Novel interaction of the 60S ribosomal subunit export adapter Nmd3 at the nuclear pore complex.
Nuclear export of the large (60S) ribosomal subunit depends on the adapter protein Nmd3 to provide a nuclear export signal (NES). The leucine-rich NES is recognized by the export receptor Crm1 to mediate export via interaction with the nuclear pore complex (NPC). Here, we show that certain mutant Nmd3 proteins that are impaired for binding to the 60S subunit accumulate at the nuclear envelope. These mutant proteins also show enhanced binding to Crm1, both in vivo and in vitro. Although their interaction with the NPC is dependent on recognition of the NES by Crm1, their interaction with Crm1 is not strictly dependent on RanGTP. Using a collection of GFP-tagged nucleoporin mutants, we identified several nucleoporins, including components of the Nup82 complex that copurified with the mutant Nmd3. The Nup82 complex is on the cytoplasmic face of the NPC and has previously been shown to be important as a terminal binding site for Crm1-mediated export. Mutations in the Nup82 complex led to accumulation of wild-type Nmd3 in the nucleoplasm, suggesting that the interaction of mutant Nmd3 with the Nup82 complex reflects a defect in the bona fide export pathway for the 60S subunit. These results suggest that in the absence of the ribosome, Nmd3 is not efficiently released from Crm1 at the NPC.
West
Matthew
M
Section of Molecular Genetics and Microbiology and the Institute for Cellular and Molecular Biology, the University of Texas, Austin, TX 78712, USA.
Hedges
John B
JB
Lo
Kai-Yin
KY
Johnson
Arlen W
AW
D021581:Active Transport, Cell Nucleus; D003600:Cytosol / Q000378:metabolism; D028884:Karyopherins / Q000235:genetics / Q000378:metabolism*; D009685:Nuclear Envelope; D049790:Nuclear Export Signals; D022022:Nuclear Pore / Q000378:metabolism*; D021122:Protein Subunits; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000378:metabolism*; D012270:Ribosomes / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D020931:ran GTP-Binding Protein / Q000235:genetics / Q000378:metabolism; D000097606:Exportin 1 Protein
D028884:Karyopherins; D049790:Nuclear Export Signals; D021122:Protein Subunits; D016601:RNA-Binding Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D029701:Saccharomyces cerevisiae Proteins; D020931:ran GTP-Binding Protein; D000097606:Exportin 1 Protein; C117894:NMD3 protein, S cerevisiae