Genes bow out of the limelight
The most detailed probe yet into the workings of the human genome has led scientists to conclude that a cornerstone concept about the chemical code for life is badly flawed.
Analysis of 1% of the human genome has downplayed the role of genes in controlling their own destiny, instead placing so-called junk DNA at centre stage when it comes to gene regulation.
The study, published in more than two dozen papers, takes a small percentage of the genome to pieces to draw up a 'parts list', identifying the biological role of every component.
For the international team of investigators, the four-year project was the computer-equivalent of passing a fine-toothed comb through a mountain of raw data.
Under this view, the genome is rather like a ribbon studded with some 22,000 nuggets in the form of genes, which make proteins, the essential stuff of life.
Genes - deemed so valuable that some discoverers of them have been prompted to file patents over them for commercial gain - amount to only around a 20th, or even less, of the genetic code.
In between the genes and the sequences known to regulate their activity are long, tedious stretches that appear to do nothing.
The term for them is junk DNA, reflecting the presumption that they are merely driftwood from our evolutionary past and have no biological function.
But the work by the ENCODE (ENCyclopaedia of DNA Elements) consortium implies that this nuggets-and-dross concept of DNA should be, well, junked.
The genome turns out to a highly complex, interwoven machine with very few inactive stretches, the researchers report.
Genes, it transpires, are just one of many types of DNA sequences that have a functional role.
And junk DNA turns out to have an essential role in regulating the protein-making business.
Previously written off as silent, it emerges as a singer with its own discreet voice, part of a vast, interacting molecular choir.
"The majority of the genome is copied, or transcribed, into RNA, which is the active molecule in our cells, relaying information from the archival DNA to the cellular machinery," says Dr Tim Hubbard of the Wellcome Trust Sanger Institute, a UK research group that was part of the team.
"This is a remarkable finding, since most prior research suggested only a fraction of the genome was transcribed."
Professor Francis Collins, director of the US National Human Genome Research Institute (NHGRI), which coralled 35 scientific groups from around the world into the ENCODE project, says the scientific community "will need to rethink some long-held views about what genes are and what they do".
"This could have significant implications for efforts to identify the DNA sequences involved in many human diseases," he says.
Another rethink is in the offing about how the genome has evolved, says Collins.
Until now, researchers had thought that the pressure to survive would relentlessly sculpt the human genome, leaving it with a slim, efficient core of genes essential for biological function.
But the ENCODE consortium was surprised to find that the genome appears to be stuffed with functional elements that offer no identifiable benefits in terms of survival or reproduction.
The researchers say there may be a point to this.
Humans could share with other animals a large pool of functional elements, a 'warehouse' stuffed with a variety of tools on which each species can draw, enabling species to adapt according to their environmental niche.