Nucleocytoplasmic transport of ribosomes in a eukaryotic system: is there a facilitated transport process?

• DOI: 10.1073/pnas.86.6.1791
• Publication Date: 2006-05-31T11:15:03Z
• Authors: A Khanna-Gupta; V C Ware
• Keywords: Eukaryotic Ribosome; Ran; Nuclear pore

We have examined the kinetics of process by which ribosomes are exported from nucleus to cytoplasm using Xenopus laevis oocytes microinjected into germinal vesicle with radiolabeled or ribosomal subunits X. laevis, Tetrahymena thermophila, Escherichia coli. Microinjected eukaryotic mature redistributed oocyte an apparent carrier-mediated transport that exhibits saturation as increasing amounts injected. T. thermophila competent traverse nuclear envelope, suggesting basic mechanism underlying ribosome is evolutionarily conserved. E. coli not transported in this system, indicating prokaryotic lack "signals" required for transport. Surprisingly, coinjected small (40S) and large (60S) significantly faster than individual subunits. These observations support a facilitated model translocation separate units across envelope whereby rate 60S 40S enhanced presence partner subunit. Although features been preserved through evolution, other aspects may be mediated species-specific interactions. hypothesize 40S-60S subunit association expedite envelope.