Configurational changes in rat liver nuclear chromatin and nucleoli caused by dissociation and reassociation of F1 histone.

Isolated rat liver nuclei treated in 5% perchloric acid (PCA) showed characteristic configurational changes causing a “lace-like” appearance of chromatin. The nucleoli lost their fine granular and fibroreticular structure, resulting in a “coarse granular” configuration. When extracts in 5% PCA were reassociated with the treated nuclei, the chromatin and nucleoli returned to their initial structure. Gel electrophoresis studies revealed that the extracts contained only F 1 histone, that F 1 histone was completely released from the nuclei, and that dissociated F 1 histone reassociated with F 1 histone-depleted nuclei. Chromatin isolated from F 1 histone-depleted nuclei lost the “knob-like” structures, which characterize native chromatin fibers, becoming smooth and fine threads. Chromatin fibers isolated from the reconstituted nuclei recovered their original “knob like” structures. This suggests that F 1 histone plays a crucial role in chromatin and nucleolus structural organization.