To create that genetically modified corn everybody's freaking out about, scientists have to chopping out a sequence of base pairs. These chemical scissors do the snipping.

When a cell suffers damage to its DNA known as a double-strand break, the cell use two accurate repair processes to fix the damage: Homologous recombination, which uses the code from an undamaged sister-chromatid as a template, and non-homologous end joining, which essentially reconnects the two broken ends.

Zinc finger nuclease technology—essentially chemical scissors used to cut DNA—exploits this process to either knock out a specific section of the DNA strand that turns off the gene expression or remove and replace it with a donor strand that modifies the gene's function.

To do this, researchers employ artificial restriction enzymes called zinc finger nucleases. Restriction enzymes literally cut single strands of DNA at a specific nucleotide sequence known as a restriction site. A single ZFN is comprised of two functional parts, or domains. The cleavage domain uses an enzyme found in Flavobacterium okeanokoites, rod-shaped bacteria the live in soil and fresh water, to cut the outer bond of the DNA strand that each nucleotide base sits on. The other are Zinc finger proteins—short, modular proteins that can be combined to target and match with specific sequences on the DNA strand.

Previous gene therapy techniques were severely limited by their low efficiency. ZFN technology greatly improves the efficiency since double-cutting the DNA strand stimulates the natural DNA-repair processes and forces the DNA's recombination.

So, this is all delightfully technical and all but what does it do? Simply put, gene therapy. In plants and animals. The Monsato company, for example, is set to begin selling genetically modified corn on the US markets that produces its own Bt toxins (an insecticide). In addition, ZFN technology is helping advance the science of transplantation. As Richard Insel, M.D., Chief Scientific Officer for the Juvenile Diabetes Research Foundation, explained to Medical-News, it may help create pig tissue that is less immunogenic and more easily transplantable into humans,

This work is a major advance because it provides an efficient method of knocking out any desired gene in the pig. ZFN-mediated genome editing can be used to make porcine cells and tissues less immunogenic and more suitable for transplantation into humans. In the example of type 1 diabetes, pancreatic islets can be replaced by transplanting functioning ones into a patient. However, we face a severe shortage of human cadaver organs in the U.S. and cannot satisfy the transplantation needs of people with the disease. Using ZFN-modified pigs as a source of tissues for human transplantation may prove to be a promising solution to the shortage of donated human organs for diabetes and other diseases.

[Oxford Journal - Signma Aldrich - Restriction Enzyme Wiki - Zinc Finger Nuclease Wiki - News-Medical.net - Nature]

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