The nuclear membranes, nuclear pore complexes and the nuclear lamina are the major structural components of the nuclear envelope (Worman and Courvalin, 2000). The nuclear membranes can be divided into three morphologically distinguishable continuous domains (Figure 1). The outer nuclear membrane is a direct continuation of the rough endoplasmic reticulum, sharing proteins with it and also containing ribosomes on its outer surface. The inner nuclear membrane is closest to the nucleoplasm and is associated with the nuclear lamina. The pore membranes connect the inner and outer nuclear membranes at numerous locations and are associated with the nuclear pore complexes.