Scaffolding Ubiquitous Fibre Forming Components and Their Associated Functions

The backbone of eukaryotic nuclei can be isolated and characterized according to protocols that have been optimized for the removal of soluble proteins, such as his-tones. For instance, the scaffolds resisting LIS extraction contain components from three nuclear compartments, (1) the lamina (lamins A-C), (2) the nucleolus (nucleolin) and (3) the fibrogranular internal network intermediate filament (IF-type proteins). Luderus et al. (1992, 1994) have studied the distribution of S/MAR binding centres over the scaffold and found attachment sites distributed equally over the peripheral nuclear lamina and the internal fibrogranular network. The domains observed in nuclear matrix preparations by confocal or electron microscopy are neither collapsed nor floating free. They are rather retained in a precise spatial relationship to other landmarks, demonstrating the function of such a supporting structure. The core of these non-chromatin nuclear structures is formed by the fibrogranular ribonucleoprotein (RNP) network together with two networks of intermediate filaments that stabilize the nuclear envelope from both the outside and the inside. On the outside, a cocoon of filaments connects the nucleus with the cytoskeleton, while the inner face of the nuclear membrane and the nucleus' interior is reinforced by lamins. In combination with these networks, S/MARs impart a wide spectrum of functional properties as they restrict genomic areas to particular nuclear compartments.

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