RpoH (sigma-32) is the heat shock sigma factor encoded by DVU_1584 in Desulfovibrio vulgaris Hildenborough. As a member of the sigma-70 family (Group 3), RpoH directs the RNA polymerase holoenzyme to heat shock promoters with the consensus motif aTTGAAA-[N12]-aaCTaT (Chhabra et al., 2006). RpoH functions as a cytosolic transcription initiation factor that regulates expression of heat shock genes including chaperones (GroEL, GroES, ClpB, HtpG) and proteases (ClpX) in response to proteotoxic stress conditions including heat shock, oxidative stress, and biocide exposure. The protein contains characteristic sigma-70 domains (regions 1.2, 2, and 4) essential for promoter recognition and RNA polymerase binding.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:2000142 regulation of DNA-templated transcription initiation | IEA GO_REF:0000108 | ACCEPT | Summary: RpoH regulates transcription initiation by directing RNA polymerase to heat shock promoters. The predicted rpoH promoter motif in D. vulgaris is aTTGAAA-[N12]-aaCTaT (PMID:16484192). Under heat shock and biocide stress, RpoH-regulated genes (groEL, groES, clpX, clpB, htpG) show increased expression (PMID:20437234), demonstrating regulation of transcription initiation. Reason: This annotation correctly captures the regulatory function of sigma factors. RpoH specifically regulates transcription initiation by conferring promoter specificity to the RNA polymerase holoenzyme, directing it to heat shock promoters. Evidence from D. vulgaris transcriptomics shows RpoH-dependent activation of heat shock genes under stress conditions. Supporting Evidence: PMID:16484192 promoter sequences corresponding to the alternate sigma factors sigma(32) and sigma(54) PMID:20437234 Glut induces expression of genes required to degrade or refold proteins inactivated by either chemical modification or heat shock file:DESVH/Q72BQ0/Q72BQ0-deep-research-falcon.md DVU_1584 encodes the alternative sigma factor RpoH (sigma-32), a member of the sigma-70 family mediating transcriptional responses to proteotoxic/heat and related stresses in D. vulgaris |
| GO:0003677 DNA binding | IEA GO_REF:0000120 | MODIFY | Summary: Sigma factors like RpoH do not bind DNA autonomously but confer promoter specificity to the RNA polymerase holoenzyme. The GO term definition for sigma factor activity explicitly states that sigma does not bind DNA on its own but when combined with the core to form the holoenzyme, the sigma factor binds specifically to promoter elements. Reason: While technically sigma factors enable DNA binding as part of the holoenzyme, this annotation is misleading. Sigma factors do not bind DNA independently - they require association with core RNA polymerase. The more specific and accurate annotation is GO:0016987 'sigma factor activity' which already exists in the annotation set. The DNA binding annotation is redundant and potentially misleading about the mechanism of sigma factor function. Proposed replacements: sigma factor activity Supporting Evidence: file:DESVH/Q72BQ0/Q72BQ0-deep-research-falcon.md Sigma factors are soluble, cytosolic transcription initiation factors that bind the core RNA polymerase to form holoenzyme and direct promoter recognition |
| GO:0003700 DNA-binding transcription factor activity | IEA GO_REF:0000120 | MODIFY | Summary: RpoH is a sigma factor, not a classical DNA-binding transcription factor. Sigma factors function by associating with RNA polymerase core enzyme to confer promoter specificity, then dissociating once elongation begins. This differs fundamentally from transcription factors that bind DNA regulatory elements independently and modulate transcription. Reason: This annotation conflates two distinct mechanisms of transcriptional regulation. Sigma factors do not function as conventional transcription factors - they are dissociable subunits of RNA polymerase that confer promoter recognition specificity. The GO term GO:0016987 'sigma factor activity' is the appropriate molecular function annotation for RpoH. The UniProt keywords also classify this protein as 'Sigma factor' rather than 'Transcription factor'. Proposed replacements: sigma factor activity Supporting Evidence: UniProt:Q72BQ0 -!- FUNCTION: Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released. file:DESVH/Q72BQ0/Q72BQ0-deep-research-falcon.md DVU_1584 (locus tag in Desulfovibrio vulgaris Hildenborough) encodes a sigma-70 family protein annotated as rpoH, the heat-shock sigma factor |
| GO:0006352 DNA-templated transcription initiation | IEA GO_REF:0000002 | ACCEPT | Summary: RpoH participates in transcription initiation as part of the RNA polymerase holoenzyme. When associated with core RNA polymerase, RpoH enables recognition and binding of heat shock promoters to initiate transcription of stress response genes. Evidence from D. vulgaris heat shock studies confirms involvement in transcription initiation at sigma-32 promoters (PMID:16484192). Reason: This biological process annotation is accurate for sigma factors. RpoH directly participates in DNA-templated transcription initiation by forming the holoenzyme with core RNA polymerase and enabling promoter recognition. The sigma subunit is released after promoter escape/clearance but is essential for the initiation phase. This is consistent with the InterPro-based evidence source. Supporting Evidence: PMID:16484192 promoter sequences corresponding to the alternate sigma factors sigma(32) and sigma(54) UniProt:Q72BQ0 -!- FUNCTION: Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released. |
| GO:0006355 regulation of DNA-templated transcription | IEA GO_REF:0000120 | ACCEPT | Summary: RpoH regulates transcription by directing RNA polymerase to heat shock genes under stress conditions. Transcriptomic studies in D. vulgaris demonstrate RpoH-dependent regulation of heat shock genes (groEL, groES, clpX, clpB, htpG, hrcA) during heat shock, oxidative stress, and biocide exposure (PMID:16484192; PMID:20437234; PMID:18060664). Reason: This is an appropriate biological process annotation for sigma factors. RpoH regulates transcription by determining which promoters the RNA polymerase holoenzyme recognizes. Under stress conditions, RpoH activation leads to transcription of heat shock regulon genes. Multiple D. vulgaris studies confirm this regulatory role. Supporting Evidence: PMID:20437234 Glut induces expression of genes required to degrade or refold proteins inactivated by either chemical modification or heat shock PMID:18060664 multiple genes encoding heat shock proteins, peptidases and proteins with heat shock promoters |
| GO:0016987 sigma factor activity | IEA GO_REF:0000120 | ACCEPT | Summary: RpoH (DVU_1584) is definitively a sigma factor of the sigma-70 family. UniProt classifies it as 'RNA polymerase sigma factor' with sigma factor keywords. Domain analysis confirms sigma-70 regions 1.2, 2, and 4. The D. vulgaris genome annotation identifies DVU_1584 as rpoH (heat shock sigma-32). PANTHER classification is PTHR30376:SF3 'RNA POLYMERASE SIGMA FACTOR RPOH'. Reason: This is the most accurate and specific molecular function annotation for RpoH. Sigma factor activity precisely describes the function of RpoH - conferring promoter specificity to RNA polymerase for recognition of heat shock promoters. This annotation is supported by domain architecture, protein family membership, and functional studies in D. vulgaris. Supporting Evidence: UniProt:Q72BQ0 -!- FUNCTION: Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released. ... -!- SIMILARITY: Belongs to the sigma-70 factor family. file:DESVH/Q72BQ0/Q72BQ0-deep-research-falcon.md DVU_1584 (locus tag in Desulfovibrio vulgaris Hildenborough) encodes a sigma-70 family protein annotated as rpoH, the heat-shock sigma factor |
| GO:0034605 cellular response to heat | IEA PMID:16484192 Global analysis of heat shock response in Desulfovibrio vulg... | NEW | Summary: RpoH is the canonical heat shock sigma factor that mediates the cellular response to heat in bacteria. In D. vulgaris, heat shock activates the RpoH-dependent regulon including chaperones and proteases essential for survival under thermal stress (PMID:16484192). The predicted rpoH promoter motif matches canonical sigma-32 heat shock promoters. Reason: This biological process annotation should be added as it represents a core function of RpoH. The sigma-32 (rpoH) gene product specifically mediates cellular response to heat by activating expression of heat shock proteins. This is well-documented in D. vulgaris through the global heat shock response study (PMID:16484192). Supporting Evidence: PMID:16484192 Global analysis of heat shock response in Desulfovibrio vulgaris Hildenborough file:DESVH/Q72BQ0/Q72BQ0-deep-research-falcon.md DVU_1584 encodes the alternative sigma factor RpoH (sigma-32), a member of the sigma-70 family mediating transcriptional responses to proteotoxic/heat and related stresses in D. vulgaris |
| GO:0006986 response to unfolded protein | IEA PMID:20437234 Effects of biocides on gene expression in the sulfate-reduci... | NEW | Summary: RpoH regulates expression of molecular chaperones (GroEL, GroES, ClpB, HtpG) and proteases (ClpX) that respond to protein misfolding/unfolding stress. The heat shock response mediated by sigma-32 evolved as a proteotoxic stress response, and D. vulgaris studies show RpoH-dependent chaperone induction under various stress conditions (PMID:20437234). Reason: This annotation captures the fundamental biological purpose of the heat shock response - managing unfolded/misfolded proteins. The RpoH-regulated genes (chaperones, proteases) are protein quality control factors. In D. vulgaris, biocide stress induces the heat shock regulon including groEL, groES, clpX, clpB, htpG - all involved in protein folding and degradation. Supporting Evidence: PMID:20437234 Glut induces expression of genes required to degrade or refold proteins inactivated by either chemical modification or heat shock |
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Download this section (compressed HTML)Q: What is the relationship between RpoH and HrcA in regulating the heat shock response in D. vulgaris? The biocide study shows HrcA up-regulation while RpoH transcript levels remain unchanged.
Q: Is DVU_1584 essential for D. vulgaris survival under heat shock conditions? Are there deletion mutant studies available?
Experiment: ChIP-seq of RpoH in D. vulgaris under heat shock would definitively identify the RpoH regulon members and confirm promoter occupancy, providing direct evidence for sigma factor activity.
Experiment: rpoH deletion mutant phenotyping under heat and oxidative stress would establish essentiality and confirm role in stress survival beyond correlative transcriptomic evidence.
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