Spo0J is the Bacillus subtilis ParB chromosome-partitioning protein, a CTP-binding DNA clamp and CTP hydrolase. It recognizes origin-proximal parS sites and spreads onto neighboring DNA, organizing a nucleoprotein platform that recruits the Smc-ScpAB chromosome-condensation machinery for efficient segregation. CTP binding supports clamp engagement and loading; hydrolysis is dispensable for the loading steps tested in vitro and has been proposed to promote turnover or recycling. Spo0J also regulates the Soj/ParA control system for DnaA-dependent replication initiation. Through antagonism of Soj and the replication checkpoint, it contributes positively to the initiation of sporulation.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005694 chromosome | IBA GO_REF:0000033 | ACCEPT | Summary: Spo0J associates with the origin-proximal nucleoid/chromosome. Reason: Direct microscopy and origin-proximal binding support the localization. The broad chromosome and nucleoid terms are consistent with the more specific bacterial-nucleoid observation. Supporting Evidence: PMID:9114058 Spo0J was associated with a region of the nucleoid proximal to the cell pole, both in growing cells dividing symmetrically and in sporulating cells dividing asymmetrically. file:BACSU/spo0J/spo0J-primary-scope.md leaf PTN002121226, below chromosome/segregation IBD PTN002121184 and positive-sporulation IBD PTN002121186. |
| GO:0007059 chromosome segregation | IBA GO_REF:0000033 | ACCEPT | Summary: Spo0J organizes chromosomes for faithful segregation. Reason: The anucleate-cell phenotype is supplemented by direct parS DNA binding/clamp activity and recruitment of the Smc machinery. Spo0J does structural and recruitment work in segregation; this is not an annotation based solely on loss-of-function necessity. Supporting Evidence: PMID:8071208 spo0J null mutants produced a significant proportion of anucleate cells during vegetative growth. PMID:31649139 A helix-turn-helix (HTH) motif in the middle domain (M) recognizes parS DNA. PMID:19450517 insertion of parS sites near the replication terminus targets SMC to this position leading to defects in chromosome organization and segregation. file:BACSU/spo0J/spo0J-primary-scope.md leaf PTN002121226, below chromosome/segregation IBD PTN002121184 and positive-sporulation IBD PTN002121186. |
| GO:0045881 positive regulation of sporulation resulting in formation of a cellular spore | IBA GO_REF:0000033 | ACCEPT | Summary: Spo0J positively contributes to sporulation initiation through Soj-dependent regulation. Reason: The source genetic suppression experiment establishes antagonism of Soj inhibition. A regulator can participate in sporulation without executing spore structural assembly. The later Soj-DnaA-Sda mechanism refines the route to Spo0A and does not make the broad sporulation annotation non-core or false. Supporting Evidence: PMID:8071208 These results indicate that Soj inhibits the initiation of sporulation and that Spo0J antagonizes that inhibition. PMID:19450516 Spo0J performs two independent functions: regulation of initiation of DNA replication via Soj and promotion of chromosome segregation by Smc recruitment. file:BACSU/spo0J/spo0J-primary-scope.md leaf PTN002121226, below chromosome/segregation IBD PTN002121184 and positive-sporulation IBD PTN002121186. |
| GO:0003677 DNA binding | IEA GO_REF:0000120 | ACCEPT | Summary: Spo0J binds DNA, including sequence-specific parS and nonspecific flanking DNA. Reason: The broad DNA-binding term accurately includes both recognition and spreading/clamp behavior. It should not be modified solely to make it more specific, and narrowing to centromeric recognition would lose the nonspecific component. Supporting Evidence: PMID:31649139 A helix-turn-helix (HTH) motif in the middle domain (M) recognizes parS DNA. PMID:31649139 Isothermal titration calorimetry (ITC) confirmed ParBBsu binding to CTP yielding dissociation constants (Kd) in the range of 10-50 ΞΌM. |
| GO:0007059 chromosome segregation | IEA GO_REF:0000043 | ACCEPT | Summary: Spo0J organizes chromosomes for faithful segregation. Reason: The anucleate-cell phenotype is supplemented by direct parS DNA binding/clamp activity and recruitment of the Smc machinery. Spo0J does structural and recruitment work in segregation; this is not an annotation based solely on loss-of-function necessity. Supporting Evidence: PMID:8071208 spo0J null mutants produced a significant proportion of anucleate cells during vegetative growth. PMID:31649139 A helix-turn-helix (HTH) motif in the middle domain (M) recognizes parS DNA. PMID:19450517 insertion of parS sites near the replication terminus targets SMC to this position leading to defects in chromosome organization and segregation. |
| GO:0009295 nucleoid | IEA GO_REF:0000044 | ACCEPT | Summary: Spo0J associates with the origin-proximal nucleoid/chromosome. Reason: Direct microscopy and origin-proximal binding support the localization. The broad chromosome and nucleoid terms are consistent with the more specific bacterial-nucleoid observation. Supporting Evidence: PMID:9114058 Spo0J was associated with a region of the nucleoid proximal to the cell pole, both in growing cells dividing symmetrically and in sporulating cells dividing asymmetrically. |
| GO:0030435 sporulation resulting in formation of a cellular spore | IEA GO_REF:0000043 | ACCEPT | Summary: Spo0J positively contributes to sporulation initiation through Soj-dependent regulation. Reason: The source genetic suppression experiment establishes antagonism of Soj inhibition. A regulator can participate in sporulation without executing spore structural assembly. The later Soj-DnaA-Sda mechanism refines the route to Spo0A and does not make the broad sporulation annotation non-core or false. Supporting Evidence: PMID:8071208 These results indicate that Soj inhibits the initiation of sporulation and that Spo0J antagonizes that inhibition. PMID:19450516 Spo0J performs two independent functions: regulation of initiation of DNA replication via Soj and promotion of chromosome segregation by Smc recruitment. |
| GO:0043590 bacterial nucleoid | IDA PMID:9114058 Bipolar localization of a chromosome partition protein in Ba... | ACCEPT | Summary: Spo0J associates with the origin-proximal nucleoid/chromosome. Reason: Direct microscopy and origin-proximal binding support the localization. The broad chromosome and nucleoid terms are consistent with the more specific bacterial-nucleoid observation. Supporting Evidence: PMID:9114058 Spo0J was associated with a region of the nucleoid proximal to the cell pole, both in growing cells dividing symmetrically and in sporulating cells dividing asymmetrically. |
| GO:0007059 chromosome segregation | IMP PMID:8071208 spo0J is required for normal chromosome segregation as well ... | ACCEPT | Summary: Spo0J organizes chromosomes for faithful segregation. Reason: The anucleate-cell phenotype is supplemented by direct parS DNA binding/clamp activity and recruitment of the Smc machinery. Spo0J does structural and recruitment work in segregation; this is not an annotation based solely on loss-of-function necessity. Supporting Evidence: PMID:8071208 spo0J null mutants produced a significant proportion of anucleate cells during vegetative growth. PMID:31649139 A helix-turn-helix (HTH) motif in the middle domain (M) recognizes parS DNA. PMID:19450517 insertion of parS sites near the replication terminus targets SMC to this position leading to defects in chromosome organization and segregation. |
| GO:0045881 positive regulation of sporulation resulting in formation of a cellular spore | IGI PMID:8071208 spo0J is required for normal chromosome segregation as well ... | ACCEPT | Summary: Spo0J positively contributes to sporulation initiation through Soj-dependent regulation. Reason: The source genetic suppression experiment establishes antagonism of Soj inhibition. A regulator can participate in sporulation without executing spore structural assembly. The later Soj-DnaA-Sda mechanism refines the route to Spo0A and does not make the broad sporulation annotation non-core or false. Supporting Evidence: PMID:8071208 These results indicate that Soj inhibits the initiation of sporulation and that Spo0J antagonizes that inhibition. PMID:19450516 Spo0J performs two independent functions: regulation of initiation of DNA replication via Soj and promotion of chromosome segregation by Smc recruitment. |
| GO:0043273 CTPase activity | IDA PMID:31649139 Self-organization of parS centromeres by the ParB CTP hydrol... | NEW | Summary: Purified B. subtilis Spo0J directly hydrolyzes CTP. Reason: Retain this old authored proposal with direct target IDA evidence instead of an unsubstantiated authored IBA designation. PMID:31649139 measures phosphate production, with parS stimulation and nucleotide-site mutants. Hydrolysis is distinct from ATPase activities of partner Soj/Smc and is dispensable for the DNA-loading steps tested with CTPgammaS. Supporting Evidence: PMID:31649139 ParBBsu dimers hydrolyzed about five CTP molecules per hour. PMID:31649139 The efficient stimulation of ParB-DNA entrapment by CTPΞ³S implies that CTP hydrolysis is dispensable for all steps of DNA loading. |
| GO:0002135 CTP binding | IDA PMID:31649139 Self-organization of parS centromeres by the ParB CTP hydrol... | NEW | Summary: Spo0J directly binds CTP. Reason: Retain this distinct substrate-binding proposal with direct target ITC/radiolabel evidence. R80A disrupts binding. ATP-like motif/structural resemblance alone is not decisive; the measured target substrate is CTP. Supporting Evidence: PMID:31649139 Isothermal titration calorimetry (ITC) confirmed ParBBsu binding to CTP yielding dissociation constants (Kd) in the range of 10-50 ΞΌM. |
| GO:0043221 SMC family protein binding | IPI PMID:36044845 A joint-ParB interface promotes Smc DNA recruitment. | NEW | Summary: Spo0J directly binds the Smc chromosome-organizing protein. Reason: Retain with direct target interface evidence. The crosslink and functional chimera study maps the ParB CTP-domain/Smc-joint interface, while parS-dependent SMC relocation demonstrates loader function. Engineered crosslinking/Smc ATPase-trap constructs identify contact geometry, not a native equilibrium affinity. Supporting Evidence: PMID:36044845 Using chimeric proteins and chemical cross-linking, we find that ParB directly binds the Smc subunit. PMID:19450517 insertion of parS sites near the replication terminus targets SMC to this position leading to defects in chromosome organization and segregation. |
| GO:0030174 regulation of DNA-templated DNA replication initiation | IMP PMID:18854156 Dynamic control of the DNA replication initiation protein Dn... | NEW | Summary: Spo0J regulates replication initiation through Soj. Reason: Retain the existing proposal: Spo0J modulates a regulatory protein that controls DnaA, and PMID:19450516 explicitly separates this target function from Smc recruitment. This is work in regulation, not an inference that any chromosome-segregation mutant must be a replication initiator. Keep the original authored PMID:18854156 and add the explicit target corroboration. Supporting Evidence: PMID:19450516 Spo0J performs two independent functions: regulation of initiation of DNA replication via Soj and promotion of chromosome segregation by Smc recruitment. |
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Download this section (compressed HTML)Q: Which turnover/unloading steps in native Spo0J partition complexes require CTP hydrolysis, as distinct from CTP-binding-driven loading?
Q: Which GO term best captures Spo0J-mediated SMC recruitment to bacterial parS regions, given the mitotic-spindle wording in the centromeric-region terminology?
Q: What is the detailed coupling between Spo0J clamp state, Soj regulation and the DnaA/Sda sporulation checkpoint?
Experiment: Biochemical characterization of B. subtilis Spo0J CTPase activity and kinetic parameters
Hypothesis: Spo0J hydrolyzes CTP with kinetics similar to other characterized ParB homologs
Type: enzyme kinetics assay
Experiment: ChIP-seq to map Spo0J spreading patterns from parS sites at different cell cycle stages
Hypothesis: Spo0J spreading extent varies with cell cycle stage and CTP availability
Type: ChIP-seq
Experiment: Structural analysis of Spo0J-SMC interaction interface
Hypothesis: Specific residues in the Spo0J C-terminal domain mediate SMC recruitment
Type: structural biology
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