Genome-Wide Investigation of the Role of the tRNA Nuclear- Cytoplasmic Trafficking Pathway in Regulation of the Yeast

In eukaryotic cells, tRNAs are transcribed and partially processed in the nucleus before they are exported to the cytoplasm, where they have an essential role in protein synthesis. Surprisingly, mature cytoplasmic tRNAs shuttle between nucleus and cy-toplasm, and tRNA subcellular distribution is nutrient dependent. At least three members of the -importin family, Los1, Mtr10, andMsn5, function in tRNA nuclear-cytoplasmic intracellular movement. To test the hypothesis that the tRNA retro-grade pathway regulates the translation of particular transcripts, we compared the expression profiles from nontranslating mR-NAs and polyribosome-associated translating mRNAs collected frommsn5,mtr10, and wild-type cells under fed or acute amino acid depletion conditions. Our microarray data revealed that the methionine, arginine, and leucine biosynthesis pathways are targets of the tRNA retrograde process. We confirmed the microarray data by Northern andWestern blot analyses. The levels of some of the particular target mRNAs were reduced, while others appeared not to be affected. However, the protein levels of all tested targets in these pathways were greatly decreased when tRNA nuclear import or reexport to the cytoplasm was disrupted. This study provides information that tRNA nuclear-cytoplasmic dynamics is connected to the biogenesis of proteins involved in amino acid biosynthesis. An essential function performed by tRNAs is the delivery ofamino acids to ribosomes to decode information in mRNAs into proteins. tRNAs are transcribed in the nucleus and then are exported to the cytoplasm, where they function in protein synthe