tRNA transport from the nucleus in a eukaryotic cell: carrier-mediated translocation process.
The mechanism by which a tRNA molecule is delivered from the nucleus of a cell to the cytoplasm has been studied in the Xenopus laevis oocyte utilizing nuclear microinjection and manual microdissection techniques. tRNA nuclear transport in this cell resembles a carrier-mediated translocation process rather than diffusion through a simple pore or channel. tRNA transport is saturable by tRNA, with a maximal rate measured to be about 190 X 10(7) molecules per min per nucleus (21 degrees C) in the mature oocyte. Competitive inhibition between two different tRNA species can be demonstrated, suggesting that many tRNA species share a common carrier system. tRNA nuclear transport is sharply dependent on temperature, with an optimal rate observed at 31 degrees C. A single G-to-U substitution at position 57 in the vertebrate tRNAMeti molecule reduces the transport rate of this tRNA by a factor of about 20, implicating this highly conserved region of the tRNA molecule (loop IV) as critical for recognition by the transport mechanism. On morphologic grounds I propose that ribosome-like components surrounding the nuclear pore may function as the tRNA translocation "motor." The tRNA nuclear transport mechanism represents a distinctly eukaryotic process and a site of potential control over cell growth and proliferation.
D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism; D002467:Cell Nucleus / Q000378:metabolism*; D007700:Kinetics; D008845:Microinjections; D012343:RNA, Transfer / Q000378:metabolism*; D013045:Species Specificity; D013696:Temperature; D014982:Xenopus laevis
D002352:Carrier Proteins; D012343:RNA, Transfer