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Thursday, February 22, 1996, 12:00 p.m. EDT
In a step that could speed gene research and that could help in the development of gene therapies, scientists at the National Institute of Environmental Health Sciences have found a way to isolate and clone genes and other chromosome fragments directly.
The method bypasses the lengthy, indirect and cumbersome methods in current use.
The approach was developed in the NIEHS laboratory of Michael Resnick, Ph.D., in collaboration with two visiting Russian scientists, Vladimer Larionov, Ph.D., and Natasha Kouprina, Ph.D., who are on leave from the Institute of Cytology in St. Petersburg.
Francis S. Collins, M.D., Ph.D., Director of the National Center for Human Genome Research, which helped fund the research, said, "This method will help us to focus on specific regions of human chromosomes in order to better understand origins of disease and to develop diagnosis of genetic diseases."
The new method relies on cloning DNA, the chemical of inheritance, into yeast cells. These cells are the same material bakers use to make bread rise. Dr. Resnick said, "We can now rapidly isolate specific fragments of human genetic material. Using this new method, the isolated genes and DNA fragments can subsequently be manipulated and engineered."
The old way of isolating specific DNA fragments or genes involved randomly cutting the DNA from cells into many thousands or millions of pieces. The pieces were then treated so that they could be cloned into yeast or bacteria. Each cloned piece had to be examined to find the wanted fragment or gene.
The new approach exploits the natural ability of yeast cells to find and combine similar DNAs whether the DNA is from humans, animals or plants. This recombination process has been a central topic in Dr. Resnick's laboratory for many years.
Human DNAs are introduced (transformed) into yeast cells along with a very small piece of the gene or fragment that is wanted. Only DNA that matches the small piece are maintained, or cloned, as yeast cells reproduce.
The investigators have used this approach to isolate DNA regions from chromosomes 10, 16, and 22, regions that include several known disease genes. The cloning method is called TAR, which stands for transformation-associated recombination.
"In thinking about this cloning method," Dr. Resnick said, "we liken the genetic material to a bag of different colored marbles and each marble has a small amount of information. Previously each marble had to be isolated in a separate box and then the color could be determined. Now, all the marbles of a desired color can be isolated in a box and the rest can be thrown away."
"TAR cloning provides a potentially powerful new method for selectively cloning specific genes or other chromosome segments from the total genome," said David A. Smith, Manager of the Department of Energy's Human Genome Program, which provided partial support initially for Drs. Larionov and Kouprina efforts at NIEHS.
Dr. Resnick added, "This approach is expected to provide opportunities to better understand errors in genetic diseases as well as to aid in the isolation of chromosomal material to be used in gene therapy."
His Russian coauthors in reporting the advance in the Proceedings of the National Academy of Sciences joined Dr. Resnick at NIEHS as visiting scientists in the midst of major changes in the then Soviet Union. "Our highly productive merger and the development of this new method came about during a period of uncertainty in the funding of science in their home country. I am pleased that we had the opportunity to help them continue their research and bring together our common interests," Dr. Resnick said.
The three scientists are now collaborating with others at NIEHS, including Scientific Director J. Carl Barrett, Ph.D. to apply the method to research in genetic diseases. Dr. Barrett's laboratory has had key roles in the identification of breast cancer and prostate cancer suppressor genes. They also initiated collaborations with several labs in the U.S. and abroad on issues of human chromosome structure and disease.
Dr. Kenneth Olden, NIEHS Director, said, "The development of this approach has occurred because the right people were in the right place at the right time. The Institute was able to provide a helping hand. I look forward to the application of this method to many areas of research and to the contribution this will make to public health."
NIEHS, one of the National Institutes of Health, is located in Research Triangle Park, N.C., and is interested in the effects that natural and man-made factors in the environment have on human genes and human health and the reverse -- the varying susceptibility of humans to environmental insults.
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