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Fractal Architecture Permits Incredibly Tight Packing of Cellular DNA

Using a new technique called Hi-C, scientists have deciphered the three-dimensional structure of the human genome, paving the way for new insights into genomic function. The researchers reported two striking findings. First, the human genome is organized into two separate compartments, keeping active genes separate and accessible while sequestering unused DNA in a denser storage compartment. Chromosomes snake in and out of the two compartments repeatedly as their DNA alternates between active, gene-rich and inactive, gene-poor stretches. Second, at a finer scale, the genome adopts an unusual organization known in mathematics as a "fractal." The specific architecture the scientists found, called a "fractal globule," enables the cell to pack DNA incredibly tightly--the information density in the nucleus is trillions of times higher than on a computer chip--while avoiding the knots and tangles that might interfere with the cell's ability to read its own genome. Moreover, the DNA can easily unfold and refold during gene activation, gene repression, and cell replication. The fractal globule architecture, while proposed as a theoretical possibility more than 20 years ago, has never previously been observed. "Nature's devised a stunningly elegant solution to storing information--a super-dense, knot-free structure," said senior author Dr. Eric Lander, director of the Broad Institute. This paper is featured on the cover of the October 9 issue of Science. [Press release]