ABSTRACT
The early conception of the cell nucleus was that it was a passive compartment, the main role of which was to keep genetic information separate from the surrounding cytoplasm. The DNA, organized in chromatin fibers, was envisioned as floating like spaghetti in a bowl of fluid nucleoplasm in which the only other structures were ribonucleoprotein particles and the nucleolus. The presence of a more complex substructure was revealed by micro-
scopy and confirmed by the subsequent isolation of the nuclear matrix (NM) [1,2]. The NM is defined as the residual framework structure of the nucleus that maintains many of the overall architectural features of the cell nucleus including the nuclear lamina with complex pore structures, residual nucleoli, and an extensive fibrogranular structure in the nuclear interior. It is operationally defined as a subnuclear structure, which is insoluble following several different extraction procedures (Figure 9.1). It has been identified in a wide range of eukaryotes from yeast to man.
