ThiI is a cytosolic, bifunctional sulfur-transfer enzyme. Its main activity is tRNA-uracil-4 sulfurtransferase: it installs 4-thiouridine (s4U) at position 8 of tRNA, the modification that makes tRNA a near-UV photosensor. The cysteine desulfurase IscS mobilizes sulfur from L-cysteine and passes it as a persulfide to ThiI. ThiI uses Mg-ATP to adenylate U8 through its PP-loop (AANH) pyrophosphatase domain, and transfers the sulfur through a persulfide on Cys456 in its C-terminal rhodanese-like domain; Cys344 and Cys456 form a disulfide during turnover. The N-terminal THUMP and ferredoxin-like domains bind the tRNA acceptor stem. The minimal substrate is a mini-helix of the stacked acceptor and T stems with a bulge starting at the target uridine; no primary sequence outside U8 is recognized. ThiI is also required for thiamin biosynthesis: without it, the sulfur carrier ThiS is not converted to ThiS-thiocarboxylate, the sulfur donor for the thiazole moiety. Work in Salmonella shows that the rhodanese domain alone suffices for this thiazole role, which is mechanistically separate from s4U synthesis.
Definition: Catalysis of the reaction: [ThiS sulfur-carrier protein]-C-terminal Gly-Gly-AMP + S-sulfanyl-L-cysteinyl-[cysteine desulfurase] + AH2 = [ThiS sulfur-carrier protein]-C-terminal-Gly-aminoethanethioate + L-cysteinyl-[cysteine desulfurase] + A + AMP + 2 H+.
Justification: The second ThiI reaction (RHEA:43340) has no GO term; GOA can only say sulfurtransferase activity. The same proposal is in genes/PSEPK/thiI.
Parent term: sulfurtransferase activity
Supporting Evidence:
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000049 tRNA binding | IEA GO_REF:0000104 | KEEP AS NON CORE | Summary: ThiI binds unmodified tRNA through its N-terminal THUMP/ferredoxin-like domains; substrate binding, not the catalytic function. Reason: tRNA binding is shown directly for E. coli ThiI by gel shift and protease protection, and the N-terminal domain is mapped as the acceptor-stem binding module. It is true but subsidiary to the sulfurtransferase activity that acts on the bound tRNA. Supporting Evidence: PMID:10753862 using gel shift and protease protection assays, we show that ThiI binds to unmodified E. coli tRNA(Phe) PMID:19509301 the N-domain can bind with both tRNA(Phe) and TPHE39A, whereas the C-domain cannot |
| GO:0002937 tRNA 4-thiouridine biosynthesis | EXP PMID:9592144 Identification of a gene involved in the generation of 4-thi... | ACCEPT | Summary: Core process; thiI was identified genetically and biochemically as the s4U8 gene. Reason: Mueller et al. identified thiI by genetic screening as required for converting U8 to s4U and confirmed the role biochemically. ThiI catalyses the final sulfur-transfer step, so it performs part of the process. Supporting Evidence: PMID:9592144 A gene involved in the conversion of uridine at position 8 into 4-thiouridine has been identified by genetic screening and its role in 4-thiouridine generation has been confirmed biochemically |
| GO:0002937 tRNA 4-thiouridine biosynthesis | IBA GO_REF:0000033 | ACCEPT | Summary: Core process, inherited across the ThiI family; E. coli ThiI is itself one of the experimental seeds. Reason: Consistent with the EXP and IMP rows. P77718 appearing in WITH/FROM marks experimental grounding on the target itself, and s4U8 synthesis is conserved in ThiI orthologs lacking the rhodanese domain (B. subtilis), so the node placement for this term is sound. Supporting Evidence: PMID:15037613 IscS catalyzes sulfur transfer from l-cysteine to ThiI, which utilizes Mg-ATP to activate uridine 8 in tRNA and transfers sulfur to give s4U |
| GO:0002937 tRNA 4-thiouridine biosynthesis | IMP PMID:7007049 4-Thiouridine triggers both growth delay induced by near-ult... | ACCEPT | Summary: The nuv mutant lacking tRNA s4U; later mapped to thiI. Reason: The cached abstract describes a nuv mutant completely lacking tRNA s4U but does not name the gene; the curator's attribution to thiI follows Mueller et al. (PMID:9592144), who identified thiI as the s4U gene. Consistent with the other rows for this term. Supporting Evidence: PMID:7007049 One mutant exhibiting a complete lack of 4-thiouridine in its tRNAs has been characterized |
| GO:0003723 RNA binding | IEA GO_REF:0000002 | MODIFY | Summary: Correct but general; the bound RNA is tRNA. Reason: The THUMP-domain mapping is right that ThiI binds RNA, but the substrate is specifically tRNA, a term the gene already carries (GO:0000049). Proposed replacements: tRNA binding Supporting Evidence: PMID:10753862 ThiI binds to unmodified E. coli tRNA(Phe) |
| GO:0004810 CCA tRNA nucleotidyltransferase activity | IEA GO_REF:0000002 | REMOVE | Summary: Wrong activity from a mis-mapped InterPro entry; ThiI does not add CCA to tRNA. Reason: IPR020536 is the ThiI AANH (PP-loop pyrophosphatase) domain, which adenylates U8 as the first half of 4-thiouridine synthesis. It shares the ATP-pyrophosphatase chemistry of CCA-adding enzymes but not their reaction (nucleotide addition to the tRNA 3' end). No study reports CCA-adding activity for ThiI. The correct activity, GO:0140741, is already on the gene from EC2GO and RHEA. Supporting Evidence: PMID:10595545 ThiI catalyzes the adenylation of a substrate at the expense of ATP PMID:15037613 ThiI, which utilizes Mg-ATP to activate uridine 8 in tRNA and transfers sulfur to give s4U |
| GO:0005515 protein binding | IPI PMID:20404999 Structural basis for Fe-S cluster assembly and tRNA thiolati... | REMOVE | Summary: Bare protein binding to IscS (P0A6B7), the sulfur donor; uninformative. Reason: Removed under the protein-binding policy as uninformative. The interaction is real: IscS delivers persulfide sulfur to ThiI, and the paper maps the ThiI interface on IscS. That relationship is already captured by the sulfurtransferase complex rows and the core sulfurtransferase activity. Supporting Evidence: PMID:20404999 direct transfer of sulfur from IscS to the acceptor ThiI leads to the s4U8 modification |
| GO:0005524 ATP binding | IEA GO_REF:0000104 | KEEP AS NON CORE | Summary: ATP is the adenylation cosubstrate; true but mechanistic detail. Reason: ThiI consumes ATP to adenylate U8, and ATP protects ThiI from active-site alkylation. ATP binding is part of the core activity rather than a separate function. Supporting Evidence: PMID:10753862 Both ATP and tRNA can protect ThiI from I-AEDANS inhibition |
| GO:0005737 cytoplasm | IEA GO_REF:0000120 | MODIFY | Summary: Correct but general; ThiI is in the cytosol. Reason: The gene already carries cytosol (GO:0005829) from a cytosol proteomics study, and its substrates (tRNA, IscS, ThiS) are soluble cytosolic components. Proposed replacements: cytosol |
| GO:0005829 cytosol | IDA PMID:18304323 Protein abundance profiling of the Escherichia coli cytosol. | ACCEPT | Summary: Detected in E. coli cytosol proteomics. Reason: Whole-cytosol abundance profiling; ThiI is not named in the cached text (the data are in supplementary tables), so the curator's reading is accepted. The location fits a soluble tRNA-modifying enzyme. Supporting Evidence: PMID:18304323 Protein abundance profiling of the Escherichia coli cytosol |
| GO:0009228 thiamine biosynthetic process | IMP PMID:9632726 Thiamin biosynthesis in Escherichia coli. Identification of ... | ACCEPT | Summary: thiI is required for ThiS thiocarboxylate formation and thiazole synthesis in E. coli. Reason: ThiS from a thiI- strain lacks the C-terminal thiocarboxylate that donates sulfur to the thiazole ring. ThiI supplies that sulfur, so it does part of the work. GO:0052837 thiazole biosynthetic process is the more specific step, but it is not an is_a or part_of descendant of thiamine biosynthesis in GO, so both stand. Supporting Evidence: PMID:9632726 The thiI gene plays an essential role in the formation of the thiocarboxylate because ThiS isolated from a thiI- strain does not contain this modification |
| GO:0009228 thiamine biosynthetic process | NAS PMID:10753862 Evidence for the transfer of sulfane sulfur from IscS to Thi... | ACCEPT | Summary: Same claim as the IMP row; the paper calls ThiI a thiamin biosynthetic enzyme. Reason: Consistent with the IMP row (PMID:9632726). Supporting Evidence: PMID:10753862 the thiamin biosynthetic enzyme ThiI |
| GO:0009229 thiamine diphosphate biosynthetic process | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: Pathway-level context from UniPathway; ThiI acts in the thiazole branch. Reason: True for E. coli, which needs ThiI for thiazole and hence thiamine diphosphate. It is the pathway endpoint rather than ThiI's step, and the thiamine and thiazole rows already state the role. Supporting Evidence: PMID:9632726 ThiFSGH and ThiI are required for the biosynthesis of the thiazole moiety of thiamin in Escherichia coli |
| GO:0009589 detection of UV | NAS PMID:10753862 Evidence for the transfer of sulfane sulfur from IscS to Thi... | MARK AS OVER ANNOTATED | Summary: s4U in tRNA is the near-UV chromophore; ThiI makes it but does not detect UV. Reason: The photosensor is the 4-thiouridine residue in tRNA, not the ThiI protein. ThiI is necessary for the response because it makes the chromophore, but it performs no step of light detection. The cited abstract does not mention UV. Supporting Evidence: PMID:7007049 4-Thiouridine, a rare nucleoside present in Escherichia coli tRNAs, has been recently proposed to be the major chromophore leading to near-ultraviolet (315-400-nm)-induced growth delay |
| GO:0016783 sulfurtransferase activity | IBA GO_REF:0000033 | MODIFY | Summary: Correct but general for the tRNA reaction; it remains the only GO term for the ThiS reaction. Reason: ThiI has two sulfurtransferase reactions. Sulfur transfer to tRNA U8 has a specific term already on the gene (GO:0140741). Sulfur transfer to ThiS (RHEA:43340) has no specific term; it is proposed below as a new term, with GO:0016783 as its parent. Propagation Review Root cause: TERM SCOPING PROBLEM Sources checked: PANTHER:PTN001804941 · PANTHER:PTN001804941 SUPPORTS TRANSFER ThiI family node; sulfurtransferase activity is correct for the family but broader than the tRNA reaction the target is known to catalyse. UniProtKB:P77718 · UniProtKB:P77718 SUPPORTS TRANSFER The target's own experimental annotation (PMID:10753862) is among the descendant evidence. Proposed replacements: tRNA-uracil-4 sulfurtransferase activity ThiS sulfur-carrier protein sulfurtransferase activity Supporting Evidence: PMID:10753862 ThiI is a recipient of S(0) from IscS and catalyzes the ultimate sulfur transfer step in the biosynthesis of s(4)U |
| GO:0016783 sulfurtransferase activity | IDA PMID:10753862 Evidence for the transfer of sulfane sulfur from IscS to Thi... | MODIFY | Summary: Direct evidence for sulfur transfer from IscS persulfide via ThiI to tRNA. Reason: Same claim as the IBA row; the assay is the tRNA s4U reaction, whose specific term is GO:0140741. Proposed replacements: tRNA-uracil-4 sulfurtransferase activity ThiS sulfur-carrier protein sulfurtransferase activity Supporting Evidence: PMID:10753862 the sulfane sulfur generated by IscS is transferred sequentially to ThiI and then to tRNA during the in vitro synthesis of s(4)U |
| GO:0016783 sulfurtransferase activity | IEA GO_REF:0000120 | MODIFY | Summary: Same claim as the IBA and IDA rows. Reason: Consistent with the other GO:0016783 rows. Proposed replacements: tRNA-uracil-4 sulfurtransferase activity ThiS sulfur-carrier protein sulfurtransferase activity |
| GO:0019448 L-cysteine catabolic process | IDA PMID:10753862 Evidence for the transfer of sulfane sulfur from IscS to Thi... | MARK AS OVER ANNOTATED | Summary: IscS, not ThiI, breaks down L-cysteine; ThiI receives the resulting sulfur. Reason: The step that consumes L-cysteine (to L-alanine plus persulfide sulfur) is catalysed by the cysteine desulfurase IscS. ThiI is the downstream acceptor of that sulfur. L-cysteine is the sulfur source for s4U, which is why the assay needs it, but ThiI does not take part in L-cysteine catabolism. Not removed, as the full text has not been read. Supporting Evidence: PMID:10753862 The enzyme converts L-cysteine to L-alanine and sulfane sulfur (S(0)) in the form of a cysteine persulfide in its active site |
| GO:0034227 tRNA thio-modification | IEA GO_REF:0000120 | MODIFY | Summary: Correct parent of the specific process the gene already carries. Reason: GO:0002937 tRNA 4-thiouridine biosynthesis is_a GO:0034227 and is supported experimentally for this gene. Proposed replacements: tRNA 4-thiouridine biosynthesis |
| GO:0044272 sulfur compound biosynthetic process | IEA GO_REF:0000117 | MODIFY | Summary: Very general; the specific sulfur-compound process is thiazole biosynthesis. Reason: GO:0052837 thiazole biosynthetic process is_a GO:0044272 and is supported for this gene. GO:0002937 tRNA 4-thiouridine biosynthesis is not a descendant of GO:0044272 (its only parent is GO:0034227 tRNA thio-modification; go-basic 2026-07-26 and QuickGO, checked 2026-11-11), so it is not a second replacement. Proposed replacements: thiazole biosynthetic process |
| GO:0052837 thiazole biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: Second core role in E. coli; ThiI supplies the sulfur for the thiazole ring via ThiS. Reason: Supported for E. coli by the thiI- phenotype (no ThiS thiocarboxylate). The IBA node is placed too broadly for rhodanese-less ThiI (see the B. subtilis review), but E. coli ThiI has the rhodanese domain that is necessary and sufficient for thiazole synthesis in Salmonella. Supporting Evidence: PMID:9632726 ThiFSGH and ThiI are required for the biosynthesis of the thiazole moiety of thiamin in Escherichia coli PMID:21724998 the C-terminal rhodanese domain of ThiI was sufficient for thiazole synthesis in vivo |
| GO:0052837 thiazole biosynthetic process | IEA GO_REF:0000002 | ACCEPT | Summary: Same claim as the IBA row, from the thiazole-specific C-terminal signature. Reason: IPR026340 / TIGR04271 mark the rhodanese-containing ThiI that supports thiazole synthesis; consistent with the IBA row. Supporting Evidence: PMID:21724998 the C-terminal rhodanese domain of ThiI was sufficient for thiazole synthesis in vivo |
| GO:0097163 sulfur carrier activity | IDA PMID:10753862 Evidence for the transfer of sulfane sulfur from IscS to Thi... | MARK AS OVER ANNOTATED | Summary: The Cys456 persulfide is a catalytic intermediate of the sulfurtransferase, not a carrier function. Reason: ThiI does covalently hold the sulfur as a persulfide before passing it to tRNA, which matches the wording of the definition. But that persulfide is the sulfurtransferase's own catalytic intermediate, as in rhodanese, and the sulfur goes onto tRNA in the same catalytic cycle. Carrier activity describes proteins such as ThiS and TusA that shuttle sulfur between enzymes. The activity is captured by GO:0140741. Supporting Evidence: PMID:10722656 Cys-456 of ThiI aligns with the active site cysteine residue of rhodanese that transiently forms a persulfide during catalysis |
| GO:0140741 tRNA-uracil-4 sulfurtransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Core molecular function. Reason: ThiI catalyses U8 adenylation and sulfur transfer from IscS persulfide to give s4U in tRNA (EC 2.8.1.4, RHEA:24176). The reaction is shown directly for E. coli ThiI, and the active-site Cys456 and the PP-loop residues are established by mutagenesis. Supporting Evidence: PMID:15037613 IscS catalyzes sulfur transfer from l-cysteine to ThiI, which utilizes Mg-ATP to activate uridine 8 in tRNA and transfers sulfur to give s4U PMID:10722656 the C456A ThiI is incapable of supporting generation of 4-thiouridine in tRNA both in vitro and in vivo file:ECOLI/thiI/thiI-uniprot.txt Cysteine persulfide intermediate |
| GO:1990221 L-cysteine desulfurase complex | IPI PMID:10753862 Evidence for the transfer of sulfane sulfur from IscS to Thi... | KEEP AS NON CORE | Summary: Transient IscS-ThiI sulfur-transfer complex. Reason: GO:1990221 is defined by what the complex does (cysteine desulfurase activity), and the IscS-ThiI heterocomplex, which ComplexPortal records with ThiI as a subunit, does that while handing the persulfide directly to ThiI. The IscS interface for ThiI is mapped (PMID:20404999). The annotation is correct; it is non-core because ThiI's own activity is the downstream sulfur transfer, not the desulfuration. Supporting Evidence: PMID:20404999 direct transfer of sulfur from IscS to the acceptor ThiI leads to the s4U8 modification |
| GO:1990228 sulfurtransferase complex | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Desulfurase-ThiI sulfur-relay complex, conserved in the family. Reason: Consistent with the IPI row. The partner differs by lineage (IscS here, NifZ in B. subtilis), but a desulfurase-ThiI relay is conserved. Supporting Evidence: PMID:10753862 the sulfane sulfur generated by IscS is transferred sequentially to ThiI and then to tRNA |
| GO:1990228 sulfurtransferase complex | IPI PMID:10753862 Evidence for the transfer of sulfane sulfur from IscS to Thi... | KEEP AS NON CORE | Summary: IscS-ThiI sulfur-relay complex. Reason: Consistent with the IBA row; a transient complex, peripheral to the catalytic function. Supporting Evidence: PMID:10753862 the sulfane sulfur generated by IscS is transferred sequentially to ThiI and then to tRNA |
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Download this section (compressed HTML)Q: Does E. coli ThiI transfer sulfur to ThiS through the same Cys456 persulfide used for s4U, or through a separate path, as the Salmonella separation-of-function mutants suggest?
Experiment: Separation-of-function E. coli thiI alleles (PP-loop versus rhodanese Cys456), scoring tRNA s4U by LC-MS and ThiS-thiocarboxylate by mass spectrometry.
Type: mutant analysis
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