Figure 3

A simplified representation of a model for nuclear dynamics. (a) Chromatin loci and nuclear bodies are constrained within a nuclear subvolume, either by tethering to another structure or by physical boundaries to their movements. (b) Movement of a locus or nuclear body to a new location entails, first, relaxation of tethering or removal of the physical barrier. This is followed by transit to one or more new sites in the nucleus, and transit ends as a result of either binding via specific factors at a new location or encountering a new physical constraint. The new site can place the locus in either an active (c) or a repressive (heterochromatin) (d) domain. Current evidence suggests that movement between compartments is likely to be the result of passive diffusion, although at present we cannot exclude the possibility that energy-mediated movements might also occur.