'Junk' DNA not junk but key to complexity
Monday, 10 May 2004
What surprised the researchers was that the sequences were highly conserved, that is they remained unchanged for millions of years.
Australian molecular biologists led by Professor John Mattick of the University of Queensland and U.S. researchers from the University of California Santa Cruz report their findings online in the journal Science.
"It's just amazing stuff because nobody ever expected that there would be genetic sequences in our genome which were more highly conserved than protein-coding genes," Mattick said.
The researchers scanned the human, rat and mouse genomes for matching regions of 200 or more DNA base pairs and found 481 regions that were completely unchanged. They then looked at earlier organisms.
"We then looked at the dog and bovine genomes and found that they were preserved there. Amazingly, most of them were preserved in the chicken genome, which has just been released, and about half are preserved in fish," Mattick said.
"So that means some of these sequences have remain unchanged during evolution for over 400 million years."
Mattick said that these sequences remained unchanged while protein-coding genes changed slowly through evolution.
"So whatever [these conserved regions] are, and whatever they're doing, evolution is really saying that they're critical to our biology in ways that we don't yet understand."
Mattick said some of the sequences overlapped with protein-coding genes, while some were outside genes. But all were strongly associated with genes involved in controlling development.
"They're almost certainly regulatory," he said.
New field of genetics?
Mattick said the finding could support the need to focus on a new area of genetics in addition to proteomics, the study of protein gene products.
He likened proteins to a "component set". The key, Mattick said, was finding out what controlled these components. And the more complex the organism, the bigger set of controls would be needed.
"What molecular biology and biochemistry have been doing for the last 50 years now has been studying the components.
"I don't think it really occurred to many people that beyond the components there was another massive level of information required to specify how these components were assembled in complex ways and the control systems to run them."
Mattick likened the evolution of complex organisms to the transition from analog to digital control systems.
"The simple organisms are basically analog devices using proteins both for functions and control systems and that reached a limit," he said. "The complex organisms invented, or evolution did, a digital system which then became a major route to controlling our growth and development.
"Ironically, what was damned as junk might turn out to be the secret of human complexity."