RNA polymerase sigma-G factor (also known as SpoIIIG) is the late forespore-specific sigma factor in Bacillus subtilis sporulation. Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released after transcription begins. SigG becomes active only in the forespore compartment approximately 2 hours after sporulation starts, following the earlier action of sigF (the early forespore sigma factor). SigG is responsible for the expression of late sporulation-specific genes in the forespore and auto-stimulates its own transcription. The activity of sigG is tightly regulated during early forespore development by the anti-sigma-G factor Gin (CsfB) and by Lon protease. SigG interacts with Gin via its N-terminal region (residues 1-71), and this interaction inhibits sigG activity until the appropriate developmental stage. The protein contains the characteristic sigma-70 family domains including a helix-turn-helix DNA-binding motif (residues 229-248) and a polymerase core binding motif (residues 67-80).
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000976 transcription cis-regulatory region binding | IBA GO_REF:0000033 | REMOVE | Summary: This annotation suggests sigG binds to transcription cis-regulatory regions. According to the GO definition of sigma factor activity (GO:0016987), sigma factors do not bind DNA on their own but when combined with the core polymerase to form the holoenzyme, they confer promoter specificity. This term is technically inaccurate for sigma factors as they require the core polymerase for DNA binding. Reason: Sigma factors do not bind DNA independently. The GO definition of sigma factor activity explicitly states that "sigma does not bind DNA on its own, when combined with the core to form the holoenzyme, the sigma factor binds specifically to promoter elements." This term implies autonomous DNA binding which is misleading for sigma factors. The correct molecular function is GO:0016987 sigma factor activity. |
| GO:0003899 DNA-directed RNA polymerase activity | IBA GO_REF:0000033 | REMOVE | Summary: This annotation incorrectly attributes catalytic RNA polymerase activity to sigG. Sigma factors are NOT enzymes and do not catalyze the polymerization reaction. The catalytic activity resides in the core polymerase subunits (beta, beta-prime). Reason: This is a clear over-annotation. GO:0003899 is defined as "Catalysis of the reaction: nucleoside triphosphate + RNA(n) = diphosphate + RNA(n+1)." Sigma factors do not possess catalytic activity. The catalytic activity of RNA polymerization is performed by the core enzyme subunits, not by sigma factors. SigG confers promoter specificity but does not catalyze nucleotide addition. UniProt describes sigG as an "initiation factor that promote[s] the attachment of RNA polymerase to specific initiation sites." |
| GO:0006355 regulation of DNA-templated transcription | IBA GO_REF:0000033 | ACCEPT | Summary: SigG regulates transcription by directing RNA polymerase to forespore-specific promoters and by auto-stimulating its own transcription. This is an appropriate biological process annotation for a sigma factor. Reason: Sigma factors inherently regulate transcription by determining which genes are transcribed. SigG specifically regulates the expression of late sporulation genes in the forespore and auto-stimulates its own transcription (per UniProt PMID:18208527). This is a core function of sigG. Supporting Evidence: file:BACSU/sigG/sigG-deep-research-falcon.md See deep research file for comprehensive analysis |
| GO:0016987 sigma factor activity | IBA GO_REF:0000033 | ACCEPT | Summary: This is the primary and most accurate molecular function annotation for sigG. GO:0016987 is defined as the activity of sigma factors that act as promoter specificity subunits of bacterial RNA polymerase. Reason: This is the canonical molecular function for sigG. UniProt explicitly identifies sigG as "RNA polymerase sigma-G factor" belonging to the "sigma-70 factor family." The protein contains all characteristic sigma-70 family domains including the HTH DNA-binding motif (residues 229-248) and polymerase core binding motif (residues 67-80). |
| GO:1903865 sigma factor antagonist complex | IBA GO_REF:0000033 | ACCEPT | Summary: SigG forms a complex with its anti-sigma factor Gin (CsfB). GO:1903865 is defined as "A protein complex which is capable of sigma factor antagonist activity." When sigG is bound by Gin, this complex inhibits sigG transcriptional activity. Reason: UniProt clearly documents that sigG interacts with anti-sigma-G factor Gin (CsfB) via its N-terminal region (residues 1-71). This interaction inhibits sigG activity (per PMID:18208527, PMID:19497328). This sigG-Gin complex represents a sigma factor antagonist complex that prevents premature sigG activity during early forespore development. |
| GO:0003677 DNA binding | IEA GO_REF:0000120 | KEEP AS NON CORE | Summary: This generic DNA binding annotation is inferred from the presence of sigma-70 family domains. While sigG does contain a helix-turn-helix DNA-binding motif (residues 229-248), sigma factors require the core polymerase for DNA binding. Reason: SigG contains a HTH DNA-binding motif at residues 229-248 (UniProt feature). However, per the GO definition of sigma factor activity, "sigma does not bind DNA on its own." The more precise molecular function is GO:0016987 sigma factor activity. This annotation is kept as non-core since it reflects domain architecture but is less informative than the sigma factor activity annotation. |
| GO:0003700 DNA-binding transcription factor activity | IEA GO_REF:0000002 | MODIFY | Summary: This annotation from InterPro domain mapping is incorrect for sigma factors. Sigma factors are not transcription factors in the classical sense; they are subunits of the RNA polymerase holoenzyme that confer promoter specificity. Reason: GO:0003700 is defined as sequence-specific DNA binding that modulates transcription. Sigma factors function differently: they are dissociable subunits of RNA polymerase that determine promoter recognition. The correct term is GO:0016987 sigma factor activity. While both involve promoter recognition, sigma factors act as part of the polymerase holoenzyme rather than as independent transcription factors. Proposed replacements: sigma factor activity |
| GO:0006351 DNA-templated transcription | IEA GO_REF:0000043 | ACCEPT | Summary: SigG is involved in DNA-templated transcription as a component of the RNA polymerase holoenzyme. This is an appropriate general biological process annotation inferred from the UniProt Transcription keyword. Reason: As a sigma factor, sigG is essential for transcription initiation from specific promoters. This general process term appropriately captures sigG's role in transcription. The annotation is supported by UniProt keywords (Transcription) and the well-characterized function of sigma factors in bacterial transcription. |
| GO:0006352 DNA-templated transcription initiation | IEA GO_REF:0000002 | ACCEPT | Summary: This is a highly appropriate annotation for sigma factors. Sigma factors specifically function in transcription initiation by directing RNA polymerase to promoters and are released after initiation. Reason: UniProt states that "Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released." The specific role of sigma factors in initiation (as opposed to elongation or termination) makes this a precise and accurate annotation. |
| GO:0006355 regulation of DNA-templated transcription | IEA GO_REF:0000120 | ACCEPT | Summary: Duplicate annotation (same term as the IBA annotation above) from automated inference. This accurately captures sigG's regulatory role in transcription. Reason: This is a duplicate of the IBA annotation for the same term. Both annotations are valid. Sigma factors regulate transcription by determining which genes are expressed. SigG specifically regulates late forespore gene expression and auto-stimulates its own transcription. |
| GO:0016987 sigma factor activity | IEA GO_REF:0000120 | ACCEPT | Summary: Duplicate annotation (same term as the IBA annotation above) from automated inference based on InterPro domains and UniProt keywords. Reason: This is a duplicate of the IBA annotation for sigma factor activity. Both annotations are valid. This is the core molecular function of sigG, supported by the UniProt Sigma factor keyword and sigma-70 family domain architecture. |
| GO:0030435 sporulation resulting in formation of a cellular spore | IEA GO_REF:0000043 | ACCEPT | Summary: SigG is the late forespore-specific sigma factor essential for sporulation in B. subtilis. This biological process annotation appropriately captures the developmental context of sigG function. Reason: SigG is specifically active in the forespore during sporulation. UniProt states it is "responsible for the expression of sporulation specific genes in the forespore" and is "Active only in the forespore" approximately "2 hours after sporulation starts." The Sporulation UniProt keyword correctly maps to this GO term. |
| GO:2000142 regulation of DNA-templated transcription initiation | IEA GO_REF:0000108 | ACCEPT | Summary: This annotation is logically inferred from sigma factor activity (GO:0016987). Since sigma factors specifically function at the initiation step, regulation of transcription initiation is an appropriate process annotation. Reason: This is a more specific version of the transcription regulation annotation that correctly reflects that sigma factors act at the initiation stage. Since sigma factors "promote the attachment of RNA polymerase to specific initiation sites," they specifically regulate the initiation step of transcription. This logical inference from GO:0016987 is valid. |
| GO:0045152 antisigma factor binding | IC PMID:18208527 How the early sporulation sigma factor sigmaF delays the swi... | NEW | Summary: SigG binds to its anti-sigma factor Gin (CsfB) via residues 1-71. This interaction is critical for temporal regulation of sigG activity during sporulation. Reason: UniProt documents direct interaction between sigG and anti-sigma-G factor Gin (PMID:18208527, PMID:19497328). The N-terminal region (residues 1-71) is annotated as the recognition region for Gin binding. This molecular function annotation would accurately capture sigG's ability to bind its cognate anti-sigma factor. Supporting Evidence: PMID:18208527 Gin interacts strongly with sigma(G) but not with sigma(F) in a yeast two-hybrid experiment PMID:19497328 The Gin protein, encoded by csfB, is able to strongly inhibit the activity of one of these factors, sigma(G), in vivo |
| GO:0042601 endospore-forming forespore | IC PMID:18208527 How the early sporulation sigma factor sigmaF delays the swi... | NEW | Summary: SigG is specifically localized and active in the forespore compartment during sporulation. This cellular component annotation would capture the spatial specificity of sigG function. Reason: UniProt clearly states that sigG is "Active only in the forespore" (PMID:18208527). The forespore is the compartment that will ultimately become the mature spore. This cellular component annotation would accurately capture the subcellular localization and activity context of sigG. Supporting Evidence: PMID:18208527 Sporulation in Bacillus subtilis is a primitive differentiation process involving two cell types, the forespore and the mother cell |
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Download this section (compressed HTML)Q: What is the complete set of genes whose expression is directly controlled by sigG in the forespore, and how does this differ from sigF-controlled genes?
Q: What is the mechanism by which Lon protease contributes to sigG regulation, and does it act on sigG directly or on Gin?
Experiment: ChIP-seq analysis of sigG binding sites to define the complete sigG regulon in sporulating B. subtilis cells. This would provide a comprehensive view of direct sigG target genes and validate the biological process annotations.
Experiment: Time-course transcriptomics comparing wild-type and sigG mutant strains during sporulation to identify sigG-dependent gene expression changes. This would help distinguish direct from indirect effects of sigG on sporulation gene expression.
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