The enzyme, found in bacteria and archaea, is activated by EC?2.8.1.7, cysteine desulfurase, which transfers a sulfur atom to an internal?L-cysteine residue, forming a cysteine persulfide. The activated enzyme then transfers the sulfur to a uridine in a tRNA chain in a reaction that requires ATP. The enzyme from the bacterium?Escherichia coli?forms 4-thiouridine only at position 8 of tRNA. The enzyme also participates in the biosynthesis of the thiazole moiety of thiamine, but different domains are involved in the two processes.
