Coordinated nuclear export of 60S ribosomal subunits and NMD3 in vertebrates.
60S and 40S ribosomal subunits are assembled in the nucleolus and exported from the nucleus to the cytoplasm independently of each other. We show that in vertebrate cells, transport of both subunits requires the export receptor CRM1 and Ran.GTP. Export of 60S subunits is coupled with that of the nucleo- cytoplasmic shuttling protein NMD3. Human NMD3 (hNMD3) contains a CRM-1-dependent leucine-rich nuclear export signal (NES) and a complex, dispersed nuclear localization signal (NLS), the basic region of which is also required for nucleolar accumulation. When present in Xenopus oocytes, both wild-type and export-defective mutant hNMD3 proteins bind to newly made nuclear 60S pre-export particles at a late step of subunit maturation. The export-defective hNMD3, but not the wild-type protein, inhibits export of 60S subunits from oocyte nuclei. These results indicate that the NES mutant protein competes with endogenous wild-type frog NMD3 for binding to nascent 60S subunits, thereby preventing their export. We propose that NMD3 acts as an adaptor for CRM1-Ran.GTP-mediated 60S subunit export, by a mechanism that is conserved from vertebrates to yeast.
Trotta
Christopher R
CR
Department of Biomolecular Chemistry, University of Wisconsin Medical School, 1300 University Avenue, Madison, WI 53706, USA.
Lund
Elsebet
E
Kahan
Lawrence
L
Johnson
Arlen W
AW
Dahlberg
James E
JE
D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D000818:Animals; D001667:Binding, Competitive; D017124:Conserved Sequence; D005260:Female; D006367:HeLa Cells; D006801:Humans; D066298:In Vitro Techniques; D028884:Karyopherins / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D019913:Nuclear Localization Signals / Q000235:genetics; D009865:Oocytes / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D012270:Ribosomes / Q000737:chemistry / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014162:Transfection; D014982:Xenopus laevis; D020931:ran GTP-Binding Protein / Q000378:metabolism; D000097606:Exportin 1 Protein
D028884:Karyopherins; D019913:Nuclear Localization Signals; D016601:RNA-Binding Proteins; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D020931:ran GTP-Binding Protein; D000097606:Exportin 1 Protein; C475570:NMD3 protein, human