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Proc Natl Acad Sci U S A. 2011 Jun 28;108(26):10502-7. doi: 10.1073/pnas.1105645108. Epub 2011 Jun 13.

Retrograde nuclear import of tRNA precursors is required for modified base biogenesis in yeast.

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Department of Chemistry and Biotechnology, Graduate School of Engineering, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan.


The retrograde movement of tRNAs from the cytoplasm to the nucleus occurs constitutively in eukaryotic cells but its functional significance remains unclear. We show evidence suggesting that in Saccharomyces cerevisiae, a spliced tRNA precursor must be imported into the nucleus before the biogenesis of a modified base can occur. Wybutosine (yW) is a modified base adjacent to the anticodon of tRNA(Phe) and is required for accurate decoding. Glucose starvation or overexpression of the nuclear tRNA binding protein Trz1p both caused nuclear retention of cytoplasmic tRNAs, impaired the yW synthesis, and induced the accumulation of its intermediate, N(1)-methylgunanosine (m(1)G), showing that the postspliced tRNA(Phe) is imported to the nucleus, where m(1)G is formed by Trm5p, after which it is reexported to the cytoplasm, where the yW synthesis is completed by cytoplasmic enzymes.

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