Chromatin plates in the interphase nucleus.

Early results showed the emanation of chromatin fibers from mitotic chromosomes and nuclei swollen with water. In contrast, under metaphase ionic conditions, it was found that chromatin from mitotic chromosomes is planar and forms multilayered plates. Here, we show that in buffers containing interphase cation concentrations, the chromatin emanated from disrupted nuclei also has a planar morphology. Furthermore, the chromatin fragments produced by micrococcal nuclease digestion of nuclei form the typical beads-on-a-string fibers in the absence of cations, but they self-assemble into plate-like structures in buffers containing magnesium. The plates from interphase nuclei do not form the thick multilayered structures observed in metaphase chromosomes, suggesting that they are more exposed to the medium to facilitate DNA replication and gene expression.