The Biosynthesis of 4-Thiouridylate

A paradigm for biological sulfur transfers via persulfide groups: a persulfide–disulfide–thiol cycle in 4-thiouridine biosynthesis

“…The establishment of the fundamental features of sulfur transfer by ThiI in s 4 U generation will also inform experiments to elucidate its role in thiamine biosynthesis. 8,9,18,19 The presented evidence for the persulfidedisulfide-thiol cycle at Cys-456 of ThiI, then, confirms the shared features of sulfur transfer in the mechanisms proposed for s 4 U generation (Fig. 1) and provides a paradigm for the study of sulfur incorporation processes in other metabolic pathways.…”

“…Many bacteria convert uridine-8 in tRNA to 4-thiouridine, s 4 U, which serves as a photosensor. In tRNA, the s 4 U lies next to cytidine-13, and the two bases become cross-linked by a photoinduced 2 + 2 cycloaddition when the bacterium is exposed to near-UV light.…”

“…The cells enter growth arrest until the near-UV exposure ends and newly made tRNA (not cross-linked) can support renewed protein synthesis. The free amino acid cysteine serves as the overall sulfur donor for s 4 U biosynthesis, 4 and the reaction requires ATP. 5 The two enzymes responsible for converting uridine to s 4 U are ThiI 6 and IscS, 7 named for their roles in the biosynthesis of thiamin 8,9 and iron-sulfur clusters, 10 two physiologically critical cofactors that contain sulfur.…”

“…To test this hypothesis more fully, several controls were performed. First, when IscS is omitted from the pre-loading reaction, the spin column eluate cannot support s 4 U generation † Electronic supplementary information (ESI) available: complete experimental details. See http://www.rsc.org/suppdata/cc/b2/b208626c/ ‡ Current address: Department of Biology, New York University, New York, New York 10003, USA.…”

Sulfur-deficient transfer ribonucleic acid. Natural substrate for ribonucleic acid sulfurtransferase from Escherichia coli

“…In these early studies normal tRNA was used as the substrate for sulfur acceptance. An enzyme system which catalyzes this transfer of sulfur was recently purified from both Bacillus subtilis and from E. coli (Wong et al, 1970;Abrell et al, 1971). In both these investigations, normal tRNA was used as the primary substrate despite its presumably being fully thiolated.…”