Chromatin structure: from nuclei to genes (review).

Characterization of native nuclei by new unharmful biophysical methods, coupled both with the determination of lower order structures in DNA and isolated chromatin, by a variety of sophisticated physicochemical probes and with the intranuclear DNA distribution monitored in situ by high resolution image analysis, recently, point to a unique organization of chromatin-DNA from the secondary up to the quinternary level. Based on the wide range of experimental findings, hereby reviewed in details, a three-dimensional model for DNA structure is proposed from the nuclear level down to the genes, functional units hereby associated with specific structural repeating units. This "fibrosome" model not only accounts for many of the independent observations on the physical and chemical properties of chromatin-DNA, and on the nuclear scaffold and pores, but also accounts for most recent, yet unexplained, discoveries on eukaryotic gene structure, mapping and coding, suggesting a mechanism by which gene expression and cell function may be controlled.