# Evolutionary conservation of ubiquitin-like protein urmylation as revealed by URM1 gene shuffle from archaea to yeast

## TL;DR

This study shows that Urm1, a protein involved in sulfur transfer and protein modification, has conserved functions across archaea and yeast, revealing its evolutionary significance.

## Contribution

The study demonstrates functional separation of Urm1's roles in tRNA thiolation and urmylation through cross-species gene transfer.

## Key findings

- Archaeal Urm1 conjugates to yeast peroxiredoxin Ahp1 but cannot support tRNA thiolation.
- Thioactivation of archaeal Urm1 and urmylation-like conjugation are conserved between Sulfolobus and Saccharomyces.
- Urm1's dual roles in sulfur transfer and protein modification can be functionally separated in yeast.

## Abstract

Urm1 from yeast is a unique ubiquitin-like protein with dual functionality. It has been shown to operate in tRNA thiolation and protein urmylation, combining features typical of bacterial sulfur carriers and classical ubiquitin-like modifiers. Hence, in evolutionary terms, Urm1 may be placed at the crossroad of prokaryotic sulfur transfer and eukaryotic protein conjugation pathways. Prompted by Urm1-like proteins identified in Archaea, we examined Urm1 functional conservation using URM1 gene shuffle from Sulfolobus acidocaldarius to Saccharomyces cerevisiae. We find that archaeal Urm1 conjugates to peroxiredoxin Ahp1, a bona fide urmylation target in yeast, but cannot support tRNA thiolation. Ahp1 conjugation requires sulfur transfer onto the archaeal Urm1 modifier from Uba4, the E1-like urmylation activator in yeast. Thus, thioactivation of archaeal Urm1 and urmylation-like conjugation are conserved and exchangeable processes between Sulfolobus and Saccharomyces. Our survey underlines that Urm1 likely occupies a key role in the evolution of the ubiquitin-like protein family.

URM1 gene shuffle from S. acidocaldarius to S. cerevisiae has uncovered that dual-functional sulfur carrier roles for Urm1 in tRNA thiolation and protein urmylation can be separated from one another by expressing an archaeal Urm1 homolog in yeast.