Thio-modification of yeast cytosolic tRNA requires a ubiquitin-related system that resembles bacterial sulfur transfer systems

Abstract

The wobble uridine in yeast cytosolic tRNALys2UUU and tRNAGlu3UUC undergoes a thio-modification at the second position (s2 modification) and a methoxycarbonylmethyl modification at the fifth position (mcm5 modification). We previously demonstrated that the cytosolic and mitochondrial iron-sulfur (Fe/S) cluster assembly machineries termed CIA and ISC, including a cysteine desulfurase called Nfs1, were essential for the s2 modification. However, the cytosolic component that directly participates in this process remains unclear. We found that ubiquitin-like protein Urm1 and ubiquitin-activating enzyme-like protein Uba4, as well as Tuc1 and Tuc2, were strictly required for the s2 modification. The carboxyl-terminal glycine residue of Urm1 was critical for the s2 modification, indicating direct involvement of the unique ubiquitin-related system in this process. We also demonstrated that the s 2 and mcm5 modifications in cytosolic tRNAs influence each other's efficiency. Taken together, our data indicate that the s2 modification of cytosolic tRNAs is a more complex process that requires additional unidentified components. © 2008 by The American Society for Biochemistry and Molecular Biology, Inc.