Human mitotic chromosome structure: what happened to the 30-nm fibre?

Abstract

EMBO J 31 7, 1644–1653 February 17 2012

The long-standing view of chromosome packaging is that 10-nm beads-on-a string chromatin fibres fold into higher-order 30-nm fibres, which further twist and coil to form highly condensed chromosomes. After four decades of intense pursuit of the structure and properties of 30-nm chromatin fibres, work of Nishino et al (2012) in this issue of The EMBO Journal demonstrates that regular 30-nm fibres are absent from human mitotic chromosomes. The emerging view is that chromosome-level condensation can be achieved through packaging of 10-nm fibres in a fractal manner.

Figure 1

A new model for explaining how the DNA of mitotic chromosomes is packaged and condensed. In this model, the fundamental unit of chromosome packaging is the 10-nm beads-on-a string chromatin fibre. In all, 10-nm chromatin fibres are not folded into higher-order 30-nm structures. Rather, 10-nm fibres are packaged in a fractal manner such that the structural features of chromosomes are similar at many magnifications. To achieve fractal packaging, the contiguous chromosomal 10-nm fibre must be able to fold back and interact with itself at many levels. Local and at-a-distance contacts between 10-nm fibre segments are mediated by extensive nucleosome–nucleosome interactions.