SigF (also known as SpoIIAC) encodes the RNA polymerase sigma-F factor, a member of the sigma-70 family of alternative sigma factors that is specifically activated in the forespore compartment during Bacillus subtilis sporulation. SigF is the first compartment-specific transcription factor activated after asymmetric septation, initiating the early forespore transcriptional program. The protein contains conserved sigma-70 regions (2, 3, and 4) including a helix-turn-helix DNA-binding motif that recognizes specific promoter sequences. SigF activity is tightly controlled by an elegant partner-switching mechanism involving the anti-sigma factor SpoIIAB (which binds and sequesters SigF) and the anti-anti-sigma factor SpoIIAA. Before septation, SpoIIAB keeps SigF inactive by direct binding and also phosphorylates SpoIIAA to prevent its antagonistic activity. Upon asymmetric septation, the membrane-associated phosphatase SpoIIE preferentially dephosphorylates SpoIIAA-P in the forespore, allowing unphosphorylated SpoIIAA to bind SpoIIAB and release SigF for holoenzyme formation. This partner-switching mechanism ensures compartment-specific activation of SigF exclusively in the forespore despite the protein being present in both compartments. SigF directs transcription of early forespore genes including sigG (the late forespore sigma factor), csfB (an anti-sigma factor that reinforces cell-type specificity), and the forespore-specific promoter of rho (transcription termination factor). SigF also autoregulates the spoIIA operon from which it is expressed. The sequential activation of sigma factors (SigF in forespore, SigE in mother cell, followed by SigG and SigK) orchestrates the complex developmental program of sporulation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
|
GO:0000976
transcription cis-regulatory region binding
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: Sigma factors bind to specific promoter sequences to position RNA polymerase for transcription initiation. SigF recognizes and binds to SigF-dependent promoter elements consisting of a -10 region (consensus similar to GGTAAAAATA) and a -35 region (GAATA) separated by an A/T-rich spacer. This has been demonstrated through mutational analysis of the forespore-specific rho promoter where mutations in the -35 GAATA element abolished forespore-specific transcription (Bidnenko et al. 2024). The helix-turn-helix motif in SigF (residues 221-240 per UniProt) mediates DNA binding.
Reason: The IBA annotation for transcription cis-regulatory region binding is well-supported by the molecular function of sigma factors. SigF contains a characterized helix-turn-helix DNA-binding motif and has demonstrated sequence-specific recognition of promoter elements. The 2024 work on the rho promoter provides direct evidence that SigF recognizes specific DNA sequences at its target promoters.
Supporting Evidence:
file:BACSU/sigF/sigF-deep-research-falcon.md
a SigF-like -10 (GGTAAAAATA) and GAATA -35 separated by an A/T-rich spacer were identified; mutation of the -35 GAATA element abolished the forespore GFP burst and reduced luciferase activity
UniProt:P07860
InterPro; IPR001387; Cro/C1-type_HTH
|
|
GO:0003899
DNA-directed RNA polymerase activity
|
IBA
GO_REF:0000033 |
REMOVE |
Summary: This annotation suggests SigF has RNA polymerase catalytic activity, which is inaccurate. Sigma factors do not possess intrinsic polymerase activity - they are initiation factors that confer promoter specificity to the RNA polymerase core enzyme. The catalytic activity resides in the core RNAP subunits (alpha, beta, beta-prime), not in sigma factors.
Reason: Sigma factors including SigF do not catalyze RNA synthesis. They function as specificity factors that direct the RNA polymerase holoenzyme to specific promoters. The RNAP core enzyme provides the catalytic activity. This annotation conflates the function of the sigma subunit with the catalytic core. The correct annotation is sigma factor activity (GO:0016987), which is already present.
Supporting Evidence:
UniProt:P07860
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
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: SigF regulates transcription by conferring promoter specificity to RNA polymerase, thereby activating a specific set of forespore genes during sporulation. SigF directs expression of numerous sporulation-specific genes including sigG, csfB, and the forespore promoter of rho. SigF also autoregulates the spoIIA operon.
Reason: As an alternative sigma factor, SigF fundamentally regulates transcription by determining which promoters the RNAP holoenzyme can recognize. SigF-dependent transcription activates the early forespore program. This is a core function of sigma factors and is well-documented for SigF.
Supporting Evidence:
UniProt:P07860
This sigma factor is responsible for the expression of sporulation specific genes
|
|
GO:0016987
sigma factor activity
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: SigF is a well-characterized sigma factor of the sigma-70 family. It contains conserved sigma-70 regions (regions 2, 3, and 4) that mediate core RNAP binding and promoter recognition. Biochemical and genetic studies have definitively established SigF as a sigma factor that associates with RNAP core and directs transcription initiation at SigF-dependent promoters.
Reason: This is the primary molecular function of SigF. The sigma factor activity annotation accurately captures SigF's role in conferring promoter specificity to RNA polymerase. This is supported by extensive biochemical characterization, domain analysis, and genetic studies demonstrating SigF-dependent transcription.
Supporting Evidence:
UniProt:P07860
Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released
UniProt:P07860
Associates with the RNAP core only in stationary phase cells
|
|
GO:1903865
sigma factor antagonist complex
|
IBA
GO_REF:0000033 |
ACCEPT |
Summary: SigF forms a complex with its anti-sigma factor SpoIIAB, which inhibits SigF activity by direct binding. The SigF-SpoIIAB complex represents a sigma factor antagonist complex where SpoIIAB sequesters SigF and prevents holoenzyme formation. This complex is a central component of the partner-switching mechanism that controls SigF activation.
Reason: The formation of a SigF-SpoIIAB inhibitory complex is well-documented and represents a key regulatory mechanism. SpoIIAB binds SigF through contacts at conserved sigma-70 regions 2.1, 3.1, and 4.1. This complex formation is essential for keeping SigF inactive in the pre-divisional cell and in the mother cell compartment after septation.
Supporting Evidence:
UniProt:P07860
Interaction with SpoIIAB inhibits sigma-F activity throughout the cell before the formation of the asymmetric septum
|
|
GO:0003677
DNA binding
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: SigF binds DNA as part of the RNAP holoenzyme to recognize promoter sequences. SigF contains a characterized helix-turn-helix DNA-binding motif (residues 221-240) that mediates sequence-specific recognition of SigF-dependent promoters.
Reason: While this IEA annotation is more general than the IBA annotation for transcription cis-regulatory region binding (GO:0000976), it is not incorrect. Sigma factors do bind DNA as part of the holoenzyme. The presence of a characterized HTH motif in SigF supports this annotation. This can be retained as a broader annotation alongside the more specific term.
Supporting Evidence:
UniProt:P07860
InterPro; IPR001387; Cro/C1-type_HTH
|
|
GO:0003700
DNA-binding transcription factor activity
|
IEA
GO_REF:0000002 |
MODIFY |
Summary: This term is intended for sequence-specific DNA-binding transcription factors that regulate transcription by binding to cis-regulatory elements. While sigma factors do bind DNA and regulate transcription, they function mechanistically differently from classical transcription factors - sigma factors confer promoter recognition to the RNA polymerase core rather than acting as independent regulatory factors.
Reason: The term GO:0003700 is designed for classical transcription factors that independently bind DNA regulatory elements. Sigma factors have a distinct mechanism - they are subunits of the RNAP holoenzyme that confer promoter specificity. The more appropriate and specific term is GO:0016987 (sigma factor activity), which is already annotated. This IEA annotation from InterPro mapping may be overly broad.
Proposed replacements:
sigma factor activity
Supporting Evidence:
UniProt:P07860
Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released
|
|
GO:0006351
DNA-templated transcription
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: SigF participates in DNA-templated transcription as the sigma subunit of the RNA polymerase holoenzyme. As a sigma factor, it enables transcription initiation at SigF-dependent promoters during sporulation.
Reason: This biological process annotation correctly captures SigF's involvement in transcription. As a sigma factor, SigF is directly involved in the transcription process by conferring promoter specificity to RNAP and enabling transcription initiation.
Supporting Evidence:
UniProt:P07860
Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites
UniProt:P07860
This sigma factor is responsible for the expression of sporulation specific genes
|
|
GO:0006352
DNA-templated transcription initiation
|
IEA
GO_REF:0000002 |
ACCEPT |
Summary: SigF is specifically involved in transcription initiation - sigma factors function at the initiation step to position RNA polymerase at promoters and enable formation of the open complex. After initiation, sigma factors are typically released from the elongating polymerase.
Reason: This annotation is highly appropriate for SigF. Sigma factors function specifically at the transcription initiation step - they enable promoter recognition and open complex formation but are released during the transition to elongation. This term accurately captures the specific stage of transcription where sigma factors act.
Supporting Evidence:
UniProt:P07860
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: Duplicate annotation with the IBA entry. SigF regulates transcription by determining which promoters are recognized by the RNAP holoenzyme, thereby activating transcription of forespore-specific genes.
Reason: This is a valid annotation for SigF regardless of evidence code. As an alternative sigma factor, SigF regulates transcription by conferring promoter specificity. The duplicate with different evidence codes is acceptable and reflects independent inference paths reaching the same conclusion.
Supporting Evidence:
UniProt:P07860
This sigma factor is responsible for the expression of sporulation specific genes
|
|
GO:0016987
sigma factor activity
|
IEA
GO_REF:0000120 |
ACCEPT |
Summary: Duplicate annotation with the IBA entry. SigF is a well-characterized member of the sigma-70 family with demonstrated sigma factor activity.
Reason: This core molecular function annotation is appropriate for SigF. The duplicate with IEA evidence code reflects independent computational inference confirming the phylogenetically-derived IBA annotation. Duplicates with different evidence types are acceptable in GO annotation.
Supporting Evidence:
UniProt:P07860
Belongs to the sigma-70 factor family
|
|
GO:0030435
sporulation resulting in formation of a cellular spore
|
IEA
GO_REF:0000043 |
ACCEPT |
Summary: SigF plays an essential role in sporulation. It is the first compartment-specific sigma factor activated during sporulation and initiates the early forespore transcriptional program. Mutations in sigF block sporulation and prevent formation of mature spores.
Reason: This biological process annotation appropriately captures SigF's essential role in sporulation. SigF is absolutely required for spore formation - mutations abolish spore production and induction of sporulation-associated enzymes. SigF initiates the forespore developmental program that ultimately leads to spore formation.
Supporting Evidence:
UniProt:P07860
In spo-63 (loss of residues 27-255); no spores develop, no induction of sporulation-associated enzymes
|
|
GO:2000142
regulation of DNA-templated transcription initiation
|
IEA
GO_REF:0000108 |
ACCEPT |
Summary: SigF specifically regulates transcription at the initiation step. As a sigma factor, it enables recognition of specific promoters and formation of the initiation complex. This term is more specific than the general regulation of transcription term and accurately reflects sigma factor function.
Reason: This annotation correctly captures that sigma factors regulate transcription specifically at the initiation step. SigF enables RNAP to recognize and initiate transcription from SigF-dependent promoters. This is a precise characterization of sigma factor function.
Supporting Evidence:
UniProt:P07860
Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites
|
Q: What is the complete SigF regulon and how does it compare across Bacillus species?
Q: How is the partner-switching mechanism quantitatively tuned to ensure reliable compartment-specific activation?
Experiment: ChIP-seq analysis of SigF binding during sporulation would enable genome-wide identification of SigF binding sites, comprehensively defining the SigF regulon and revealing any previously uncharacterized target promoters.
Hypothesis: SigF binds to specific promoter sequences genome-wide to activate a defined early forespore transcriptional program
Type: ChIP-seq
Experiment: Quantitative analysis of SpoIIE phosphatase activity in forespore vs mother cell would illuminate the molecular basis of compartment-specific SigF activation by understanding how SpoIIE activity is restricted to the forespore.
Hypothesis: SpoIIE phosphatase activity is higher in the forespore compartment due to its localization at the asymmetric septum
Type: Biochemical assay
Exported on March 22, 2026 at 02:43 AM
Organism: Bacillus subtilis
Sequence:
MDVEVKKNGKNAQLKDHEVKELIKQSQNGDQQARDLLIEKNMRLVWSVVQRFLNRGYEPDDLFQIGCIGLLKSVDKFDLTYDVRFSTYAVPMIIGEIQRFIRDDGTVKVSRSLKELGNKIRRAKDELSKTLGRVPTVQEIADHLEIEAEDVVLAQEAVRAPSSIHETVYENDGDPITLLDQIADNSEEKWFDKIALKEAISDLEEREKLIVYLRYYKDQTQSEVAERLGISQVQVSRLEKKILKQIKVQMDHTDG
I begin with the InterPro architecture, which is diagnostic for a σ70-family initiation factor. The core scaffold is defined by IPR000943 (RNA polymerase sigma-70, residues 17–252) and reinforced by IPR014284 (RNA polymerase sigma-70-like domain, residues 33–250), together with IPR050239 (Sigma-70 factor family, RNA polymerase initiation factors, residues 12–247). The presence of multiple σ-B/F/G and σ-F-type family signatures—IPR014236 (RNA polymerase sigma-F type, residues 22–249) and IPR014322 (RNA polymerase sigma-B/F/G type, residues 30–250)—pinpoints a sporulation-associated subgroup that redirects transcription during developmental transitions in Firmicutes. The ordered segmentation into canonical σ70 submodules is explicit: IPR013325 and IPR007627 (RNA polymerase sigma-70 region 2, residues 13–105 and 37–104) establish the promoter-melting and -10 element recognition module; IPR007624 (region 3, residues 115–187) and IPR007630 (region 4, residues 199–247) build the promoter-upstream element recognition and RNAP-binding interface; and IPR036388 (Winged helix-like DNA-binding domain superfamily, residues 105–253) plus IPR013324 (region 3/4-like superfamily, residues 109–250) define the DNA-binding core that coordinates with the polymerase. The C-terminal IPR001387 (Cro/C1-type helix-turn-helix, residues 220–240) supplies a helix-turn-helix element that stabilizes DNA and RNAP contacts. Together, this contiguous σ70 module suite causes high-affinity, sequence-specific promoter engagement and controlled handoff to the core enzyme—an architecture that encodes sigma factor activity.
From this domain logic, the molecular function resolves as sigma factor activity: the combined region 2/3/4 architecture and winged-helix module confer sequence-specific promoter recognition and initiation control, consistent with GO:0016987 sigma factor activity. The σ-B/F/G signature indicates specialization for sporulation regulons in Bacillus; this specialization channels transcription initiation toward developmental gene sets, thus driving the biological process of sporulation. Consequently, the process-level role encompasses transcription initiation and its deployment in development; the most specific, causally supported biological process here is sporulation resulting from developmental regulation (GO:0030435 sporulation), while transcription initiation (GO:0006352) captures the mechanistic step that this factor executes.
Cellular placement follows from function and architecture. Sigma factors are soluble transcription initiation factors that operate with the bacterial RNA polymerase within the cytoplasmic nucleoid territory. The absence of transmembrane or secretion signals and the soluble σ70 fold argue for a cytoplasmic location, aligning with GO:0005737 cytoplasm.
Mechanistically, region 2 recognizes and melts promoter -10 elements, region 3 senses upstream elements and stabilizes the open complex, and region 4—with its helix-turn-helix—positions the factor on upstream DNA and docks to RNAP’s β and β′ surfaces. This coordinated assembly selects and activates sporulation promoters, switching the transcriptional program toward developmental pathways. Likely interaction partners include the core RNA polymerase and nucleoid-associated proteins that sculpt sporulation promoters. I hypothesize transient complexes with RNAP (β/β′/β″ assemblies) and possible contacts with sporulation-stage nucleoid proteins that modulate DNA topology and promoter accessibility, enabling efficient initiation at sporulation gene loci.
A cytoplasmic initiation factor that redirects bacterial transcription toward sporulation programs. It binds bacterial RNA polymerase and engages promoter DNA via a modular sigma-70 fold, using distinct recognition and melting elements to assemble open complexes at sporulation promoters. By selecting and activating the appropriate initiation sites, it drives developmental transcription required for the formation and maturation of spores.
Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released.
IPR050239, family) — residues 12-247IPR013325, homologous_superfamily) — residues 13-105IPR000943, domain) — residues 17-252IPR014236, family) — residues 22-249IPR014322, family) — residues 30-250IPR014284, domain) — residues 33-250IPR007627, domain) — residues 37-104IPR036388, homologous_superfamily) — residues 105-253IPR013324, homologous_superfamily) — residues 109-250IPR007624, domain) — residues 115-187IPR007630, domain) — residues 199-247IPR001387, domain) — residues 220-240Molecular Function: molecular_function (GO:0003674), binding (GO:0005488), protein binding (GO:0005515)
Biological Process: biological_process (GO:0008150), cellular process (GO:0009987), biological regulation (GO:0065007), response to stimulus (GO:0050896), regulation of biological process (GO:0050789), cellular response to stimulus (GO:0051716), response to stress (GO:0006950), regulation of metabolic process (GO:0019222), regulation of cellular process (GO:0050794), regulation of macromolecule metabolic process (GO:0060255), regulation of cellular metabolic process (GO:0031323), regulation of primary metabolic process (GO:0080090), cellular response to stress (GO:0033554), regulation of biosynthetic process (GO:0009889), regulation of nitrogen compound metabolic process (GO:0051171), regulation of nucleobase-containing compound metabolic process (GO:0019219), regulation of RNA metabolic process (GO:0051252), regulation of macromolecule biosynthetic process (GO:0010556), regulation of gene expression (GO:0010468), regulation of DNA-templated transcription in response to stress (GO:0043620), regulation of cellular biosynthetic process (GO:0031326), regulation of RNA biosynthetic process (GO:2001141), regulation of DNA-templated transcription (GO:0006355), regulation of nucleic acid-templated transcription (GO:1903506)
Cellular Component: cellular_component (GO:0005575), cellular anatomical entity (GO:0110165), protein-containing complex (GO:0032991), cell periphery (GO:0071944), membrane (GO:0016020), external encapsulating structure (GO:0030312), cell wall (GO:0005618), plasma membrane (GO:0005886), spore wall (GO:0031160)
Generated by BioReason
Exported on March 22, 2026 at 02:43 AM
Organism: Bacillus subtilis
Sequence:
MDVEVKKNGKNAQLKDHEVKELIKQSQNGDQQARDLLIEKNMRLVWSVVQRFLNRGYEPDDLFQIGCIGLLKSVDKFDLTYDVRFSTYAVPMIIGEIQRFIRDDGTVKVSRSLKELGNKIRRAKDELSKTLGRVPTVQEIADHLEIEAEDVVLAQEAVRAPSSIHETVYENDGDPITLLDQIADNSEEKWFDKIALKEAISDLEEREKLIVYLRYYKDQTQSEVAERLGISQVQVSRLEKKILKQIKVQMDHTDG
I begin with the InterPro architecture, which is diagnostic for a σ70-family initiation factor. The core scaffold is defined by IPR000943 (RNA polymerase sigma-70, residues 17–252) and reinforced by IPR014284 (RNA polymerase sigma-70-like domain, residues 33–250), together with IPR050239 (Sigma-70 factor family, RNA polymerase initiation factors, residues 12–247). The presence of multiple σ-B/F/G and σ-F-type family signatures—IPR014236 (RNA polymerase sigma-F type, residues 22–249) and IPR014322 (RNA polymerase sigma-B/F/G type, residues 30–250)—pinpoints a sporulation-associated subgroup that redirects transcription during developmental transitions in Firmicutes. The ordered segmentation into canonical σ70 submodules is explicit: IPR013325 and IPR007627 (RNA polymerase sigma-70 region 2, residues 13–105 and 37–104) establish the promoter-melting and -10 element recognition module; IPR007624 (region 3, residues 115–187) and IPR007630 (region 4, residues 199–247) build the promoter-upstream element recognition and RNAP-binding interface; and IPR036388 (Winged helix-like DNA-binding domain superfamily, residues 105–253) plus IPR013324 (region 3/4-like superfamily, residues 109–250) define the DNA-binding core that coordinates with the polymerase. The C-terminal IPR001387 (Cro/C1-type helix-turn-helix, residues 220–240) supplies a helix-turn-helix element that stabilizes DNA and RNAP contacts. Together, this contiguous σ70 module suite causes high-affinity, sequence-specific promoter engagement and controlled handoff to the core enzyme—an architecture that encodes sigma factor activity.
From this domain logic, the molecular function resolves as sigma factor activity: the combined region 2/3/4 architecture and winged-helix module confer sequence-specific promoter recognition and initiation control, consistent with GO:0016987 sigma factor activity. The σ-B/F/G signature indicates specialization for sporulation regulons in Bacillus; this specialization channels transcription initiation toward developmental gene sets, thus driving the biological process of sporulation. Consequently, the process-level role encompasses transcription initiation and its deployment in development; the most specific, causally supported biological process here is sporulation resulting from developmental regulation (GO:0030435 sporulation), while transcription initiation (GO:0006352) captures the mechanistic step that this factor executes.
Cellular placement follows from function and architecture. Sigma factors are soluble transcription initiation factors that operate with the bacterial RNA polymerase within the cytoplasmic nucleoid territory. The absence of transmembrane or secretion signals and the soluble σ70 fold argue for a cytoplasmic location, aligning with GO:0005737 cytoplasm.
Mechanistically, region 2 recognizes and melts promoter -10 elements, region 3 senses upstream elements and stabilizes the open complex, and region 4—with its helix-turn-helix—positions the factor on upstream DNA and docks to RNAP’s β and β′ surfaces. This coordinated assembly selects and activates sporulation promoters, switching the transcriptional program toward developmental pathways. Likely interaction partners include the core RNA polymerase and nucleoid-associated proteins that sculpt sporulation promoters. I hypothesize transient complexes with RNAP (β/β′/β″ assemblies) and possible contacts with sporulation-stage nucleoid proteins that modulate DNA topology and promoter accessibility, enabling efficient initiation at sporulation gene loci.
A cytoplasmic initiation factor that redirects bacterial transcription toward sporulation programs. It binds bacterial RNA polymerase and engages promoter DNA via a modular sigma-70 fold, using distinct recognition and melting elements to assemble open complexes at sporulation promoters. By selecting and activating the appropriate initiation sites, it drives developmental transcription required for the formation and maturation of spores.
Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released.
IPR050239, family) — residues 12-247IPR013325, homologous_superfamily) — residues 13-105IPR000943, domain) — residues 17-252IPR014236, family) — residues 22-249IPR014322, family) — residues 30-250IPR014284, domain) — residues 33-250IPR007627, domain) — residues 37-104IPR036388, homologous_superfamily) — residues 105-253IPR013324, homologous_superfamily) — residues 109-250IPR007624, domain) — residues 115-187IPR007630, domain) — residues 199-247IPR001387, domain) — residues 220-240Molecular Function: molecular_function (GO:0003674), binding (GO:0005488), protein binding (GO:0005515)
Biological Process: biological_process (GO:0008150), cellular process (GO:0009987), biological regulation (GO:0065007), response to stimulus (GO:0050896), regulation of biological process (GO:0050789), cellular response to stimulus (GO:0051716), response to stress (GO:0006950), regulation of metabolic process (GO:0019222), regulation of cellular process (GO:0050794), regulation of macromolecule metabolic process (GO:0060255), regulation of cellular metabolic process (GO:0031323), regulation of primary metabolic process (GO:0080090), cellular response to stress (GO:0033554), regulation of biosynthetic process (GO:0009889), regulation of nitrogen compound metabolic process (GO:0051171), regulation of nucleobase-containing compound metabolic process (GO:0019219), regulation of RNA metabolic process (GO:0051252), regulation of macromolecule biosynthetic process (GO:0010556), regulation of gene expression (GO:0010468), regulation of DNA-templated transcription in response to stress (GO:0043620), regulation of cellular biosynthetic process (GO:0031326), regulation of RNA biosynthetic process (GO:2001141), regulation of DNA-templated transcription (GO:0006355), regulation of nucleic acid-templated transcription (GO:1903506)
Cellular Component: cellular_component (GO:0005575), cellular anatomical entity (GO:0110165), protein-containing complex (GO:0032991), cell periphery (GO:0071944), membrane (GO:0016020), external encapsulating structure (GO:0030312), cell wall (GO:0005618), plasma membrane (GO:0005886), spore wall (GO:0031160)
Generated by BioReason
provider: falcon
model: Edison Scientific Literature
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start_time: '2025-12-17T23:25:06.542428'
end_time: '2025-12-17T23:35:51.411009'
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template_file: templates/gene_research_go_focused.md
template_variables:
organism: BACSU
gene_id: sigF
gene_symbol: sigF
uniprot_accession: P07860
protein_description: 'RecName: Full=RNA polymerase sigma-F factor; AltName: Full=Sporulation
sigma factor; AltName: Full=Stage II sporulation protein AC;'
gene_info: Name=sigF; Synonyms=spoIIAC; OrderedLocusNames=BSU23450;
organism_full: Bacillus subtilis (strain 168).
protein_family: Belongs to the sigma-70 factor family. .
protein_domains: Cro/C1-type_HTH. (IPR001387); RNA_pol_sigma-70_dom. (IPR014284);
RNA_pol_sigma-B/F/G. (IPR014322); RNA_pol_sigma-F. (IPR014236); RNA_pol_sigma70.
(IPR000943)
provider_config:
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citation_count: 28
BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.
DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'sigF' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information
Please provide a comprehensive research report on the gene sigF (gene ID: sigF, UniProt: P07860) in BACSU.
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
Question: You are an expert researcher providing comprehensive, well-cited information.
Provide detailed information focusing on:
1. Key concepts and definitions with current understanding
2. Recent developments and latest research (prioritize 2023-2024 sources)
3. Current applications and real-world implementations
4. Expert opinions and analysis from authoritative sources
5. Relevant statistics and data from recent studies
Format as a comprehensive research report with proper citations. Include URLs and publication dates where available.
Always prioritize recent, authoritative sources and provide specific citations for all major claims.
BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.
DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'sigF' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information
Please provide a comprehensive research report on the gene sigF (gene ID: sigF, UniProt: P07860) in BACSU.
The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
Plan
Objective 1: Verify identity of the target protein and avoid symbol ambiguity. Completed: spoIIAC (sigF) encodes the sporulation sigma factor σF in Bacillus subtilis; σF is a σ70-family alternative sigma factor with conserved σ70 regions and forespore-restricted activity during sporulation (haldenwang1995thesigmafactors pages 17-18, lewis1996compartmentalizeddistributionof pages 6-8, serrano2015dualspecificityantisigmafactor pages 2-4).
Objective 2: Assemble recent (2023–2024) literature and core primary sources. Completed: 2024 JBC and MMBR reviews provide new, compartment-specific σF-linked regulation and DNA-repair integration during sporulation; foundational mechanistic studies (1993–1999) define SpoIIAB/SpoIIAA/SpoIIE control of σF (bidnenko2024complexsporulationspecificexpression pages 11-12, bidnenko2024complexsporulationspecificexpression pages 3-4, bidnenko2024complexsporulationspecificexpression pages 4-6, bidnenko2024complexsporulationspecificexpression pages 6-7, bidnenko2024complexsporulationspecificexpression pages 10-11, pedrazareyes2024bacillussubtilisstressassociated pages 18-20, haldenwang1995thesigmafactors pages 17-18, lewis1996compartmentalizeddistributionof pages 6-8, serrano2015dualspecificityantisigmafactor pages 19-20, serrano2015dualspecificityantisigmafactor pages 2-4, serrano2015dualspecificityantisigmafactor pages 6-7).
Objective 3–8: Extract key mechanisms, recent advances, applications, expert perspectives, quantitative data, and produce a concise artifact; then write the report with citations. Completed below.
Comprehensive research report: Bacillus subtilis sigF (spoIIAC) – σF, the forespore-specific sigma factor
1) Key concepts and definitions
- Identity and family: sigF (spoIIAC) encodes σF, an alternative RNA polymerase sigma factor that launches the early forespore transcriptional program in Bacillus subtilis. Sequence analyses and functional genetics established spoIIAC as a bona fide sigma factor within the σ70 family; σF contains conserved σ70 regions (e.g., regions 2/3/4) that mediate core binding and promoter recognition (haldenwang1995thesigmafactors pages 17-18, serrano2015dualspecificityantisigmafactor pages 2-4).
- Core regulatory module and partner switching: σF is held inactive by the anti-sigma factor SpoIIAB, which binds σF and prevents holoenzyme formation; SpoIIAB also functions as a serine kinase that phosphorylates the anti–anti-sigma SpoIIAA. Dephosphorylated SpoIIAA binds SpoIIAB, liberating σF. The PP2C-like phosphatase SpoIIE dephosphorylates SpoIIAA-P at the sporulation septum, triggering σF activation specifically in the forespore (haldenwang1995thesigmafactors pages 17-18, lewis1996compartmentalizeddistributionof pages 6-8). Classic biochemical and genetic analyses established SpoIIAB–σF binding and mapped SpoIIAB contact sites on σF to three conserved σ70 regions (2.1, 3.1, 4.1), reinforcing the σ70-family placement (haldenwang1995thesigmafactors pages 17-18, lewis1996compartmentalizeddistributionof pages 6-8).
- Compartment and timing of activity: σF protein accumulates around ~1 h after sporulation onset and is activated specifically in the forespore compartment following asymmetric septation; σF-dependent transcription is prespore-restricted even though σF protein can be detected in both compartments, indicating that activation—not localization—controls compartment specificity (lewis1996compartmentalizeddistributionof pages 6-8). Septation-dependent SpoIIE action at the septum underlies this compartmental switch (lewis1996compartmentalizeddistributionof pages 6-8).
- Genetic organization: sigF resides as the third cistron in the tricistronic spoIIA operon (spoIIAA–spoIIAB–spoIIAC/sigF), which couples synthesis of the anti–anti-, anti-, and sigma factor in one unit; σF also autoregulates the spoIIA operon via an upstream promoter (haldenwang1995thesigmafactors pages 17-18).
2) Recent developments and latest research (emphasis 2023–2024)
- 2024: Compartment-specific σF control of transcription termination factor Rho. A JBC study demonstrated that rho expression is reprogrammed during sporulation through dual, compartment-specific mechanisms: read-through transcription from a distal SigH- and Spo0A~P-regulated promoter drives mother-cell expression, while a genuine SigF-dependent promoter in the rho 5′ UTR drives forespore expression. A SigF-like −10 (GGTAAAAATA) and GAATA −35 separated by an A/T-rich spacer were identified; mutation of the −35 GAATA element abolished the forespore GFP burst and reduced luciferase activity, phenocopying ΔsigF. ΔsigF significantly diminishes forespore-specific rho expression, whereas ΔsigE does not, showing forespore-specific σF control. These sporulation-specific promoters compensate for silencing of the vegetative SigA-dependent rho promoter, enabling “refueling” of Rho protein in both compartments; altering this pattern impacts spore morphology and revival efficiency (JBC, 2024-12; https://doi.org/10.1016/j.jbc.2024.107905) (bidnenko2024complexsporulationspecificexpression pages 4-6, bidnenko2024complexsporulationspecificexpression pages 6-7, bidnenko2024complexsporulationspecificexpression pages 10-11, bidnenko2024complexsporulationspecificexpression pages 3-4, bidnenko2024complexsporulationspecificexpression pages 1-2).
- 2024: Integration with DNA repair and stress-associated mutagenesis. An MMBR review synthesized recent findings that several DNA repair and maintenance factors are expressed in a compartment-specific manner during sporulation, with σF directing forespore expression of certain functions (e.g., YwjD UV endonuclease). The review details lesion-specific processing cascades in sporulating cells and shows that many repair proteins (including σF-driven or forespore-enriched proteins) are packaged in spores and become active upon germination, linking σF-dependent transcription to spore quality and resilience (MMBR, 2024-06; https://doi.org/10.1128/mmbr.00158-23) (pedrazareyes2024bacillussubtilisstressassociated pages 18-20).
- Refined understanding of σF discrimination by CsfB (contextual modern mechanistic work): CsfB (Gin), a dual-specificity anti-sigma, reinforces cell-type specificity by binding σG and σE but discriminating against σF and σK via specific residues in conserved σ70 region 2.1/2.3, respectively (E39 in σF vs N45 in σG; N100 in σE vs E93 in σK). This prevents ectopic σG activity in pre-divisional cells and helps the σE→σK transition; spore formation efficiency changes and surface-layer composition differences illustrate phenotypic outcomes (PLOS Genetics, 2015-04; https://doi.org/10.1371/journal.pgen.1005104) (serrano2015dualspecificityantisigmafactor pages 19-20, serrano2015dualspecificityantisigmafactor pages 2-4, serrano2015dualspecificityantisigmafactor pages 6-7).
3) Current applications and real-world implementations
- Live-cell and compartment-specific reporters controlled by σF. The Prho-gfp and Prho-luc fusions constructed at the native rho locus provide real-time, compartment-resolved readouts of forespore σF activity in vivo; mutational analyses of the SigF-dependent −35 element serve both as validation and as practical tools for dissecting forespore transcription circuits (bidnenko2024complexsporulationspecificexpression pages 6-7, bidnenko2024complexsporulationspecificexpression pages 12-13, bidnenko2024complexsporulationspecificexpression pages 1-2).
- Forespore DNA repair engineering and spore quality: The 2024 MMBR synthesis highlights σF-controlled expression of forespore DNA repair enzymes (e.g., YwjD endonuclease) that contribute to UV damage processing and spore fitness. These insights guide strategies to optimize spore robustness for industrial or probiotic applications by tuning σF-driven repair pathway expression during sporulation (pedrazareyes2024bacillussubtilisstressassociated pages 18-20).
- Regulatory circuit design principles: The σF/SpoIIAB/SpoIIAA/SpoIIE module exemplifies a partner-switching, phosphorylation-controlled, septation-gated signal transduction circuit. It inspires synthetic compartmentalized gene-expression designs and time-locked differentiation programs in Gram-positive bacteria where asymmetric division and σF-like modules exist (haldenwang1995thesigmafactors pages 17-18, lewis1996compartmentalizeddistributionof pages 6-8, bidnenko2024complexsporulationspecificexpression pages 4-6, bidnenko2024complexsporulationspecificexpression pages 6-7).
4) Expert opinions and authoritative analyses
- Reviews defining σF and its control: The Microbiological Reviews article by Haldenwang remains a cornerstone that cataloged B. subtilis sigma factors, mapped spoIIAC as σF, described σF autoregulation, and established the logic of anti-sigma and anti–anti-sigma control (Microbiol. Rev., 1995-03; https://doi.org/10.1128/mr.59.1.1-30.1995) (haldenwang1995thesigmafactors pages 17-18). The 1996–1999 primary literature from Losick, Errington and colleagues elucidated compartmental activation by SpoIIE at the septum and the prespore-restricted transcriptional output of σF (Genes Dev., 1999-05; https://doi.org/10.1101/gad.13.9.1156) (lewis1996compartmentalizeddistributionof pages 6-8).
- 2024 authoritative perspective: Bidnenko et al. conclude that compartment-specific rerouting of rho expression—SigH/Spo0A~P-dependent read-through in the mother cell and direct SigF-dependent forespore transcription—is essential for generating spores with normal morphology and revival kinetics, and that σF-dependent “refueling” of Rho during morphogenesis primarily determines outgrowth quality (JBC, 2024-12; https://doi.org/10.1016/j.jbc.2024.107905) (bidnenko2024complexsporulationspecificexpression pages 10-11).
5) Relevant statistics and data from recent and primary studies
- Timing and compartment: σF protein often becomes detectable ~1 h after sporulation initiation; activity is confined to the prespore even when protein is present in both compartments (immunostaining and gpr-lacZ reporters) (Genes to Cells, 1996-10; https://doi.org/10.1046/j.1365-2443.1996.750275.x) (lewis1996compartmentalizeddistributionof pages 6-8).
- Molecular contacts: SpoIIAB–σF binding interfaces map to σ70 conserved regions 2.1, 3.1, and 4.1 (Genes Dev., 1996-09; https://doi.org/10.1101/gad.10.18.2348) (lewis1996compartmentalizeddistributionof pages 6-8).
- Anti-sigma binding and kinase activity: SpoIIAB binds σF to inhibit transcription and has serine kinase activity that phosphorylates SpoIIAA, toggling σF release via partner switching (PNAS, 1993-03; https://doi.org/10.1073/pnas.90.6.2325) (haldenwang1995thesigmafactors pages 17-18).
- Septation-coupled activation: SpoIIE at the division septum dephosphorylates SpoIIAA-P, enabling compartment-restricted σF activation (Genes Dev., 1999-05; https://doi.org/10.1101/gad.13.9.1156) (lewis1996compartmentalizeddistributionof pages 6-8).
- σF-dependent forespore promoter architecture and function (2024): For rho, a SigF-like −10 (GGTAAAAATA) and GAATA −35 with a 14-bp A/T-rich spacer operate in forespores; mutating the −35 element (mF-35T/A or mF-35T/C) abolishes forespore GFP bursts and reduces luciferase signals, recapitulating ΔsigF effects; ΔsigE does not impair forespore rho expression (JBC, 2024-12; https://doi.org/10.1016/j.jbc.2024.107905) (bidnenko2024complexsporulationspecificexpression pages 6-7, bidnenko2024complexsporulationspecificexpression pages 4-6).
- σF-driven regulon link: σF drives initial transcription of sigG in the forespore, coordinating the early-to-late switch in forespore gene expression; CsfB-based discrimination (E39 in σF vs N45 in σG) helps prevent premature σG activity (PLOS Genet., 2015-04; https://doi.org/10.1371/journal.pgen.1005104) (serrano2015dualspecificityantisigmafactor pages 2-4, serrano2015dualspecificityantisigmafactor pages 19-20).
- DNA repair targets under forespore control (2024): σF-dependent YwjD endonuclease incises the 5´ side of CPDs, 6–4 PDs, and DWIs in sporulating cells; subsequent lesion-specific processing enzymes (e.g., YqjH/YqjW, YpcP) act in a compartment-aware manner; multiple repair proteins are expressed in sporulation and packaged into spores (MMBR, 2024-06; https://doi.org/10.1128/mmbr.00158-23) (pedrazareyes2024bacillussubtilisstressassociated pages 18-20).
Mechanistic pathway and localization summary
σF is synthesized from the spoIIA operon alongside SpoIIAA and SpoIIAB. Before septation, SpoIIAB binds σF and, as a kinase, keeps SpoIIAA predominantly phosphorylated (SpoIIAA-P), maintaining σF inactive. Upon asymmetric septation, SpoIIE (at the septum) dephosphorylates SpoIIAA-P preferentially in the forespore, freeing SpoIIAA to bind SpoIIAB and release σF, thereby enabling σF–RNAP holoenzyme formation and forespore-restricted transcription. σF initiates early forespore programs, including sigG transcription and σF-dependent genes such as the forespore promoter of rho, while anti-sigma factor CsfB further enforces proper timing by discriminating among sporulation σ factors to prevent ectopic σG activation (haldenwang1995thesigmafactors pages 17-18, lewis1996compartmentalizeddistributionof pages 6-8, serrano2015dualspecificityantisigmafactor pages 2-4, serrano2015dualspecificityantisigmafactor pages 19-20, bidnenko2024complexsporulationspecificexpression pages 4-6, bidnenko2024complexsporulationspecificexpression pages 6-7, bidnenko2024complexsporulationspecificexpression pages 10-11).
Embedded artifact
| Component | Role in pathway | Cell compartment / timing | Mechanism or key molecular detail | Selected quantitative / structural data | Primary sources (with year) |
|---|---|---|---|---|---|
| SigF (spoIIAC) | Early forespore-specific sigma factor that initiates forespore transcriptional program | Activated in forespore; protein detectable ~1 h after sporulation onset | Member of sigma-70 family; directs RNAP to early forespore promoters; autoregulates spoIIA expression | Protein levels rise early in sporulation; forespore-restricted activity though protein may be present in both compartments (detectable ~1 h) | Haldenwang 1995 (haldenwang1995thesigmafactors pages 17-18); Lewis 1996 (lewis1996compartmentalizeddistributionof pages 6-8); Serrano 2015 (serrano2015dualspecificityantisigmafactor pages 2-4); Pedraza-Reyes 2024 (pedrazareyes2024bacillussubtilisstressassociated pages 18-20) |
| SpoIIAB | Anti-sigma factor and regulator (inhibits σF) | Cotranscribed with spoIIAC; acts prior to/around septation | Binds and sequesters σF to prevent holoenzyme formation; has serine kinase activity that phosphorylates SpoIIAA (controls partner-switching) | Binding interfaces map to conserved sigma regions (functional inhibition/kinase activity described) | Ayala et al. 2020 (ayala2020thestressresponsivealternative pages 2-3); Haldenwang 1995 (haldenwang1995thesigmafactors pages 17-18) |
| SpoIIAA | Anti–anti-sigma factor (antagonizes SpoIIAB) | Present in prespore/mother-cell; activity toggled by phosphorylation state | Unphosphorylated SpoIIAA binds SpoIIAB, releasing σF; SpoIIAB phosphorylates SpoIIAA (SpoIIAA-P) to inactivate it | Partner-switching cycle central to σF activation; biochemical assays demonstrate phosphorylation/dephosphorylation cycle | Ayala et al. 2020 (ayala2020thestressresponsivealternative pages 2-3); Lewis 1996 (lewis1996compartmentalizeddistributionof pages 6-8) |
| SpoIIE | Phosphatase that triggers σF activation in forespore | Localized to sporulation septum; acts at/after asymmetric septation to create forespore-specific signal | Dephosphorylates SpoIIAA-P at septum → frees SpoIIAA to antagonize SpoIIAB → σF activation in forespore | Septum-associated localization and septation-coupled activation; morphological checkpoint links SpoIIE activity to compartmentalized transcription | Arigoni/King reviews & experimental work summarized in Haldenwang 1995 and later reviews (haldenwang1995thesigmafactors pages 17-18, pedrazareyes2024bacillussubtilisstressassociated pages 18-20); Lewis 1996 (lewis1996compartmentalizeddistributionof pages 6-8) |
| CsfB (Gin) | Dual-specificity anti-sigma factor that reinforces cell-type specificity | Expressed early in forespore under σF control and later in mother cell under σK control | Binds selectively to closely related sporulation sigmas; discriminates σF vs σG via residue in region 2.1 (E39 in σF vs N45 in σG) to prevent ectopic σG activation | Reported spore formation efficiencies: PsigF/PsigK mutant comparisons (examples: WT ~83%; PsigF 77%; PsigK 88% reported) | Serrano et al. 2015 (serrano2015dualspecificityantisigmafactor pages 2-4, serrano2015dualspecificityantisigmafactor pages 6-7, serrano2015dualspecificityantisigmafactor pages 19-20) |
| csfB promoter | Target promoter used to control CsfB expression and timing | Recognized/initiated in forespore early (σF) and later in mother cell (σK); in vitro run-off transcription observed | Both σF- and σG-containing holoenzymes can initiate csfB transcription; promoter architecture allows stage-specific expression | In vitro reconstituted transcription produced a 148-nt run-off product with σF/σG holoenzymes (used in promoter assays) | Serrano et al. 2015 (serrano2015dualspecificityantisigmafactor pages 6-7) |
| spoIIA operon (tricistronic: spoIIAA–spoIIAB–spoIIAC) | Genetic unit encoding the SpoIIAA / SpoIIAB / SigF regulatory module | Transcribed prior to septation; autoregulated by σF from a spoIIA promoter | Tricistronic organization couples synthesis of anti-anti, anti, and σF; promoter includes upstream regulatory sequence enabling autoregulation | Genetic mapping/cloning established spoIIAC as σF (sequence similarity to sigma factors) | Haldenwang 1995 (haldenwang1995thesigmafactors pages 17-18); Lewis 1996 (lewis1996compartmentalizeddistributionof pages 6-8) |
Table: Compact summary table of the key components controlling Bacillus subtilis σF (spoIIAC) activation, their roles, compartmental timing, molecular mechanisms, and selected quantitative/structural notes with primary source citations for each entry.
Verification against the user’s CRITICAL identity checks
- Gene/protein symbol and description: The literature consistently identifies spoIIAC (sigF) as the sporulation sigma factor σF of Bacillus subtilis, matching the UniProt description for P07860 (RNA polymerase sigma-F, sporulation sigma factor, Stage II sporulation protein AC) (haldenwang1995thesigmafactors pages 17-18).
- Organism: All cited studies investigate σF in Bacillus subtilis; no evidence was found for a different organism under this symbol within the collected evidence, and no contradictory usage was identified. Where explicitly stated, the work is in B. subtilis (haldenwang1995thesigmafactors pages 17-18, lewis1996compartmentalizeddistributionof pages 6-8, bidnenko2024complexsporulationspecificexpression pages 4-6).
- Family and domains: σF is a σ70-family sigma factor; contact mapping with its anti-sigma (SpoIIAB) involves conserved σ70 regions 2.1, 3.1, and 4.1, consistent with σ70 architecture (lewis1996compartmentalizeddistributionof pages 6-8). We found no conflicting literature assigning different domains to sigF.
- Ambiguity check: The search returned no evidence of a different gene/protein designated “sigF” in a way that would confound Bacillus subtilis σF within this context; thus, we proceeded with the Bacillus subtilis σF literature exclusively (haldenwang1995thesigmafactors pages 17-18, lewis1996compartmentalizeddistributionof pages 6-8, bidnenko2024complexsporulationspecificexpression pages 4-6).
Selected source list with URLs and dates
- Haldenwang WG. The sigma factors of Bacillus subtilis. Microbiological Reviews. 1995-03. https://doi.org/10.1128/mr.59.1.1-30.1995 (haldenwang1995thesigmafactors pages 17-18)
- Duncan L, Losick R. SpoIIAB is an anti-sigma factor that binds and inhibits σF. PNAS. 1993-03. https://doi.org/10.1073/pnas.90.6.2325 (haldenwang1995thesigmafactors pages 17-18)
- Lewis PJ, Magnin T, Errington J. Compartmentalized distribution controlling σF. Genes to Cells. 1996-10. https://doi.org/10.1046/j.1365-2443.1996.750275.x (lewis1996compartmentalizeddistributionof pages 6-8)
- King N et al. Septation, dephosphorylation, and σF activation. Genes & Development. 1999-05. https://doi.org/10.1101/gad.13.9.1156 (lewis1996compartmentalizeddistributionof pages 6-8)
- Decatur L, Losick R. Three σF–SpoIIAB contact sites in σ70 regions. Genes & Development. 1996-09. https://doi.org/10.1101/gad.10.18.2348 (lewis1996compartmentalizeddistributionof pages 6-8)
- Serrano M et al. Dual-specificity anti-sigma CsfB discriminates σF/σG. PLoS Genetics. 2015-04. https://doi.org/10.1371/journal.pgen.1005104 (serrano2015dualspecificityantisigmafactor pages 2-4, serrano2015dualspecificityantisigmafactor pages 6-7, serrano2015dualspecificityantisigmafactor pages 19-20)
- Bidnenko V et al. Sporulation-specific, compartmental rho expression via SigF and SigH/Spo0A~P. JBC. 2024-12. https://doi.org/10.1016/j.jbc.2024.107905 (bidnenko2024complexsporulationspecificexpression pages 4-6, bidnenko2024complexsporulationspecificexpression pages 6-7, bidnenko2024complexsporulationspecificexpression pages 10-11, bidnenko2024complexsporulationspecificexpression pages 3-4, bidnenko2024complexsporulationspecificexpression pages 1-2, bidnenko2024complexsporulationspecificexpression pages 12-13)
- Pedraza-Reyes M et al. Stress-associated mutagenesis and developmental DNA repair with σF-linked forespore expression. MMBR. 2024-06. https://doi.org/10.1128/mmbr.00158-23 (pedrazareyes2024bacillussubtilisstressassociated pages 18-20)
Conclusions
σF (SigF/SpoIIAC) is the archetypal forespore-specific σ70-family sigma factor of Bacillus subtilis that initiates the early forespore transcriptional program after septation. Its activity is gated by a partner-switching module (SpoIIAB/SpoIIAA) under the control of the septal phosphatase SpoIIE, ensuring activation exclusively in the forespore. New 2024 work shows that σF directly establishes forespore transcription of the essential factor Rho from a dedicated σF promoter, while mother-cell rho expression is supplied by SigH/Spo0A~P-driven read-through, together sustaining spore morphogenesis and fitness. These developments, together with recent syntheses linking σF to forespore DNA repair and spore quality, refine the view of σF as both a fate determinant and a coordinator of forespore physiology with consequences for spore robustness and revival (haldenwang1995thesigmafactors pages 17-18, lewis1996compartmentalizeddistributionof pages 6-8, bidnenko2024complexsporulationspecificexpression pages 4-6, bidnenko2024complexsporulationspecificexpression pages 6-7, bidnenko2024complexsporulationspecificexpression pages 10-11, pedrazareyes2024bacillussubtilisstressassociated pages 18-20, serrano2015dualspecificityantisigmafactor pages 2-4).
References
(haldenwang1995thesigmafactors pages 17-18): W G Haldenwang. The sigma factors of bacillus subtilis. Microbiological Reviews, 59:1-30, Mar 1995. URL: https://doi.org/10.1128/mr.59.1.1-30.1995, doi:10.1128/mr.59.1.1-30.1995. This article has 790 citations.
(lewis1996compartmentalizeddistributionof pages 6-8): Peter J. Lewis, Thierry Magnin, and Jeffery Errington. Compartmentalized distribution of the proteins controlling the prespore‐specific transcription factor σf of bacillus subtilis. Genes to Cells, 1:881-894, Oct 1996. URL: https://doi.org/10.1046/j.1365-2443.1996.750275.x, doi:10.1046/j.1365-2443.1996.750275.x. This article has 54 citations and is from a peer-reviewed journal.
(serrano2015dualspecificityantisigmafactor pages 2-4): Mónica Serrano, JinXin Gao, João Bota, Ashley R. Bate, Jeffrey Meisner, Patrick Eichenberger, Charles P. Moran, and Adriano O. Henriques. Dual-specificity anti-sigma factor reinforces control of cell-type specific gene expression in bacillus subtilis. PLOS Genetics, 11:e1005104, Apr 2015. URL: https://doi.org/10.1371/journal.pgen.1005104, doi:10.1371/journal.pgen.1005104. This article has 17 citations and is from a domain leading peer-reviewed journal.
(bidnenko2024complexsporulationspecificexpression pages 11-12): Vladimir Bidnenko, Arnaud Chastanet, Christine Péchoux, Yulia Redko-Hamel, Olivier Pellegrini, Sylvain Durand, Ciarán Condon, Marc Boudvillain, Matthieu Jules, and Elena Bidnenko. Complex sporulation-specific expression of transcription termination factor rho highlights its involvement in bacillus subtilis cell differentiation. Journal of Biological Chemistry, 300:107905, Dec 2024. URL: https://doi.org/10.1016/j.jbc.2024.107905, doi:10.1016/j.jbc.2024.107905. This article has 6 citations and is from a domain leading peer-reviewed journal.
(bidnenko2024complexsporulationspecificexpression pages 3-4): Vladimir Bidnenko, Arnaud Chastanet, Christine Péchoux, Yulia Redko-Hamel, Olivier Pellegrini, Sylvain Durand, Ciarán Condon, Marc Boudvillain, Matthieu Jules, and Elena Bidnenko. Complex sporulation-specific expression of transcription termination factor rho highlights its involvement in bacillus subtilis cell differentiation. Journal of Biological Chemistry, 300:107905, Dec 2024. URL: https://doi.org/10.1016/j.jbc.2024.107905, doi:10.1016/j.jbc.2024.107905. This article has 6 citations and is from a domain leading peer-reviewed journal.
(bidnenko2024complexsporulationspecificexpression pages 4-6): Vladimir Bidnenko, Arnaud Chastanet, Christine Péchoux, Yulia Redko-Hamel, Olivier Pellegrini, Sylvain Durand, Ciarán Condon, Marc Boudvillain, Matthieu Jules, and Elena Bidnenko. Complex sporulation-specific expression of transcription termination factor rho highlights its involvement in bacillus subtilis cell differentiation. Journal of Biological Chemistry, 300:107905, Dec 2024. URL: https://doi.org/10.1016/j.jbc.2024.107905, doi:10.1016/j.jbc.2024.107905. This article has 6 citations and is from a domain leading peer-reviewed journal.
(bidnenko2024complexsporulationspecificexpression pages 6-7): Vladimir Bidnenko, Arnaud Chastanet, Christine Péchoux, Yulia Redko-Hamel, Olivier Pellegrini, Sylvain Durand, Ciarán Condon, Marc Boudvillain, Matthieu Jules, and Elena Bidnenko. Complex sporulation-specific expression of transcription termination factor rho highlights its involvement in bacillus subtilis cell differentiation. Journal of Biological Chemistry, 300:107905, Dec 2024. URL: https://doi.org/10.1016/j.jbc.2024.107905, doi:10.1016/j.jbc.2024.107905. This article has 6 citations and is from a domain leading peer-reviewed journal.
(bidnenko2024complexsporulationspecificexpression pages 10-11): Vladimir Bidnenko, Arnaud Chastanet, Christine Péchoux, Yulia Redko-Hamel, Olivier Pellegrini, Sylvain Durand, Ciarán Condon, Marc Boudvillain, Matthieu Jules, and Elena Bidnenko. Complex sporulation-specific expression of transcription termination factor rho highlights its involvement in bacillus subtilis cell differentiation. Journal of Biological Chemistry, 300:107905, Dec 2024. URL: https://doi.org/10.1016/j.jbc.2024.107905, doi:10.1016/j.jbc.2024.107905. This article has 6 citations and is from a domain leading peer-reviewed journal.
(pedrazareyes2024bacillussubtilisstressassociated pages 18-20): Mario Pedraza-Reyes, Karen Abundiz-Yañez, Alejandra Rangel-Mendoza, Lissett E. Martínez, Rocío C. Barajas-Ornelas, Mayra Cuéllar-Cruz, Hilda C. Leyva-Sánchez, Víctor M. Ayala-García, Luz I. Valenzuela-García, and Eduardo A. Robleto. bacillus subtilis stress-associated mutagenesis and developmental dna repair. Microbiology and Molecular Biology Reviews, Jun 2024. URL: https://doi.org/10.1128/mmbr.00158-23, doi:10.1128/mmbr.00158-23. This article has 18 citations and is from a domain leading peer-reviewed journal.
(serrano2015dualspecificityantisigmafactor pages 19-20): Mónica Serrano, JinXin Gao, João Bota, Ashley R. Bate, Jeffrey Meisner, Patrick Eichenberger, Charles P. Moran, and Adriano O. Henriques. Dual-specificity anti-sigma factor reinforces control of cell-type specific gene expression in bacillus subtilis. PLOS Genetics, 11:e1005104, Apr 2015. URL: https://doi.org/10.1371/journal.pgen.1005104, doi:10.1371/journal.pgen.1005104. This article has 17 citations and is from a domain leading peer-reviewed journal.
(serrano2015dualspecificityantisigmafactor pages 6-7): Mónica Serrano, JinXin Gao, João Bota, Ashley R. Bate, Jeffrey Meisner, Patrick Eichenberger, Charles P. Moran, and Adriano O. Henriques. Dual-specificity anti-sigma factor reinforces control of cell-type specific gene expression in bacillus subtilis. PLOS Genetics, 11:e1005104, Apr 2015. URL: https://doi.org/10.1371/journal.pgen.1005104, doi:10.1371/journal.pgen.1005104. This article has 17 citations and is from a domain leading peer-reviewed journal.
(bidnenko2024complexsporulationspecificexpression pages 1-2): Vladimir Bidnenko, Arnaud Chastanet, Christine Péchoux, Yulia Redko-Hamel, Olivier Pellegrini, Sylvain Durand, Ciarán Condon, Marc Boudvillain, Matthieu Jules, and Elena Bidnenko. Complex sporulation-specific expression of transcription termination factor rho highlights its involvement in bacillus subtilis cell differentiation. Journal of Biological Chemistry, 300:107905, Dec 2024. URL: https://doi.org/10.1016/j.jbc.2024.107905, doi:10.1016/j.jbc.2024.107905. This article has 6 citations and is from a domain leading peer-reviewed journal.
(bidnenko2024complexsporulationspecificexpression pages 12-13): Vladimir Bidnenko, Arnaud Chastanet, Christine Péchoux, Yulia Redko-Hamel, Olivier Pellegrini, Sylvain Durand, Ciarán Condon, Marc Boudvillain, Matthieu Jules, and Elena Bidnenko. Complex sporulation-specific expression of transcription termination factor rho highlights its involvement in bacillus subtilis cell differentiation. Journal of Biological Chemistry, 300:107905, Dec 2024. URL: https://doi.org/10.1016/j.jbc.2024.107905, doi:10.1016/j.jbc.2024.107905. This article has 6 citations and is from a domain leading peer-reviewed journal.
(ayala2020thestressresponsivealternative pages 2-3): Facundo Rodriguez Ayala, Marco Bartolini, and Roberto Grau. The stress-responsive alternative sigma factor sigb of bacillus subtilis and its relatives: an old friend with new functions. Frontiers in Microbiology, Sep 2020. URL: https://doi.org/10.3389/fmicb.2020.01761, doi:10.3389/fmicb.2020.01761. This article has 112 citations and is from a poor quality or predatory journal.
Source: sigF-deep-research-bioreason-rl.md
The BioReason functional summary reads:
A cytoplasmic initiation factor that redirects bacterial transcription toward sporulation programs. It binds bacterial RNA polymerase and engages promoter DNA via a modular sigma-70 fold, using distinct recognition and melting elements to assemble open complexes at sporulation promoters. By selecting and activating the appropriate initiation sites, it drives developmental transcription required for the formation and maturation of spores.
The summary correctly identifies SigF as a sigma factor with sigma-70 architecture that drives sporulation-associated transcription. The description of promoter recognition and open complex formation aligns with sigma factor activity (GO:0016987) and DNA-templated transcription initiation (GO:0006352). The sporulation connection is correct (GO:0030435).
However, the summary has notable gaps:
Missing compartment specificity: SigF is specifically the first forespore-specific sigma factor, activated exclusively in the forespore compartment after asymmetric septation. The BioReason summary generically says "sporulation programs" without capturing this critical compartment-specific activation that distinguishes SigF from other sporulation sigma factors.
Missing regulatory mechanism: The partner-switching mechanism (SpoIIAB anti-sigma factor, SpoIIAA anti-anti-sigma factor, SpoIIE phosphatase) is the hallmark of SigF regulation and is completely absent. The curated review identifies the sigma factor antagonist complex (GO:1903865) as a core annotation.
Incorrect GO predictions: BioReason's predicted GO terms include cell wall (GO:0005618), plasma membrane (GO:0005886), spore wall (GO:0031160), and cell periphery (GO:0071944) as cellular components -- these are all incorrect for a cytoplasmic sigma factor. The curated review notes cytoplasmic localization.
Missing specific regulon: SigF directs transcription of sigG, csfB, and the forespore-specific rho promoter. None of this specificity is captured.
Comparison with interpro2go:
The interpro2go annotations for sigF include DNA-binding transcription factor activity (GO:0003700), which the curated review flags as incorrect for sigma factors (should be GO:0016987, sigma factor activity). BioReason correctly identifies sigma factor activity in its thinking trace but oddly lists protein binding (GO:0005515) as the MF GO term rather than sigma factor activity. The BP predictions from interpro2go include broad regulatory terms, which BioReason recapitulates. BioReason's functional summary narrative is more informative than interpro2go, but the GO term predictions contain errors not present in interpro2go (e.g., membrane/cell wall CC terms).
The trace correctly identifies sigma-70 regions 2, 3, and 4 and their roles in promoter recognition and RNAP binding. The identification of sigma-B/F/G family signatures correctly places SigF in the sporulation sigma factor clade. However, the trace does not leverage this clade information to identify forespore-specific function.
id: P07860
gene_symbol: sigF
product_type: PROTEIN
status: DRAFT
taxon:
id: NCBITaxon:224308
label: Bacillus subtilis (strain 168)
description: >-
SigF (also known as SpoIIAC) encodes the RNA polymerase sigma-F factor, a member of the sigma-70 family
of alternative sigma factors that is specifically activated in the forespore compartment during Bacillus
subtilis sporulation. SigF is the first compartment-specific transcription factor activated after asymmetric
septation, initiating the early forespore transcriptional program. The protein contains conserved sigma-70
regions (2, 3, and 4) including a helix-turn-helix DNA-binding motif that recognizes specific promoter
sequences. SigF activity is tightly controlled by an elegant partner-switching mechanism involving the
anti-sigma factor SpoIIAB (which binds and sequesters SigF) and the anti-anti-sigma factor SpoIIAA. Before
septation, SpoIIAB keeps SigF inactive by direct binding and also phosphorylates SpoIIAA to prevent its
antagonistic activity. Upon asymmetric septation, the membrane-associated phosphatase SpoIIE preferentially
dephosphorylates SpoIIAA-P in the forespore, allowing unphosphorylated SpoIIAA to bind SpoIIAB and release
SigF for holoenzyme formation. This partner-switching mechanism ensures compartment-specific activation of
SigF exclusively in the forespore despite the protein being present in both compartments. SigF directs
transcription of early forespore genes including sigG (the late forespore sigma factor), csfB (an anti-sigma
factor that reinforces cell-type specificity), and the forespore-specific promoter of rho (transcription
termination factor). SigF also autoregulates the spoIIA operon from which it is expressed. The sequential
activation of sigma factors (SigF in forespore, SigE in mother cell, followed by SigG and SigK) orchestrates
the complex developmental program of sporulation.
existing_annotations:
- term:
id: GO:0000976
label: transcription cis-regulatory region binding
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
Sigma factors bind to specific promoter sequences to position RNA polymerase for transcription initiation.
SigF recognizes and binds to SigF-dependent promoter elements consisting of a -10 region (consensus similar
to GGTAAAAATA) and a -35 region (GAATA) separated by an A/T-rich spacer. This has been demonstrated through
mutational analysis of the forespore-specific rho promoter where mutations in the -35 GAATA element abolished
forespore-specific transcription (Bidnenko et al. 2024). The helix-turn-helix motif in SigF (residues 221-240
per UniProt) mediates DNA binding.
action: ACCEPT
reason: >-
The IBA annotation for transcription cis-regulatory region binding is well-supported by the molecular
function of sigma factors. SigF contains a characterized helix-turn-helix DNA-binding motif and has
demonstrated sequence-specific recognition of promoter elements. The 2024 work on the rho promoter
provides direct evidence that SigF recognizes specific DNA sequences at its target promoters.
supported_by:
- reference_id: file:BACSU/sigF/sigF-deep-research-falcon.md
supporting_text: "a SigF-like -10 (GGTAAAAATA) and GAATA -35 separated by an A/T-rich spacer were identified; mutation of the -35 GAATA element abolished the forespore GFP burst and reduced luciferase activity"
- reference_id: UniProt:P07860
supporting_text: "InterPro; IPR001387; Cro/C1-type_HTH"
- term:
id: GO:0003899
label: DNA-directed RNA polymerase activity
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
This annotation suggests SigF has RNA polymerase catalytic activity, which is inaccurate. Sigma factors
do not possess intrinsic polymerase activity - they are initiation factors that confer promoter specificity
to the RNA polymerase core enzyme. The catalytic activity resides in the core RNAP subunits (alpha, beta,
beta-prime), not in sigma factors.
action: REMOVE
reason: >-
Sigma factors including SigF do not catalyze RNA synthesis. They function as specificity factors that
direct the RNA polymerase holoenzyme to specific promoters. The RNAP core enzyme provides the catalytic
activity. This annotation conflates the function of the sigma subunit with the catalytic core. The correct
annotation is sigma factor activity (GO:0016987), which is already present.
supported_by:
- reference_id: UniProt:P07860
supporting_text: "Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released"
- term:
id: GO:0006355
label: regulation of DNA-templated transcription
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
SigF regulates transcription by conferring promoter specificity to RNA polymerase, thereby activating
a specific set of forespore genes during sporulation. SigF directs expression of numerous sporulation-specific
genes including sigG, csfB, and the forespore promoter of rho. SigF also autoregulates the spoIIA operon.
action: ACCEPT
reason: >-
As an alternative sigma factor, SigF fundamentally regulates transcription by determining which promoters
the RNAP holoenzyme can recognize. SigF-dependent transcription activates the early forespore program.
This is a core function of sigma factors and is well-documented for SigF.
supported_by:
- reference_id: UniProt:P07860
supporting_text: "This sigma factor is responsible for the expression of sporulation specific genes"
- term:
id: GO:0016987
label: sigma factor activity
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
SigF is a well-characterized sigma factor of the sigma-70 family. It contains conserved sigma-70 regions
(regions 2, 3, and 4) that mediate core RNAP binding and promoter recognition. Biochemical and genetic
studies have definitively established SigF as a sigma factor that associates with RNAP core and directs
transcription initiation at SigF-dependent promoters.
action: ACCEPT
reason: >-
This is the primary molecular function of SigF. The sigma factor activity annotation accurately captures
SigF's role in conferring promoter specificity to RNA polymerase. This is supported by extensive biochemical
characterization, domain analysis, and genetic studies demonstrating SigF-dependent transcription.
supported_by:
- reference_id: UniProt:P07860
supporting_text: "Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released"
- reference_id: UniProt:P07860
supporting_text: "Associates with the RNAP core only in stationary phase cells"
- term:
id: GO:1903865
label: sigma factor antagonist complex
evidence_type: IBA
original_reference_id: GO_REF:0000033
review:
summary: >-
SigF forms a complex with its anti-sigma factor SpoIIAB, which inhibits SigF activity by direct binding.
The SigF-SpoIIAB complex represents a sigma factor antagonist complex where SpoIIAB sequesters SigF and
prevents holoenzyme formation. This complex is a central component of the partner-switching mechanism
that controls SigF activation.
action: ACCEPT
reason: >-
The formation of a SigF-SpoIIAB inhibitory complex is well-documented and represents a key regulatory
mechanism. SpoIIAB binds SigF through contacts at conserved sigma-70 regions 2.1, 3.1, and 4.1. This
complex formation is essential for keeping SigF inactive in the pre-divisional cell and in the mother
cell compartment after septation.
supported_by:
- reference_id: UniProt:P07860
supporting_text: "Interaction with SpoIIAB inhibits sigma-F activity throughout the cell before the formation of the asymmetric septum"
- term:
id: GO:0003677
label: DNA binding
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: >-
SigF binds DNA as part of the RNAP holoenzyme to recognize promoter sequences. SigF contains a characterized
helix-turn-helix DNA-binding motif (residues 221-240) that mediates sequence-specific recognition of
SigF-dependent promoters.
action: ACCEPT
reason: >-
While this IEA annotation is more general than the IBA annotation for transcription cis-regulatory region
binding (GO:0000976), it is not incorrect. Sigma factors do bind DNA as part of the holoenzyme. The
presence of a characterized HTH motif in SigF supports this annotation. This can be retained as a broader
annotation alongside the more specific term.
supported_by:
- reference_id: UniProt:P07860
supporting_text: "InterPro; IPR001387; Cro/C1-type_HTH"
- term:
id: GO:0003700
label: DNA-binding transcription factor activity
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >-
This term is intended for sequence-specific DNA-binding transcription factors that regulate transcription
by binding to cis-regulatory elements. While sigma factors do bind DNA and regulate transcription, they
function mechanistically differently from classical transcription factors - sigma factors confer promoter
recognition to the RNA polymerase core rather than acting as independent regulatory factors.
action: MODIFY
reason: >-
The term GO:0003700 is designed for classical transcription factors that independently bind DNA regulatory
elements. Sigma factors have a distinct mechanism - they are subunits of the RNAP holoenzyme that confer
promoter specificity. The more appropriate and specific term is GO:0016987 (sigma factor activity), which
is already annotated. This IEA annotation from InterPro mapping may be overly broad.
proposed_replacement_terms:
- id: GO:0016987
label: sigma factor activity
supported_by:
- reference_id: UniProt:P07860
supporting_text: "Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released"
- term:
id: GO:0006351
label: DNA-templated transcription
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >-
SigF participates in DNA-templated transcription as the sigma subunit of the RNA polymerase holoenzyme.
As a sigma factor, it enables transcription initiation at SigF-dependent promoters during sporulation.
action: ACCEPT
reason: >-
This biological process annotation correctly captures SigF's involvement in transcription. As a sigma
factor, SigF is directly involved in the transcription process by conferring promoter specificity to
RNAP and enabling transcription initiation.
supported_by:
- reference_id: UniProt:P07860
supporting_text: "Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites"
- reference_id: UniProt:P07860
supporting_text: "This sigma factor is responsible for the expression of sporulation specific genes"
- term:
id: GO:0006352
label: DNA-templated transcription initiation
evidence_type: IEA
original_reference_id: GO_REF:0000002
review:
summary: >-
SigF is specifically involved in transcription initiation - sigma factors function at the initiation
step to position RNA polymerase at promoters and enable formation of the open complex. After initiation,
sigma factors are typically released from the elongating polymerase.
action: ACCEPT
reason: >-
This annotation is highly appropriate for SigF. Sigma factors function specifically at the transcription
initiation step - they enable promoter recognition and open complex formation but are released during
the transition to elongation. This term accurately captures the specific stage of transcription where
sigma factors act.
supported_by:
- reference_id: UniProt:P07860
supporting_text: "Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released"
- term:
id: GO:0006355
label: regulation of DNA-templated transcription
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: >-
Duplicate annotation with the IBA entry. SigF regulates transcription by determining which promoters
are recognized by the RNAP holoenzyme, thereby activating transcription of forespore-specific genes.
action: ACCEPT
reason: >-
This is a valid annotation for SigF regardless of evidence code. As an alternative sigma factor, SigF
regulates transcription by conferring promoter specificity. The duplicate with different evidence codes
is acceptable and reflects independent inference paths reaching the same conclusion.
supported_by:
- reference_id: UniProt:P07860
supporting_text: "This sigma factor is responsible for the expression of sporulation specific genes"
- term:
id: GO:0016987
label: sigma factor activity
evidence_type: IEA
original_reference_id: GO_REF:0000120
review:
summary: >-
Duplicate annotation with the IBA entry. SigF is a well-characterized member of the sigma-70 family
with demonstrated sigma factor activity.
action: ACCEPT
reason: >-
This core molecular function annotation is appropriate for SigF. The duplicate with IEA evidence code
reflects independent computational inference confirming the phylogenetically-derived IBA annotation.
Duplicates with different evidence types are acceptable in GO annotation.
supported_by:
- reference_id: UniProt:P07860
supporting_text: "Belongs to the sigma-70 factor family"
- term:
id: GO:0030435
label: sporulation resulting in formation of a cellular spore
evidence_type: IEA
original_reference_id: GO_REF:0000043
review:
summary: >-
SigF plays an essential role in sporulation. It is the first compartment-specific sigma factor activated
during sporulation and initiates the early forespore transcriptional program. Mutations in sigF block
sporulation and prevent formation of mature spores.
action: ACCEPT
reason: >-
This biological process annotation appropriately captures SigF's essential role in sporulation. SigF
is absolutely required for spore formation - mutations abolish spore production and induction of
sporulation-associated enzymes. SigF initiates the forespore developmental program that ultimately
leads to spore formation.
supported_by:
- reference_id: UniProt:P07860
supporting_text: "In spo-63 (loss of residues 27-255); no spores develop, no induction of sporulation-associated enzymes"
- term:
id: GO:2000142
label: regulation of DNA-templated transcription initiation
evidence_type: IEA
original_reference_id: GO_REF:0000108
review:
summary: >-
SigF specifically regulates transcription at the initiation step. As a sigma factor, it enables
recognition of specific promoters and formation of the initiation complex. This term is more specific
than the general regulation of transcription term and accurately reflects sigma factor function.
action: ACCEPT
reason: >-
This annotation correctly captures that sigma factors regulate transcription specifically at the
initiation step. SigF enables RNAP to recognize and initiate transcription from SigF-dependent
promoters. This is a precise characterization of sigma factor function.
supported_by:
- reference_id: UniProt:P07860
supporting_text: "Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites"
references:
- id: GO_REF:0000002
title: Gene Ontology annotation through association of InterPro records with GO terms
findings: []
- id: GO_REF:0000033
title: Annotation inferences using phylogenetic trees
findings: []
- id: GO_REF:0000043
title: Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
findings: []
- id: GO_REF:0000108
title: Automatic assignment of GO terms using logical inference, based on inter-ontology links
findings: []
- id: GO_REF:0000120
title: Combined Automated Annotation using Multiple IEA Methods
findings: []
- id: PMID:3116160
title: "Structure and function in a Bacillus subtilis sporulation-specific sigma factor: molecular nature of mutations in spoIIAC"
full_text_unavailable: true
findings: []
- id: PMID:8358793
title: "Sigma F, the first compartment-specific transcription factor of B. subtilis, is regulated by an anti-sigma factor that is also a protein kinase"
full_text_unavailable: true
findings: []
- id: PMID:8759874
title: "Identification of additional genes under the control of the transcription factor sigma F of Bacillus subtilis"
full_text_unavailable: true
findings: []
- id: PMID:21037003
title: "A small protein required for the switch from sigma-F to sigma-G during sporulation in Bacillus subtilis"
full_text_unavailable: true
findings: []
- id: PMID:21710567
title: "The dynamic protein partnership of RNA polymerase in Bacillus subtilis"
full_text_unavailable: true
findings: []
- id: file:BACSU/sigF/sigF-deep-research-falcon.md
title: "Deep research review of sigF function and regulation"
findings:
- statement: SigF is the archetypal forespore-specific sigma-70-family sigma factor that initiates the early forespore transcriptional program after septation
- statement: SigF activity is gated by a partner-switching module (SpoIIAB/SpoIIAA) under the control of the septal phosphatase SpoIIE
- statement: SigF directly establishes forespore transcription of rho from a dedicated SigF promoter
core_functions:
- description: >-
SigF is the primary forespore-specific sigma factor that confers promoter recognition specificity
to RNA polymerase, enabling transcription of early forespore genes during sporulation. As a member
of the sigma-70 family, SigF binds to the RNAP core and directs the holoenzyme to SigF-dependent
promoters characterized by specific -10 and -35 elements.
molecular_function:
id: GO:0016987
label: sigma factor activity
directly_involved_in:
- id: GO:0006352
label: DNA-templated transcription initiation
- id: GO:0030435
label: sporulation resulting in formation of a cellular spore
supported_by:
- reference_id: UniProt:P07860
supporting_text: "Sigma factors are initiation factors that promote the attachment of RNA polymerase to specific initiation sites and are then released"
- reference_id: UniProt:P07860
supporting_text: "Associates with the RNAP core only in stationary phase cells"
- description: >-
SigF forms an inhibitory complex with the anti-sigma factor SpoIIAB, which is essential for
the partner-switching mechanism that controls compartment-specific SigF activation. SpoIIAB
binding to SigF prevents holoenzyme formation.
molecular_function:
id: GO:0016987
label: sigma factor activity
in_complex:
id: GO:1903865
label: sigma factor antagonist complex
supported_by:
- reference_id: UniProt:P07860
supporting_text: "Interaction with SpoIIAB inhibits sigma-F activity throughout the cell before the formation of the asymmetric septum"
suggested_questions:
- question: What is the complete SigF regulon and how does it compare across Bacillus species?
- question: How is the partner-switching mechanism quantitatively tuned to ensure reliable compartment-specific activation?
suggested_experiments:
- description: >-
ChIP-seq analysis of SigF binding during sporulation would enable genome-wide identification of
SigF binding sites, comprehensively defining the SigF regulon and revealing any previously
uncharacterized target promoters.
hypothesis: SigF binds to specific promoter sequences genome-wide to activate a defined early forespore transcriptional program
experiment_type: ChIP-seq
- description: >-
Quantitative analysis of SpoIIE phosphatase activity in forespore vs mother cell would illuminate
the molecular basis of compartment-specific SigF activation by understanding how SpoIIE activity
is restricted to the forespore.
hypothesis: SpoIIE phosphatase activity is higher in the forespore compartment due to its localization at the asymmetric septum
experiment_type: Biochemical assay