Unfurled, the human genome would contain approximately six feet of DNA. Amazingly, all of that length is packed into a cell nucleus about three micrometers in diameter--roughly one-tenth the width of a human hair.
|Fractal genome: Researchers theorize that DNA molecules inside
the cell nucleus are packed into a compact, unknotted structure called
a fractal globule (shown above), making it easy to pack and unpack.
Adjacent regions in the linear chain of DNA are indicated using similar
Credit: Leonid A. Mirny and Maxim Imakaev
New technology that makes it possible to assess the three-dimensional interactions among different parts of the genome has revealed how these molecules are packed into such a tiny space. The findings could also yield new clues to genome regulation--how specific genes are turned on and off.
While scientists have previously been able to resolve the three-dimensional structure of parts of the genome, a new study is the first to do so on a genome-wide scale. "Our technology is kind of like MRI for genomes," says Erez Lieberman-Aiden, a researcher in the Harvard-MIT Division of Health Sciences and Technology and one of the authors of a new paper detailing the work. (Lieberman was named to Technology Review's TR35 list young innovators this year).
DNA has multiple levels of organization--the linear sequence of bases, its famous helical structure, and higher-order formations that wrap it around proteins and coil it to form chromosomes. But identifying how DNA is organized at these higher levels across the genome has been difficult. "We have the entire linear sequence of the genome, but no one knows even the principles of how DNA is organized in higher-order space," says Tom Misteli, a scientist at the National Cancer Institute, in Bethesda, MD, who was not involved in the study.