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 developmen
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Contact: Claire Bowles
claire.bowles@rbi.co.uk
44-207-331-2751
New Scientist
2-Jun-2004