The nuclear envelope is a complex structure with multiple functions. It is composed of outer and inner lipid bilayer membranes, nuclear pores and nuclear lamina. The two nuclear membranes are separated by a 20-40 nm perinuclear space and are connected at the nuclear pore complexes (NPCs). The NPCs are passageways for transport of macromolecules between the nucleoplasm and the cytoplasm. The NPC is a large protein complex composed of 100 different proteins, termed nucleoporins, with an estimated molecular weight of 120 MDa. The membrane domain of the NPC has a unique content of both integral and peripheral proteins. In mammalian species the only known integral proteins of this membrane domain are
gp210 and POM121. A
gp210 cDNA clone was previously isolated from rat, and anti-
gp210 antibodies were previously obtained in rat and Drosophila, and were used to map the transmembrane domain and to show that the large amino part of
gp210 is embedded in the perinuclear space. The
gp210 protein was found to be involved in nuclear transport since anti-
gp210 antibodies can interfere with transport through the nuclear pores. Previous studies, using cell free systems from Drosophila and Xenopus also suggested a role for
gp210 in nuclear pore assembly. Computer search in Drosophila databases revealed EST clones with significant homology to the rat
gp210. These clones were used to obtain the complete sequence of the Drosophila
gp210 and to detect a homologue in Caenorhabditis elegans. The C. elegans
gp210 protein is 25% and 34% identical and 44% and 55% similar to the rat and the Drosophila
gp210 proteins, respectively. More strikingly is the conservation of the general structure of the protein and the location of the transmembrane domain in all
gp210 homologues. This evolutionary conservation of the protein indicates a functional conservation of
gp210 in nuclear pore assembly and activity. In order to gain more information about the role of
gp210 in both nuclear pore assembly and nuclear transport, we have started double stranded RNA mediated interference experiments and we are currently screening for deletions in the
gp210 gene. In addition, we have produced a fusion protein of
gp210 and are currently making antibodies against the protein.