they are naturally occurring (such as in
the "junk DNA" of eukaryotes - witness the variation in the length of tandem
repeats of repetative DNA used as markers for gene mapping in eukaryotes) or
whether they are chimeric molecules. It is
dependant on the repetition of DNA sequences not on the chimeric nature of
the molecule.

Old and Primrose also talk about other situations where plasmid molecules
are subject to deletions. It references Michel and Ehrlich 1986 which
reports deletions in NON-CHIMERIC E.coli chromosomes. It also refers to
instability due to the NATURALLY occurring transposable elements - nothing
to do with chimeric molecules.

Another situation where deletions form is when attempts are made to
express proteins at high levels in E.coli from chimeric plasmids. If the
protein is toxic to the cell then there is high selection pressure to form
mutants of the plasmid which have deletions of the chimeric plasmid. This
occurs only in specific situations depending on the nature of the protein
that is being expressed. It is possible because of the nature of bacterial
cultures there are large numbers of cells to select from and thus rare
mutants can quickly dominate a culture. It is due to the toxic nature of the
gene product not to the "chimeric nature" of the DNA molecule. This has zero
relevance to the situation in transgenic plants. Chimeric molecules producing
non-toxic proteins are completely stable (Witness the ability of scientists to
exchange plasmids with each other. Witness the ablity of different sequencing
labs to sequence shared clones and get 100% matches)

MW Ho's ability to back up her claims is limited so far to misquoting from a
text book.

Dr Roger Morton 02 6246 5069 (ph)
CSIRO Plant Industry 02 6246 5000 (fax)
GPO Box 1600 roger.morton@pi.csiro.au