tRNAGlu wobble uridine methylation by Trm9 identifies Elongator's key role for zymocin‐induced cell death in yeast

Summary Zymocin-induced cell death in Saccharomyces cerevisiae requires the toxin-target (TOT) effector Elongator, a protein complex with functions in transcription, exocytosis and tRNA modification. In line with the latter, trm9Δ cells lacking a tRNA methylase specific for wobble uridine (U34) residues survive zymocin and in excess, the Trm9 substrate tRNAGlu copies zymocin protection of Elongator mutants. Phenotypes typical of a tot3/elp3Δ Elongator mutant are absent from trm9Δ cells but copied in a tot3Δtrm9Δ double mutant suggesting that Elongator acts upstream of Trm9. Consistent with Elongator-dependent tRNA modification being more important to mRNA decoding than Trm9, SUP4 and SOE1TRNA suppressors are highly sensitive to loss of Elongator and tRNA U34 hypomodification. As Trm9 overexpression counteracts the effect of high-copy tRNAGlu, zymocin suppression by high-copy tRNAGlu may reflect tRNA hypomethylation of trm9Δ cells. Thus, Trm9 methylation may enable recognition of tRNA by zymocin, a notion supported by a dramatic reduction of tRNAGlu levels in zymocin-treated cells and by cytotoxic zymocin residues conserved between bacterial nucleases and a tRNA modifying GTPase. In sum, Trm9 is a bona fideTOT pathway component whose methylation may be hijacked by zymocin to target tRNA function and eventually, mRNA translation.