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4.3 Product-specific detection methods and available sequence information
Product-specific detection methods based on PCR technology ideally
employ target sequences uniquely found in the respective genetically
engineered organism. This can be accomplished by choosing primers
that bind to two different adjacent genetic elements combined
in the respective product but which are found neither naturally
in that combination nor in any other known approved transgenic
product. These primers result in amplification products containing
interfaces between unique1
- regulatory sequences and structural genes,
- leader sequences (e.g. chloroplast transit peptide sequences)
and structural genes,
- different regulatory elements, or
- the interface between the genomic sequence of the host plant
and the DNA that was introduced.
Specifically altered sequences of structural genes to allow
plant-specific codon usage (here, termed 'synthetic' genes) or
chimeric constructs may also allow specific identification of
the respective products.
The availability of precise and comprehensive sequence information
is an important prerequisite for the development of such product-specific
DNA-based detection methods. If products have been approved that
may have originated from various transformation events, the data
should also assess differences in the content of genetic elements
between these lines. Ideally, the data should include complete
sequences of the vectors used for plant transformation, knowledge
as to which parts of the plasmid are stably integrated into the
host genome as well as the sequences of the sites of integration,
when possible. Minimal requirements are specific sequence information
on a unique expression cassette (promoter-structural gene-terminator)
or the sequence of a transgene with altered codon usage.
Some of the sequence information that has been disclosed on the
currently approved genetically modified agricultural crops is
presented in Released sequence information on genetic elements introduced into genetically engineered crops.
1 In order to distinguish different
genetically modified products containing, for example, the same (trans-)
gene and promoter, but divergent untranslated sequences in between, the
length of the amplicon may also be considered as a factor to achieve a