Ubiquitin-related modifier Urm1 acts as a sulphur carrier in thiolation of eukaryotic transfer RNA

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Ubiquitin-like proteins (UBLs) can change protein function, localization or turnover by covalent attachment to lysine residues1. Although UBLs achieve this conjugation through an intricate enzymatic cascade, their bacterial counterparts MoaD and ThiS function as sulphur carrier proteins2,3. Here we show that Urm1p, the most ancient UBL3, acts as a sulphur carrier in the process of eukaryotic transfer RNA (tRNA) modification, providing a possible evolutionary link between UBL and sulphur transfer. Moreover, we identify Uba4p, Ncs2p, Ncs6p and Yor251cp as components of this conserved pathway. Using in vitro assays, we show that Ncs6p binds to tRNA, whereas Uba4p first adenylates and then directly transfers sulphur onto Urm1p. Finally, functional analysis reveals that the thiolation function of Urm1p is critical to regulate cellular responses to nutrient starvation and oxidative stress conditions, most likely by increasing translation fidelity.

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Figure 1: Urm1p and Uba4p are functionally linked to the elongator complex.
Figure 2: Cytoplasmic tRNAs from urm1 Δ and uba4 Δ cells are not thiolated.
Figure 3: Ncs2p, Ncs6p and Yor251cp function in the URM1 pathway.
Figure 4: Urm1p acts as a sulphur carrier.


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We thank C. Rupp for technical support, M. Sohrmann for yeast strains, G. Rabut for the gift of the pGR51 plasmid, G. L. Igloi and K.-H. Altmann for providing APM, S. Mitani for tut-1(tm1297), B. Casado-Fernandez and D. Hilvert for discussion and technical advice, and T. Kurz and J. D. Alfonzo for reading the manuscript. This work was supported by grants from EuroDyna (to S.L.), the Roche Research Foundation (to P.G.A.P.), ETHZ (to S.L. and M.P.), the SNF (to M.P.), the Canadian Institutes of Health Research (to C.B.) and Genome Canada through the Ontario Genomics Institute (to C.B.).

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Correspondence to Kay Hofmann or Matthias Peter.

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Leidel, S., Pedrioli, P., Bucher, T. et al. Ubiquitin-related modifier Urm1 acts as a sulphur carrier in thiolation of eukaryotic transfer RNA. Nature 458, 228–232 (2009) doi:10.1038/nature07643

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