SpoIIAB is an anti-sigma factor and serine/threonine protein kinase that controls activation of the forespore-specific sigma factor sigma F during Bacillus subtilis sporulation. It binds sigma F to prevent RNA polymerase holoenzyme formation and phosphorylates the anti-anti-sigma factor SpoIIAA on a serine residue, contributing to the partner-switching mechanism that gates sigma F activity.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0016989 sigma factor antagonist activity | IBA GO_REF:0000033 | ACCEPT | Summary: SpoIIAB is the anti-sigma factor for sigma F, binding sigma F and blocking formation of the RNA polymerase holoenzyme. Reason: This is the defining molecular function of SpoIIAB. UniProt states that SpoIIAB binds sigma F and inhibits holoenzyme formation, consistent with sigma factor antagonist activity. Supporting Evidence: file:BACSU/spoIIAB/spoIIAB-uniprot.txt Binds to sigma F and blocks its ability to form an RNA polymerase holoenzyme (E-sigma F). |
| GO:0045892 negative regulation of DNA-templated transcription | IBA GO_REF:0000033 | ACCEPT | Summary: By binding sigma F and blocking holoenzyme formation, SpoIIAB inhibits sigma F-dependent transcription. Reason: SpoIIAB directly antagonizes sigma F and prevents RNA polymerase holoenzyme formation, which is a direct negative regulatory effect on transcription of sigma F-dependent genes. Supporting Evidence: file:BACSU/spoIIAB/spoIIAB-uniprot.txt Binds to sigma F and blocks its ability to form an RNA polymerase holoenzyme (E-sigma F). |
| GO:0000166 nucleotide binding | IEA GO_REF:0000043 | MODIFY | Summary: SpoIIAB is an ATP-dependent kinase with specific ATP-binding motifs. Reason: The term "nucleotide binding" is overly broad; SpoIIAB is an ATP-binding protein kinase. Use the more specific ATP binding term. Proposed replacements: ATP binding Supporting Evidence: file:BACSU/spoIIAB/spoIIAB-uniprot.txt KW ATP-binding; Direct protein sequencing; Kinase; Nucleotide-binding; |
| GO:0004672 protein kinase activity | IEA GO_REF:0000104 | MODIFY | Summary: SpoIIAB phosphorylates SpoIIAA on a serine residue, functioning as a protein serine/threonine kinase. Reason: The generic protein kinase activity term is too broad. SpoIIAB is a serine/threonine protein kinase (EC 2.7.11.1), so a more specific kinase term is appropriate. Proposed replacements: protein serine/threonine kinase activity protein serine kinase activity Supporting Evidence: file:BACSU/spoIIAB/spoIIAB-uniprot.txt Phosphorylates SpoIIAA on a serine residue. |
| GO:0004674 protein serine/threonine kinase activity | IEA GO_REF:0000120 | ACCEPT | Summary: SpoIIAB is a serine/threonine protein kinase that phosphorylates SpoIIAA. Reason: UniProt assigns EC 2.7.11.1 and reports SpoIIAB phosphorylates SpoIIAA on a serine residue, supporting serine/threonine kinase activity. Supporting Evidence: file:BACSU/spoIIAB/spoIIAB-uniprot.txt Phosphorylates SpoIIAA on a serine residue. |
| GO:0005524 ATP binding | IEA GO_REF:0000120 | ACCEPT | Summary: SpoIIAB binds ATP as part of its kinase catalytic mechanism. Reason: ATP binding is a core feature of SpoIIAB's kinase activity and is noted explicitly in UniProt keywords. Supporting Evidence: file:BACSU/spoIIAB/spoIIAB-uniprot.txt KW ATP-binding; Direct protein sequencing; Kinase; Nucleotide-binding; |
| GO:0010468 regulation of gene expression | IEA GO_REF:0000104 | MARK AS OVER ANNOTATED | Summary: SpoIIAB regulates expression indirectly by inhibiting sigma F, which controls sporulation gene transcription. Reason: The term is too general and adds little beyond the specific sigma factor antagonist activity and negative regulation of transcription terms. Supporting Evidence: file:BACSU/spoIIAB/spoIIAB-uniprot.txt Binds to sigma F and blocks its ability to form an RNA polymerase holoenzyme (E-sigma F). |
| GO:0016301 kinase activity | IEA GO_REF:0000043 | MARK AS OVER ANNOTATED | Summary: SpoIIAB is a protein kinase; however, this term is overly general. Reason: The more specific protein serine/threonine kinase activity is already supported. This generic term is redundant. Supporting Evidence: file:BACSU/spoIIAB/spoIIAB-uniprot.txt DE EC=2.7.11.1; |
| GO:0016740 transferase activity | IEA GO_REF:0000043 | MARK AS OVER ANNOTATED | Summary: SpoIIAB has kinase/transferase activity, but this term is too generic. Reason: Transferase activity is a very broad parent term and is not informative relative to the specific kinase annotations. Supporting Evidence: file:BACSU/spoIIAB/spoIIAB-uniprot.txt DE EC=2.7.11.1; |
| GO:0016989 sigma factor antagonist activity | IEA GO_REF:0000002 | ACCEPT | Summary: SpoIIAB antagonizes sigma F by binding to it and blocking holoenzyme formation. Reason: The InterPro-based inference aligns with SpoIIAB's known anti-sigma factor role and is supported by UniProt functional annotation. Supporting Evidence: file:BACSU/spoIIAB/spoIIAB-uniprot.txt Binds to sigma F and blocks its ability to form an RNA polymerase holoenzyme (E-sigma F). |
| GO:0030435 sporulation resulting in formation of a cellular spore | IEA GO_REF:0000043 | ACCEPT | Summary: SpoIIAB is a stage II sporulation protein and part of the sigma F regulatory pathway. Reason: UniProt assigns the sporulation keyword and names SpoIIAB as a stage II sporulation protein, supporting its role in spore formation. Supporting Evidence: file:BACSU/spoIIAB/spoIIAB-uniprot.txt DE AltName: Full=Stage II sporulation protein AB; file:BACSU/spoIIAB/spoIIAB-uniprot.txt KW ATP-binding; Direct protein sequencing; Kinase; Nucleotide-binding; Reference proteome; Serine/threonine-protein kinase; Sporulation; Transferase. |
| GO:0030436 asexual sporulation | IEA GO_REF:0000104 | ACCEPT | Summary: SpoIIAB functions in the asexual sporulation program of B. subtilis. Reason: Sporulation in B. subtilis is an asexual developmental process. SpoIIAB is a stage II sporulation protein required for proper sporulation regulation. Supporting Evidence: file:BACSU/spoIIAB/spoIIAB-uniprot.txt DE AltName: Full=Stage II sporulation protein AB; |
| GO:0042174 negative regulation of sporulation resulting in formation of a cellular spore | IEA GO_REF:0000002 | MARK AS OVER ANNOTATED | Summary: SpoIIAB restrains sigma F activation prior to septation, but this does not represent a general negative regulation of sporulation. Reason: SpoIIAB is required for proper timing of sigma F activity and sporulation, not for inhibiting sporulation overall. The term overstates its effect on the overall sporulation outcome. Supporting Evidence: file:BACSU/spoIIAB/spoIIAB-uniprot.txt Binds to sigma F and blocks its ability to form an RNA polymerase holoenzyme (E-sigma F). |
| GO:0045892 negative regulation of DNA-templated transcription | IEA GO_REF:0000002 | ACCEPT | Summary: SpoIIAB inhibits sigma F, leading to negative regulation of sigma F-dependent transcription. Reason: SpoIIAB directly binds sigma F and blocks RNA polymerase holoenzyme formation, which is a direct negative regulatory effect on transcription. Supporting Evidence: file:BACSU/spoIIAB/spoIIAB-uniprot.txt Binds to sigma F and blocks its ability to form an RNA polymerase holoenzyme (E-sigma F). |
| GO:0106310 protein serine kinase activity | IEA GO_REF:0000116 | ACCEPT | Summary: SpoIIAB phosphorylates SpoIIAA on a serine residue, consistent with serine protein kinase activity. Reason: UniProt reports SpoIIAB phosphorylates SpoIIAA on serine and assigns EC 2.7.11.1; this supports protein serine kinase activity. Supporting Evidence: file:BACSU/spoIIAB/spoIIAB-uniprot.txt Phosphorylates SpoIIAA on a serine residue. |
| GO:0005515 protein binding | IPI PMID:25278935 Cross-phosphorylation of bacterial serine/threonine and tyro... | UNDECIDED | Summary: The cited study examines kinase-kinase interactions and phosphorylation networks in B. subtilis and includes SpoIIAB in interaction assays, but the specific binding partner for SpoIIAB is not clearly stated here. Reason: The PMID describes broad kinase interaction and cross-phosphorylation assays and lists SpoIIAB among the proteins tested, but it does not provide a clear, specific binding interaction for SpoIIAB in the accessible text. More direct binding evidence would be needed to accept a generic protein binding annotation. Supporting Evidence: PMID:25278935 The genes encoding the BY-kinases (PtkA, PtkA) Hanks-type serine/threonine-kinases (PrkC, PrkD, YabT), two-component-like serine-kinases (SpoIIAB, RsbT, and RsbW), BY-kinase modulators (TkmA, TkmB) |
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Download this section (compressed HTML)Q: Do cross-phosphorylation events by Hanks-type kinases (e.g. PrkC, PrkD, YabT) on SpoIIAB reported in vitro (PMID:25278935) occur under physiological sporulation conditions in B. subtilis, and do they modulate the timing or amplitude of sigma F activation in the forespore?
Q: How is the septum-localized asymmetric release of sigma F from SpoIIAB coupled to SpoIIE phosphatase activity in the forespore, and what determines the precise threshold of SpoIIAA dephosphorylation required to titrate SpoIIAB and free sigma F?
Experiment: Introduce phospho-mimetic and phospho-null substitutions at SpoIIAB residues identified as cross-phosphorylation targets and measure sigma F activity in vivo (e.g. using a P_spoIIQ-lacZ or fluorescent reporter), SpoIIAA phosphorylation kinetics in vitro, and sporulation efficiency. Include ΞprkC/ΞprkD/ΞyabT backgrounds to test whether removing the donor kinases perturbs sigma F timing.
Hypothesis: Cross-phosphorylation of SpoIIAB by Hanks-type kinases modulates its anti-sigma-F activity or ATPase turnover during sporulation.
Type: Site-directed mutagenesis + reporter assay + genetic epistasis
Experiment: Use fluorescent tags on SpoIIAB and time-lapse microscopy of sporulating cells to quantify SpoIIAB abundance in mother cell versus forespore before and after septation. Combine with pulse-chase and protease-deficient backgrounds (e.g. ClpXP/LonA mutants) to test whether SpoIIAB turnover is asymmetric and protease-dependent.
Hypothesis: Compartment-specific SpoIIAB degradation contributes to release of sigma F in the forespore, in addition to SpoIIE-driven SpoIIAA dephosphorylation.
Type: Live-cell fluorescence microscopy + pulse-chase
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