ABSTRACT
The compartmentalization of cellular functions presents a physical barrier between the cytoplasm and the contents of the membrane-enveloped organelles. The enclosure of the genome within a nuclear envelope has necessitated the evolution of nuclear membraneassociated structures termed nuclear pore complexes (NPCs) through which molecules can be transported. Communication between the cytoplasm and nucleoplasm also requires biochemical processes that facilitate and regulate such exchange. NPCs are large proteinaceous assemblies present within pores formed by fusion of the inner and outer nuclear membrane bilayers (INM and ONM, respectively). NPCs are the sites of both active transport (energy and ‘transporter-molecule’ dependent) and passive diffusion of molecules between the cytoplasm and nucleoplasm. Several NPC-specific proteins (nucleoporins) and other NPC-associated proteins also function in a diverse range of cellular processes in addition to their previously characterized roles in the nucleocytoplasmic trafficking. For example, in yeast cells, nucleoplasmic filamentous nucleoporins play a role in the structural and functional organization of chromatin (Galy et al., 2000). Yeast nucleoporins have also been found to be components of the spindle pole body (Chial et al., 1998), while others play a role in cell cycle regulation (Iouk et al., 2002).
