Jan.
3, 2013 — Much of the DNA that makes up our genomes can be traced back to
strange rogue sequences known as transposable elements, or jumping genes, which
are largely idle in mammals. But Johns Hopkins researchers report they have
identified a new DNA sequence moving around in bats -- the first member of its
class found to be active in mammals. The discovery, described in a report
published in December on the website of the Proceedings of the National Academy
of Sciences, offers a new means of studying evolution, and may help in
developing tools for gene therapy, the research team says.
"Transposable
elements are virtually everywhere in nature, from bacteria to humans,"
says Nancy Craig, Ph.D., a Howard Hughes investigator and professor in the
Johns Hopkins University School of Medicine's Department of Molecular Biology
and Genetics. "They're often seen as parasites, replicating themselves and
passing from generation to generation without doing anything for their hosts.
But in fact they play an important role in fueling adaptation and evolution by
adding variability to the genome."
As
their name suggests, jumping genes can move from place to place in the genome,
sometimes even inserting themselves into the middle of another gene. Some work
by replicating themselves and inserting the copies into new places in the
genome -- retroviruses such as HIV are composed of this type of jumping gene,
which enables the host cell to be hijacked to make more virus particles.
Another class of jumping genes, known as "DNA cut-and-paste," doesn't
make copies, but instead cuts itself out of one site in the genome before
hopping into another. Craig explains that in mammal genomes, most jumping genes
are of the copy-and-paste variety, and most of these are fossils, mutated to
the point where they can no longer move about. Although some remnants of
cut-and-paste jumping genes have been unearthed in mammals, until now, all of
them have been inactive.
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