[extropy-chat] junk *is* junk

[Damien Broderick]

..apparently:

================

By SYLVIA PAGAN WESTPHAL
New Scientist

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.

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."