May 10, 2004

» 'Junk DNA' sequences turn out to be identical in men, dogs, chickens, mice and fish. It must be doing something

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 rat. 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.