Open AccessNucleocytoplasmic transport of ribosomes in a eukaryotic system: is there a facilitated transport process?
Author(s) -
Arati Khanna-Gupta,
Vassie C. Ware
Publication year - 1989
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.86.6.1791
Subject(s) - ribosome , biology , eukaryotic small ribosomal subunit , microbiology and biotechnology , eukaryotic ribosome , cytoplasm , protein subunit , eukaryotic large ribosomal subunit , xenopus , ran , nuclear pore , nuclear transport , biochemistry , cell nucleus , rna , gene
We have examined the kinetics of the process by which ribosomes are exported from the nucleus to the cytoplasm using Xenopus laevis oocytes microinjected into the germinal vesicle with radiolabeled ribosomes or ribosomal subunits from X. laevis, Tetrahymena thermophila, or Escherichia coli. Microinjected eukaryotic mature ribosomes are redistributed into the oocyte cytoplasm by an apparent carrier-mediated transport process that exhibits saturation kinetics as increasing amounts of ribosomes are injected. T. thermophila ribosomes are competent to traverse the Xenopus nuclear envelope, suggesting that the basic mechanism underlying ribosome transport is evolutionarily conserved. Microinjected E. coli ribosomes are not transported in this system, indicating that prokaryotic ribosomes lack the "signals" required for transport. Surprisingly, coinjected small (40S) and large (60S) subunits from T. thermophila are transported significantly faster than individual subunits. These observations support a facilitated transport model for the translocation of ribosomal subunits as separate units across the nuclear envelope whereby the transport rate of 60S or 40S subunits is enhanced by the presence of the partner subunit. Although the basic features of the transport mechanism have been preserved through evolution, other aspects of the process may be mediated through species-specific interactions. We hypothesize that a species-specific nuclear 40S-60S subunit association may expedite the transport of individual subunits across the nuclear envelope.