Phosphorylation of NPA58, a rat nuclear pore-associated protein, correlates with its mitotic distribution

At the onset of mitosis in higher eukaryotic cells, the nuclear envelope an d its components including subunits of the nuclear pore complexes are disas sembled, and these are reassembled toward the end of mitosis. We have studi ed the role of protein phosphorylation in this process, by investigating th e phosphorylation status of a specific pore-associated protein during mitos is. Using a monoclonal antibody, mAb E2, earlier shown to inhibit nuclear p rotein import in rat fibroblast cells, we have identified a 58-kDa protein termed NPA58 that is partially associated with nuclear pores based on a hig h degree of coincident immunofluorescence in dual labeling experiments with mAb 414, a well-studied pore-complex-reactive antibody. NPA58 is specifica lly phosphorylated during mitosis and dephosphorylated upon release from me taphase arrest. Confocal microscopy analysis shows that NPA58 is dispersed in the cytoplasm early in mitosis when it is phosphorylated, while its relo calization in the reforming nuclear envelope during telophase temporally co rrelates with its dephosphorylation upon release from metaphase arrest. Our data provide in vivo evidence that the modifications mediated by phosphory lation and dephosphorylation are required for regulating the mitotic locali zation of a nuclear-pore-associated protein. (C) 2000 Academic Press.