THE NUCLEAR MATRIX REVEALED BY ELUTING CHROMATIN FROM A CROSS-LINKED NUCLEUS

The nucleus is an intricately structured integration of many functiona l domains whose complex spatial organization is maintained by a nonchr omatin scaffolding, tile nuclear matrix, We report here a method for p reparing the nuclear matrix with improved preservation of ultrastructu re. After the removal of soluble proteins, the structures of the nucle us were extensively cross-linked with formaldehylde. Surprisingly, the chromatin could be efficiently removed by DNase I digestion leaving a well preserved nuclear matrix. The nuclear matrix uncovered by this p rocedure consisted of highly structured fibers, connected to the nucle ar lamina and built on an underlying network of branched IO-nm core fi laments, The relative ease with which chromatin and the nuclear matrix could be separated despite extensive prior cross-linking suggests tha t there are few attachment points between the two structures other tha n the connections at the bases of chromatin loops, This is an importan t clue for understanding chromatin organization in the nucleus.