Despite the enormous current interest in gene expression and its
role in biology, very little is known about the structural and
functional environment within which gene expression occurs. The
molecular composition and spatial organization of even the most
rudimentary extra-chromosomal nuclear components remain unclear.
Indeed, the existence of any internal nuclear structural
features other than the nucleolus or chromatin (e.g. the so-
called nuclear skeleton or matrix) remains controversial (for
reviews, see Cook, 1988; Fisher, 1989; Jackson, 1991). In this
uncertain situation, the few universally accepted com- ponents
of the nucleus (e.g. the nuclear envelope and the nucleolus)
have become strong foci of study, in part because they may
represent examples of more global nuclear organiz- ing
principles. The best characterized of these components is the
fibrous, proteinaceous network on the inner (nucleoplas- mic)
face of the nuclear envelope, the nuclear lamina. The major
proteins of the nuclear lamina, designa