Abstract
The structure of compact 30-nm chromatin fibres is still debated. We present here a novel unified model that reconciles all experimental observations into a single framework. We propose that compact fibres are formed by the interdigitation of the two nucleosome stacks in a 2-start crossed-linker structure to form a single stack. This process requires that the dyad orientation of successive nucleosomes relative to the helical axis alternates. The model predicts that, as observed experimentally, the fibre-packing density should increase in a stepwise manner with increasing linker length. This model structure can also incorporate linker DNA of varying lengths.