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, designated nuclear lamins
(Gerace and Blobel, 1980), have undergone extensive
molecular characterization in the last decade. Lamins are now