Chromosome conformation by crosslinking: polymer physics matters.

The genetic information is encoded on double-stranded DNA, a long linear polymer chain. Among the central themes of Nucleus will be the advancement of our understanding of how those chains are folded so that they fit into the cell nucleus, and at the same time their information can be read off efficiently. In fact, a quantitative description of the structure of the folded genome is one of the most challenging problems in structural biology, and poses a much more formidable problem than-for instance-the folding of a protein. There are three main reasons for this: first, the genomic DNA is by orders of magnitude the largest biomolecule in the cell; second, it cannot be defined by a single spatial structure because of its flexibility; and third, even if the 'fold' of the genome were more or less defined in any one cell, variations among individual cells may be very large, for the same reasons of flexibility.