Characterization of the nucleocytoplasmic export of tRNA in Saccharomyces cerevisiae
In 'Saccharomyces cerevisiae' Los1p facilitates tRNA translocation through the nuclear pore complex whereas Arc1p delivers translocated tRNAs to their cognate aminoacyl-tRNA synthetases. Mutation of nucleotide C11 in an amber suppressor tyrosine tRNA (Tyram ) resulted in its nuclear retention. This is not due to gross alteration of the tRNA structure. The mutation also did not affect transcription or processing. Expression of Los1p or complementary mutation at position 24 can rescue nuclear export of the Tyram mutant. This implies that the conformation of nucleotide 11 is important for the interaction between the tRNA and its export receptors. tRNA exportins, 'TEX1' and 'TEX2', were identified as interacting with tRNA by a yeast three-hybrid system. Tex1p is a nuclear protein similar to Los1p whereas Tex2p is a cytoplasmic protein similar to importin-[beta]. Both proteins can rescue a nuclear export-defective Tyram mutant, which implies that Tex1p and Tex2p are involved in the nuclear tRNA export process.