'Junk' DNA reveals vital role
Inscrutable genetic sequences seem indispensable.
7 May 2004
HELEN PEARSON

If you thought we had explored all the important parts of our genome, think
again. Scientists are puzzling over a collection of mystery DNA segments
that seem to be essential to the survival of virtually all vertebrates. But
their function is completely unknown.

The segments, dubbed 'ultraconserved elements', lie in the large parts of
the genome that do not code for any protein. Their presence adds to growing
evidence that the importance of these areas, often dismissed as junk DNA,
could be much more fundamental than anyone suspected.

David Haussler of the University of California, Santa Cruz, and his team
scanned the genome sequences of man, mouse and rat1. They found more than
480 ultraconserved regions that are completely identical across the three
species. That is a surprising similarity: gene sequences in mouse and man
for example are on average only 85% similar. "It absolutely knocked me off
my chair," says Haussler.

The regions largely match up with chicken, dog and fish sequences too, but
are absent from sea squirt and fruitflies. The fact that the sections have
changed so little in the 400 million years of evolution since fish and
humans shared a common ancestor implies that they are essential to the
descendants of these organisms. But researchers are scratching their heads
over what the sequences actually do.

The most likely scenario is that they control the activity of indispensable
genes. Nearly a quarter of the sequences overlap with genes and may be
converted into RNA, the intermediate molecule that codes for protein. The
sequences may help slice and splice RNA into different forms, Haussler
suggests.

Another set may control embryo growth, which follows a remarkably similar
course in animals ranging from fish to humans. One previously identified
ultraconserved element, for example, is known to direct a gene involved in
the growth of the brain and limbs.

To solve the conundrum, experts predict a flurry of studies into the
enigmatic DNA chunks. "People will be intrigued by this [finding]," says
Kelly Frazer who studies genomics at Perlegen Sciences in Mountain View,
California. "It is the kind of stuff that blows people away."

Read the rest at Nature:
http://www.nature.com/nsu/040503/040503-9.html

Comment:
If the "junk DNA", intron, is not junk afteral, then we haven't sequences
the the human genome at all - we have only catelogued the 'classic' protien
coding DNA, and not the all important (?) ultraconserved elements..

Posted by
Robert Karl Stonjek.
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