Impaired tRNA Nuclear Export Links DNA Damage and Cell-Cycle Checkpoint

Abstract

In response to genotoxic stress, cells evoke a plethora of physiological responses collectively aimed at enhancing viability and maintaining the integrity of the genome. Here, we report that unspliced tRNA rapidly accumulates in the nuclei of yeast Saccharomyces cerevisiae after DNA damage. This response requires an intact MEC1- and RAD53-dependent signaling pathway that impedes the nuclear export of intron-containing tRNA via differential relocalization of the karyopherin Los1 to the cytoplasm. The accumulation of unspliced tRNA in the nucleus signals the activation of Gcn4 transcription factor, which, in turn, contributes to cell-cycle arrest in G1 in part by delaying accumulation of the cyclin Cln2. The regulated nucleocytoplasmic tRNA trafficking thus constitutes an integral physiological adaptation to DNA damage. These data further illustrate how signal-mediated crosstalk between distinct functional modules, namely, tRNA nucleocytoplasmic trafficking, protein synthesis, and checkpoint execution, allows for functional coupling of tRNA biogenesis and cell-cycle progression.

Maf1 Protein, Repressor of RNA Polymerase III, Indirectly Affects tRNA Processing

“…We explored the possibility that growth in glycerol medium may influence expression or localization of Los1. It has been previously reported that Los1 is mislocalized to cytoplasm upon DNA damage, causing increased nuclear accumulation of intron-containing tRNA (47). We therefore examined localization of C-terminally Myc-tagged Los1 in control and maf1⌬ cells grown under standard (YPD) or restrictive (YPGly, 37°C) conditions (Fig.…”

“…Induction of Gcn4 Expression in maf1⌬ Cells-Both aberrant tRNA processing and limited tRNA export have marked effects upon the translation of the transcription factor, Gcn4 (47,48). Conditions that activate Gcn4 reduce the rate of general protein synthesis while simultaneously activating expression of proteins required under conditions of starvation and stress (reviewed in Ref.…”

Looking at membrane lipids from the inside of the cell

“…While nature chose to link decoding to anticodon modification and codon usage in this yeast stress response, the possibility that other tRNA-related activities may be involved in other systems should be suspected. Of note are reports that alterations to tRNA processing, modification and subcellular transport can signal or result from stress, including MMS, nutrient deprivation and Elongator-sensitive zymocin toxicity 4,5,[9][10][11] . Although the chemical state of U34 and the decoding capacity of hypomodified tRNA Arg UCU and tRNA Glu UUC in trm9-∆ cells remain to be determined, the results point to exciting new means of genetic control.…”

“…Although the chemical state of U34 and the decoding capacity of hypomodified tRNA Arg UCU and tRNA Glu UUC in trm9-∆ cells remain to be determined, the results point to exciting new means of genetic control. It will be interesting to know whether changes in the relative amount and/or decoding capacity of other subsets of tRNAs-as can occur via alterations in tRNA splicing, transport, modification or other processes [9][10][11] -are keyed to codon usage.…”

“…1c) 4,5,[9][10][11] . Although the chemical state of U34 and the decoding capacity of hypomodified tRNA Arg UCU and tRNA Glu UUC in trm9-∆ cells remain to be determined, the results point to exciting new means of genetic control.…”