Formation of thiolated nucleosides present in tRNA from Salmonella enterica serovar Typhimurium occurs in two principally distinct pathways

J Bacteriol. 2004 Feb;186(3):758-66. doi: 10.1128/JB.186.3.758-766.2004.


tRNA from Salmonella enterica serovar Typhimurium contains five thiolated nucleosides, 2-thiocytidine (s(2)C), 4-thiouridine (s(4)U), 5-methylaminomethyl-2-thiouridine (mnm(5)s(2)U), 5-carboxymethylaminomethyl-2-thiouridine (cmnm(5)s(2)U), and N-6-(4-hydroxyisopentenyl)-2-methylthioadenosine (ms(2)io(6)A). The levels of all of them are significantly reduced in cells with a mutated iscS gene, which encodes the cysteine desulfurase IscS, a member of the ISC machinery that is responsible for [Fe-S] cluster formation in proteins. A mutant (iscU52) was isolated that carried an amino acid substitution (S107T) in the IscU protein, which functions as a major scaffold in the formation of [Fe-S] clusters. In contrast to the iscS mutant, the iscU52 mutant showed reduced levels of only two of the thiolated nucleosides, ms(2)io(6)A (10-fold) and s(2)C (more than 2-fold). Deletions of the iscU, hscA, or fdx genes from the isc operon lead to a similar tRNA thiolation pattern to that seen for the iscU52 mutant. Unexpectedly, deletion of the iscA gene, coding for an alternative scaffold protein for the [Fe-S] clusters, showed a novel tRNA thiolation pattern, where the synthesis of only one thiolated nucleoside, ms(2)io(6)A, was decreased twofold. Based on our results, we suggest two principal distinct routes for thiolation of tRNA: (i) a direct sulfur transfer from IscS to the tRNA modifying enzymes ThiI and MnmA, which form s(4)U and the s(2)U moiety of (c)mnm(5)s(2)U, respectively; and (ii) an involvement of [Fe-S] proteins (an unidentified enzyme in the synthesis of s(2)C and MiaB in the synthesis of ms(2)io(6)A) in the transfer of sulfur to the tRNA.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Escherichia coli Proteins*
  • HSP70 Heat-Shock Proteins / physiology
  • Iron-Sulfur Proteins / metabolism
  • Mutation
  • Nucleosides / metabolism*
  • Operon
  • RNA, Bacterial / metabolism*
  • RNA, Transfer / metabolism*
  • Salmonella typhimurium / genetics*
  • Salmonella typhimurium / growth & development
  • Sulfhydryl Compounds / metabolism*
  • Thiouridine / metabolism


  • Escherichia coli Proteins
  • HSP70 Heat-Shock Proteins
  • Iron-Sulfur Proteins
  • Nucleosides
  • RNA, Bacterial
  • Sulfhydryl Compounds
  • hscA protein, E coli
  • Thiouridine
  • RNA, Transfer