Last September, Scientific American published an article, “Hidden Treasures in Junk DNA,” which explained how much of our DNA came to be wrongfully known as junk:
In the 1970s, when biologists first glimpsed the landscape of human genes, they saw that the small pieces of DNA that coded for proteins (known as exons) seemed to float like bits of wood in a sea of genetic gibberish. What on earth were those billions of other letters of DNA there for? No less a molecular luminary than Francis Crick, co-discoverer of DNA’s double-helical structure, suspected it was “little better than junk.”
The phrase “junk DNA” has haunted human genetics ever since. In 2000, when scientists of the Human Genome Project presented the first rough draft of the sequence of bases—or code letters—in human DNA, the initial results appeared to confirm that the vast majority of the sequence—perhaps 97 percent of its 3.2 billion bases—had no apparent function.
But new findings, some of which were outlined in that Scientific American article, have demonstrated that “junk DNA” is a term that should be tossed in the garbage. Some of it turns out to be rather important.
According to UNC pharmacologist Zefeng Wang and his colleagues, about 10 percent of each gene is responsible for producing the proteins that make the cells do what they’re supposed to do. Those producer regions are called exons.
But there’s another process that contributes to how genes function and why diseases occur: gene assemblage, or how genes are spliced together. That process, which Wang and colleagues describe in the January 2013 issue of Nature Structural & Molecular Biology, can involve exons or introns—the long stretches of genetic material that make up about 90 percent of a single gene.
Introns have been referred to as the dark matter of genetic code—or junk DNA—because introns are cut out and destroyed during the process by which genes express their functions. So scientists haven’t been able to deduce what introns do, until now.
Wang’s team has found that bits of the intronic region can recruit protein factors that play roles in the splicing process.
“It turns out that the sequencing element in both exons and introns can regulate the splicing process,” Wang says. “We call it the splicing code, which is the information that tells the cell to splice one way or the other. And now we can look at these variant DNA sequences in the intron to see if they really affect splicing, or change the coding pattern of the exon and, as a result, protein function.”
Read more at Futurity.org, a website dedicated to research from top universities in the United States, Canada, Great Britain, and Australia.
Zefeng Wang is an assistant professor of pharmacology in the School of Medicine and a member of the Lineberger Comprehensive Cancer Center. His collaborators include Yang Wang, a research assistant professor in Zefang Wang’s lab.
Date: Feb 1, 2013