SSS 2009-10-09（在线收听）

If the human genome were put in a straight line, it would be over six and a half feet long. So how do you store all that DNA in a tiny nucleus? And have the cell manage it? Researchers explain how in a study featured on the cover of the October 9th issue of the journal Science.

Using new analytic techniques, Erez Lieberman and colleagues found that the genome is packed into what’s called a “fractal globule”—despite being intensely twisted, the string of genes never knots. This type of shape was mathematically postulated over a century ago, and has now been shown to describe the genome’s three-dimensional structure.

But the big finding is that the cell nucleus has two compartments—and genes are only active in one. All cells carry the same complete genome, but different genes get turned on, for example, in a liver cell compared with a nerve cell. Turns out that the genes to be used in a given cell get shuttled into the nucleus’s active section. Dormant genes stay out. The system allows each cell to make sense of information stored trillions of times more densely than what’s on a computer chip.