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Contact: Internet: hokef@mail.med.upenn.edu |
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June 1997 Mobile Elements in
Non-Coding DNA May Be Relatively Common About 95 percent of the human genome is estimated to be
non-coding, meaning that it appears to play no direct role
in producing the proteins that constitute the body and
conduct its life processes. Among these vast stretches of
genetic material -- once erroneously referred to as junk DNA
-- are about 100,000 sequences known as long interspersed
nuclear elements, or L1 elements. Most of these L1 sequences
are thought to be inert, but two have been shown previously
by researchers at the University of Pennsylvania Medical
Center to be active and mobile, capable of jumping from one
location in the genome to another where they then randomly
reinsert themselves. This series of events is called
retrotransposition, and when the insertion point disrupts a
DNA sequence that codes for a needed gene, the result can be
disease. Now, using several innovative assay techniques, including
one to hunt for retrotransposition occurrences in cultured
cells, the Penn group has raised the number of known active
L1 elements to seven. Based on the new findings, published
in the May issue of Nature Genetics, they estimate
that as many as 30 to 60 active L1 elements may reside in
the total human genome. The purpose for these mobile DNA
elements, proven able to interfere with the function of
genes at times, is unclear to scientists. But there are
tantalizing clues suggesting that they must play an
important role of some kind. One such clue is their
prevalence and another is their apparent longevity. "There are sequences in these elements that are similar
to sequences in certain bacteria, so from an evolutionary
point of view they are very old," notes
Haig H. Kazazian, Jr., MD, chairman of the
department of genetics and senior author on the study. "And
they have expanded in the last 50 million years or so,
especially in mammals. We suspect they may be a key force
for diversification during evolution -- a mechanism,
perhaps, for increasing the plasticity of the genome." The University of Pennsylvania Medical Center's sponsored research ranks fifth in the United States, based on grant support from the National Institutes of Health, the primary funder of biomedical research in the nation -- $149 million in federal fiscal year 1996. In addition, for the second consecutive year, the institution posted the highest growth rate in its research activity -- 9.1 percent -- of the top 10 U.S. academic medical centers during the same period. News releases from the University of Pennsylvania Medical Center are available to reporters by direct e-mail, fax, or U.S. mail, upon request. They are also posted electronically to the medical center's home page (http://www.uphs.upenn.edu) and to EurekAlert! (http://www.eurekalert.org), an Internet resource sponsored by the American Association for the Advancement of Science. |
