Aspects of nucleosomal positional flexibility and fluidity

Nucleosomes have been considered until recently to be stable and uniquely
localized particles. We focus here on two properties of nucleosomes that
are emerging as central attributes of their functions: mobility and
multiplicity of localization. The biological relevance of these phenomena
is based on the fact that chromatin functions depend on the relative
stability of nucleosomes, on their covalent or conformational
modifications, their dynamics, their localization, and the density of
their distribution. In order to understand these complex behaviors both
the structure of the nucleosome core particles and the informational rules
governing their interaction with defined DNA sequences are here taken into
consideration. The fact that nucleosomes solve the problem of how to
locate a specific interaction site on a potentially infinite combination
of sequences, with interactions recurring to a controlled level of
informational ambiguity and stochasticity, is discussed. Nucleosomes have
been shown to slide along DNA. This novel facet of their behavior and its
implications in chromatin remodeling are reviewed.