NUCLEAR ASSEMBLY

We review old and new insights into the structure of the nuclear envel ope and the components responsible for its dynamic reassembly during m itosis. New information is coming to light about several of the protei ns that mediate nuclear reassembly. These proteins include the lamins and their emerging relationship with proteins such as otefin and the M AN antigens: peripheral proteins that might participate in lamina stru cture. There are four identified proteins localized to the inner nucle ar membrane: the lamina-associated proteins LAP1 and LAP2, emerin, and the lamin B receptor (LBR). LBR can interact independently with lamin B and a chromodomain protein, Hp1, and appears to be a central player in targeting nuclear membranes to chromatin. Intermediates in the ass embly of nuclear pore complexes (NPCs) can now be studied biochemicall y and visualized by high resolution scanning electron microscopy. We d iscuss the possibility that the filament-forming proteins Tpr/p270, Nu MA, and perhaps actin may have roles in nuclear assembly.