During Aspergillus nidulans closed mitosis, the nuclear pore complex (NPC) is partially disassembled, facilitating nuclear entry of tubulin and mitotic regulators (De Souza et al. 2004. Current Biology 14:1973-84). Genetic, overexpression and localization studies all implicate the NIMA mitotic kinase in regulating partial NPC disassembly during mitosis. We hypothesize that NIMA triggers the mitotic dispersal of the SONA and SONBn NPC proteins (nucleoporins) from the NPC as the first step in mitotic NPC disassembly. The SONBc structural nucleoporin remains associated with the nuclear envelope throughout mitosis. SONA and SONBn bind each Nup96 other and are likely tethered to the NPC by binding of SONBn to SONBc . Nup96 To define how the initial steps in mitotic NPC disassembly are regulated, we have determined the minimal domain within SONBn required for binding to the NPC. We demonstrate that this domain (SONBn ) disperses from the NPC during mitosis and is 587-1035 mitotically phosphorylated in a NIMA-dependent manner. SONBn contains 8 consensus NIMA phosphorylation sites and we 587-1035 demonstrate that mutation of all eight sites to glutamic acid compromises binding to the NPC. To determine if these sites (or other sites) are phosphorylated in vivo, we have generated an S-tagged version of SONBn allowing single step purification using S-protein 587-1035 agarose. S-tag-SONBn has been purified to homogeneity from mitotic A. nidulans extracts to facilitate the identification of 587-1035 phosphorylated residues utilizing mass spectrometry. Similar strategies are being employed to determine the sites of mitotic phosphorylation in SONBc Nup96.
Full conference title:
23rd Fungal Genetics Conference
- Fungal Genetics Conference 23rd (2002)