[Ultrastructure of the DNP fibrils and of the interchromatin granules in isolated nuclei of the rat liver].

The structural organization of DNP fibrils and interchromatin granules of isolated rat hepatocyte nuclei has been studied in various conditions of chromatin solubilization. When observed either in nuclei fixed in situ or in a solution containing 20 mM TEA and 1 mM MgCl2, a DNP fibril consists of globular structures 20--25 nm in diameter. In the nuclei fixed in a magnesium-free solution (20 mM TA), nucleosome structures are revealed in DNP. Condensation of chromatin results from interaction between 20 nm globular fibrils, whereas the complete dispersion of chromatin is a consequence of its conversion into the nucleosomal form. In the conditions of both DNP structuralization and dispersion, the nuclei are revealed to contain zones of interchromatin granules connected by thin fibrils. It is assumed that the different compactness of these granular-fibrillar complexes and of the regions of condensed chromatin may be used for their separation and fractionation.