title: Sulfur transfer and activation by ubiquitin-like modifier system Uba4•Urm1 link protein urmylation and tRNA thiolation in yeast.
abstract: Urm1 is a unique dual-function member of the ubiquitin protein family and conserved from yeast to man. It acts both as a protein modifier in ubiquitin-like urmylation and as a sulfur donor for tRNA thiolation, which in concert with the Elongator pathway forms 5-methoxy-carbonyl-methyl-2-thio (mcm5s2) modified wobble uridines (U34) in anticodons. UsingSaccharomyces cerevisiaeas a model to study a relationship between these two functions, we examined whether cultivation temperature and sulfur supply previously implicated in the tRNA thiolation branch of theURM1pathway also contribute to proper urmylation. Monitoring Urm1 conjugation, we found urmylation of the peroxiredoxin Ahp1 is suppressed either at elevated cultivation temperatures or under sulfur starvation. In line with this, mutants with sulfur transfer defects that are linked to enzymes (Tum1, Uba4) required for Urm1 activation by thiocarboxylation (Urm1-COSH) were found to maintain drastically reduced levels of Ahp1 urmylation and mcm5s2U34 modification. Moreover, as revealed by site specific mutagenesis, the S-transfer rhodanese domain (RHD) in the E1-like activator (Uba4) crucial for Urm1-COSH formation is critical but not essential for protein urmylation and tRNA thiolation. In sum, sulfur supply, transfer and activation chemically link protein urmylation and tRNA thiolation. These are features that distinguish the ubiquitin-like modifier system Uba4•Urm1 from canonical ubiquitin family members and will help elucidate whether, in addition to their mechanistic links, the protein and tRNA modification branches of theURM1pathway may also relate in function to one another.
authors.affiliation: Universität Kassel, Institut für Biologie, FG Mikrobiologie, Heinrich-Plett-Str. 40, 34132 Kassel, Germany.
authors.forename: André
authors.initials: A
authors.lastname: Jüdes
authors.affiliation: Universität Kassel, Institut für Biologie, FG Mikrobiologie, Heinrich-Plett-Str. 40, 34132 Kassel, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Bruch
authors.affiliation: Universität Kassel, Institut für Biologie, FG Mikrobiologie, Heinrich-Plett-Str. 40, 34132 Kassel, Germany.
authors.forename: Roland
authors.initials: R
authors.lastname: Klassen
authors.affiliation: Johannes Gutenberg Universität Mainz, Institut für Pharmazie und Biochemie, Staudinger Weg 5, 55128 Mainz, Germany.
authors.forename: Mark
authors.initials: M
authors.lastname: Helm
authors.affiliation: Universität Kassel, Institut für Biologie, FG Mikrobiologie, Heinrich-Plett-Str. 40, 34132 Kassel, Germany.
authors.forename: Raffael
authors.initials: R
authors.lastname: Schaffrath
keywords: E1-like enzyme Uba4; Saccharomyces cerevisiae; protein urmylation; sulfur transferase Tum1; tRNA thiolation; tRNase zymocin; ubiquitin-like modifier Urm1