Life goes on without 'vital' DNA
Sylvia Pagán Westphal, Boston
16:30 03 June 04

It is not often that the audience at a scientific meeting gasps in amazement
during a talk. But that is what happened recently when researchers revealed
that they had deleted huge chunks of the genome of mice without it making
any discernable difference to the animals.

The result is totally unexpected because the deleted sequences included
so-called "conserved regions" thought to have important functions.

All DNA tends to acquire random mutations, but if these occur in a region
that has an important function, individuals will not survive. Key sequences
should thus remain virtually unchanged, even between species. So by
comparing the genomes of different species and looking for regions that are
conserved, geneticists hope to pick out those that have an important
function.

It was assumed that most conserved sequences would consist of genes coding
for proteins. But an unexpected finding when the human and mouse genomes
were compared was that there are actually more conserved sequences within
the deserts of junk DNA, which does not code for proteins.

The thinking has been that these conserved, non-coding sequences must, like
genes, be there for a reason. And indeed, one group has shown that some
conserved regions seem to affect the expression of nearby genes.

Virtually indistinguishable

To find out the function of some of these highly conserved
non-protein-coding regions in mammals, Edward Rubin's team at the Lawrence
Berkeley National Laboratory in California deleted two huge regions of junk
DNA from mice containing nearly 1000 highly conserved sequences shared
between human and mice.

One of the chunks was 1.6 million DNA bases long, the other one was over
800,000 bases long. The researchers expected the mice to exhibit various
problems as a result of the deletions.

Yet the mice were virtually indistinguishable from normal mice in every
characteristic they measured, including growth, metabolic functions,
lifespan and overall development. "We were quite amazed," says Rubin, who
presented the findings at a recent meeting of the Cold Spring Harbor
Laboratory in New York.

He thinks it is pretty clear that these sequences have no major role in
growth and development. "There has been a circular argument that if it's
conserved it has activity."

Read the rest at New Scientist
http://www.newscientist.com/news/news.jsp?id=ns99995063

Posted by
Robert Karl Stonjek.
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