June 14, 2007 — 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.
The ground-breaking study, published in more than two dozen papers in journals on both sides of the Atlantic, 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.
Reporting in the British journal Nature and the U.S. journal Genome Research on Thursday, they suggest that an established theory about the genome should be consigned to history.
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 twentieth, 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," said Tim Hubbard of the Wellcome Trust Sanger Institute, a British 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."
