ABSTRACT
Architecturally, the nuclear envelope is a double membrane system comprised of inner and outer leaflets. The outer leaflet is studded with ribosomes and is found to be continuous with the rough-surfaced endoplasmic reticulum, whereas the inner leaflet is devoid of polysomes and is usually found in close association with chromatin. Both the inner and outer membranes are joined wherever pore complexes are formed, and electron microscopic examination of these junctions in ultrathin sections reveals that the inner and outer membranes are continuous in these regions. Studies designed to examine the molecular associations of the lamins in intact rat liver nuclear envelope indicate that a significant percentage of lamm B is cross-linked in the native membrane by disulfide bridges to form two electrophoretically distinct polymeric species, both of which appear to be trimers. Immunochemical data clearly show the association of one or more of the lamins with the fibrous lamina.
