The researchers report 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.
For decades, some cell biologists suspected that the genome’s compression wasn’t just an efficient storage mechanism, but linked to the very function and interaction of its genes. But this wasn’t easy to study: Sequencing the genome destroys its shape, and electron microscopes can barely penetrate its active surface. Though its constituent parts are known, the genome’s true shape has been a mystery.