NUP84, A NOVEL NUCLEOPORIN THAT IS ASSOCIATED WITH CAN NUP214 ON THE CYTOPLASMIC FACE OF THE NUCLEAR-PORE COMPLEX/

The short filaments extending from the cytoplasmic face of nuclear por e complexes are thought to contain docking sites for nuclear import su bstrates. One component of these filaments is the large O-linked glyco protein CAN/Nup214. Immunoprecipitation studies carried out under nond enaturing conditions, and using a variety of antibodies, reveal a nove l nonglycosylated nucleoporin, Nup84, that is tightly associated with CAN/Nup214. Consistent with such an association, Nup84 is found to be exposed on the cytoplasmic face of the nuclear pore complex. cDNA sequ ence analyses indicate that Nup84 contains neither the GLFG nor the XF XFG repeats that are a characteristic of a number of other nuclear por e complex proteins. Secondary structure predictions, however, suggest that Nup84 contains a coiled-coil COOH-terminal domain, a conclusion s upported by the observation of significant sequence similarity between this region of the molecule and various members of the tropomyosin fa mily. Mutagenesis and expression studies indicate that the putative co iled-coil domain is required for association with the cytoplasmic face of the nuclear pore complex, whereas it is the NH2-terminal region of Nup84 that contains the site of interaction with CAN/Nup214. These fi ndings suggest a model in which Nup84 may function in the attachment o f CAN/Nup214 to the central framework of the nuclear pore complex, In this way, Nup84 could play a central role in the organization of the i nterface between the pore complex and the cytoplasm.