SSB1

Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005737 cytoplasm	IBA GO_REF:0000033	KEEP AS NON CORE	Summary: Ssb1 is cytoplasmic, but cytosol and ribosome association are more informative localizations. Reason: Correct broad localization for a cytosolic ribosome-associated Hsp70; retained as non-core because GO:0005829 is more precise. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: PANTHER:PTN002321897 · eukaryotic Hsp70 cytoplasm node SUPPORTS TRANSFER Current PTHR19375 PAINT places the broad cytoplasm IBD on PTN002321897, a eukaryotic Hsp70 node that includes Ssb-family cytosolic chaperones. SGD:S000002388 · S. cerevisiae SSB1 SUPPORTS TRANSFER The budding-yeast SSB1 self-seed records direct cytoplasmic localization evidence and is expected in its own inherited IBA. SGD:S000005153 · S. cerevisiae SSB2 SUPPORTS TRANSFER The nearly identical SSB2 paralog contributes same-organism support for cytoplasmic localization of Ssb Hsp70s. UniProtKB:P11142 · human HSPA8 SUPPORTS TRANSFER Human HSPA8 contributes metazoan support for this conserved cytoplasmic chaperone compartment.
GO:0016887 ATP hydrolysis activity	IBA GO_REF:0000033	ACCEPT	Summary: Ssb1 is a directly characterized Hsp70 ATPase. Reason: ATP hydrolysis powers the Hsp70 substrate-binding cycle and is directly supported by PMID:9860955. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000452648 · PAINT Hsp70 family node SUPPORTS TRANSFER Current PTHR19375 PAINT places the ATP hydrolysis IBD on PTN000452648, the deeply conserved Hsp70 ATPase node inherited by budding-yeast SSB1. SGD:S000002388 · S. cerevisiae SSB1 SUPPORTS TRANSFER The budding-yeast SSB1 self-seed records direct ATPase evidence for the ribosome-associated Ssb branch. UniProtKB:P0DMV8 · human HSPA1A SUPPORTS TRANSFER Human HSPA1A supports conservation of ATP hydrolysis in cytosolic Hsp70s. UniProtKB:P0A6Z1 · E. coli HscA SUPPORTS TRANSFER Bacterial HscA, a specialized Hsp70-family ATPase, anchors this activity as deeply conserved across the DnaK/Hsp70 family.
GO:0044183 protein folding chaperone	IBA GO_REF:0000033	MODIFY	Summary: Ssb1 is an ATP-dependent protein folding chaperone acting on nascent chains. Reason: The annotation is correct but GO:0140662 specifies the ATP-dependent Hsp70 mechanism more precisely. Propagation Review Root cause: TERM SCOPING PROBLEM Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN000452648 · PAINT Hsp70 family node SUPPORTS TRANSFER Current PTHR19375 PAINT places the generic chaperone IBD on PTN000452648, the family Hsp70 node inherited by SSB1. SGD:S000000905 · S. cerevisiae SSA4 SUPPORTS TRANSFER The budding-yeast Ssa-family donor supports shared ATP-dependent Hsp70 chaperone activity in cytosolic paralogs. UniProtKB:P0A6Y8 · E. coli DnaK SUPPORTS TRANSFER Bacterial DnaK contributes experimental support for folding-chaperone activity across the Hsp70/DnaK family. UniProtKB:P0DMV8 · human HSPA1A SUPPORTS TRANSFER Human HSPA1A supports conservation of the Hsp70 protein-folding chaperone cycle. Proposed replacements: ATP-dependent protein folding chaperone Supporting Evidence: PMID:28771464 The RAC heterodimer stimulates the ATPase activity of the ribosome-bound Hsp70 homolog Ssb, which interacts with nascent polypeptide chains to facilitate de novo protein folding.
GO:0005634 nucleus	IBA GO_REF:0000033	KEEP AS NON CORE	Summary: RAC-Ssb contributes to nuclear steps of ribosome biogenesis, although Ssb1 is cytosolic at steady state and actively exported. Reason: PMID:20368619 supports a nuclear RAC-Ssb role in ribosome biogenesis, while PMID:10347213 shows that Ssb1 is cytosolic at steady state; nucleus is therefore a specialized/non-core site rather than the principal localization. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: PANTHER:PTN002500132 · cytosolic/nuclear Hsp70 ancestral node SUPPORTS TRANSFER Current PTHR19375 PAINT places the nucleus IBD on PTN002500132, the opisthokont cytosolic/nuclear Hsp70 node inherited by budding-yeast SSB1. SGD:S000000004 · S. cerevisiae SSA1 SUPPORTS TRANSFER Budding-yeast SSA1 adds same-organism support for stress-linked nuclear localization of cytosolic Hsp70s. SGD:S000000905 · S. cerevisiae SSA4 SUPPORTS TRANSFER Budding-yeast SSA4 records starvation-linked nuclear localization in the same cytosolic/nuclear Hsp70 branch. UniProtKB:P11142 · human HSPA8 SUPPORTS TRANSFER Human HSPA8 contributes metazoan evidence for nuclear/nucleolar shuttling in this Hsp70 branch.
GO:0031072 heat shock protein binding	IBA GO_REF:0000033	KEEP AS NON CORE	Summary: Ssb1 engages other heat-shock proteins and cochaperones in the cytosolic chaperone network. Reason: Interactions with RAC and the Hsp110 nucleotide-exchange factor Sse1 are real, but this binding term is ancillary to Ssb1's direct folding-chaperone activity. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: PANTHER:PTN000452648 · PAINT Hsp70 family node SUPPORTS TRANSFER Current PTHR19375 PAINT places heat-shock-protein binding on PTN000452648, the family Hsp70 node inherited by SSB1. UniProtKB:P0DMV8 · human HSPA1A SUPPORTS TRANSFER Human HSPA1A supports conservation of Hsp70 interactions with cochaperones and other heat-shock proteins. UniProtKB:P0DMV9 · human HSPA1B SUPPORTS TRANSFER Human HSPA1B adds experimental support from the inducible cytosolic Hsp70 clade. UniProtKB:P11142 · human HSPA8 SUPPORTS TRANSFER Human HSPA8 supports Hsp70-network binding by a constitutive cytosolic paralog.
GO:0005829 cytosol	IBA GO_REF:0000033	ACCEPT	Summary: Cytosol is the principal compartment for Ssb1's ribosome-associated chaperone activity. Reason: Direct localization and biochemical studies place Ssb in the cytosol and on cytosolic translating ribosomes. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN002500132 · cytosolic/nuclear Hsp70 ancestral node SUPPORTS TRANSFER Current PTHR19375 PAINT places the cytosol IBD on PTN002500132, the opisthokont cytosolic/nuclear Hsp70 node inherited by budding-yeast SSB1. SGD:S000000171 · S. cerevisiae SSA3 SUPPORTS TRANSFER Budding-yeast SSA3 contributes same-organism support for cytosolic localization of cytosolic Hsp70s. SGD:S000003947 · S. cerevisiae SSA2 SUPPORTS TRANSFER Budding-yeast SSA2 adds direct support for cytosolic localization in the same opisthokont branch. UniProtKB:P11142 · human HSPA8 SUPPORTS TRANSFER Human HSPA8 contributes metazoan support for the conserved cytosolic Hsp70 compartment. Supporting Evidence: PMID:10347213 GFP-Ssb1p appeared only in the cytosol. file:yeast/SSB1/SSB1-deep-research-openscientist.md encodes Ssb1, a cytosolic, ATP-dependent molecular chaperone of the heat shock protein 70 (Hsp70) family
GO:0042026 protein refolding	IBA GO_REF:0000033	MODIFY	Summary: Current fungal PAINT has generalized this older protein-refolding assertion to protein folding. Reason: The pinned GOA row descends from PTN000452648. Current PTHR19375 PAINT explicitly places NOT/IRD for GO:0042026 at fungal node PTN001065099, sourced from PTN000452648 and dated 2026-06-16, and carries the broader GO:0006457 protein-folding assertion through that branch. Follow that node-specific generalization rather than replacing refolding with the sibling cotranslational-folding term; this does not demonstrate zero refolding capacity under every biochemical condition. Propagation Review Root cause: PROPAGATION BAD Failure modes: FUNCTIONAL DIVERGENCE Sources checked: PANTHER:PTN000452648 · PAINT Hsp70 family node SUPPORTS SOURCE BUT NOT TARGET The ancestral refolding IBD remains at PTN000452648, but descendant fungal PTN001065099 explicitly carries its NOT/IRD and generalized protein-folding assertion; the pinned leaf annotation predates this revision. Proposed replacements: protein folding Supporting Evidence: PMID:9670014 These interactions allow Ssb to function as a chaperone on the ribosome, preventing the misfolding of newly synthesized proteins.
GO:0000054 ribosomal subunit export from nucleus	IEA GO_REF:0000117	KEEP AS NON CORE	Summary: Genetic evidence links the RAC-Ssb network to ribosomal subunit maturation and export. Reason: PMID:20368619 supports an ancillary ribosome-biogenesis role; export is downstream of the core cotranslational folding activity.
GO:0005524 ATP binding	IEA GO_REF:0000002	ACCEPT	Summary: Ssb1's nucleotide-binding domain binds ATP to drive its Hsp70 cycle. Reason: ATP binding is intrinsic to the directly demonstrated ATPase-dependent chaperone mechanism.
GO:0005737 cytoplasm	IEA GO_REF:0000120	KEEP AS NON CORE	Summary: Ssb1 is cytoplasmic, but this broad localization is less informative than cytosol. Reason: Correct electronic localization; retained as non-core because cytosol and ribosome association better describe the functional pool.
GO:0006364 rRNA processing	IEA GO_REF:0000117	KEEP AS NON CORE	Summary: RAC-Ssb contributes to rRNA maturation during ribosome biogenesis. Reason: PMID:20368619 supports this genetically, but it is ancillary to Ssb1's core nascent-chain folding function.
GO:0006450 regulation of translational fidelity	IEA GO_REF:0000117	KEEP AS NON CORE	Summary: Ssb1 and RAC are required for accurate translation, especially termination. Reason: PMID:15456889 and PMID:31114879 experimentally support a genuine role in translational fidelity, but this phenotype is downstream of the core cotranslational chaperone cycle.
GO:0006452 translational frameshifting	IEA GO_REF:0000117	KEEP AS NON CORE	Summary: Loss of Ssb1/2 specifically alters programmed -1 ribosomal frameshifting. Reason: PMID:16607023 directly measured inhibition of -1, but not +1, programmed frameshifting in ssb1 ssb2 mutants; this is a genuine secondary translation phenotype rather than Ssb1's core molecular role.
GO:0016887 ATP hydrolysis activity	IEA GO_REF:0000120	ACCEPT	Summary: Ssb1 is a directly characterized Hsp70 ATPase. Reason: This electronic assertion is independently confirmed by the biochemical measurements in PMID:9860955.
GO:0051083 'de novo' cotranslational protein folding	IEA GO_REF:0000117	ACCEPT	Summary: De novo cotranslational protein folding is Ssb1's defining biological process. Reason: Ssb directly binds nascent chains at translating ribosomes, and SSB loss causes aggregation of newly synthesized proteins (PMID:9670014; PMID:23332755).
GO:0005515 protein binding	IPI PMID:11805837 Systematic identification of protein complexes in Saccharomy...	REMOVE	Summary: Generic protein binding from a large-scale affinity-purification study is not functionally informative. Reason: The interaction evidence may be valid, but the bare GO:0005515 term does not identify Ssb1's chaperone mechanism or a specific functional partner.
GO:0005515 protein binding	IPI PMID:16429126 Proteome survey reveals modularity of the yeast cell machine...	REMOVE	Summary: Generic protein binding from a proteome-wide complex survey is not functionally informative. Reason: The high-throughput interaction does not warrant retaining an unqualified protein-binding molecular function for Ssb1.
GO:0005515 protein binding	IPI PMID:16688211 Chaperone network in the yeast cytosol: Hsp110 is revealed a...	MODIFY	Summary: Sse1 binding is mechanistically relevant, but generic protein binding understates the nucleotide-exchange interaction. Reason: PMID:16688211 identifies Sse1 as an Ssb1 nucleotide-exchange factor; the bare GO:0005515 assertion should be replaced by GO:0031072 heat shock protein binding to capture the informative Hsp110/Hsp70 partner class. Proposed replacements: heat shock protein binding Supporting Evidence: PMID:16688211 the yeast homologue, Sse1p, acts as an efficient nucleotide exchange factor (NEF) for both yeast cytosolic Hsp70s, Ssa1p and Ssb1p.
GO:0005515 protein binding	IPI PMID:17559233 Proteomic analysis of in vivo 14-3-3 interactions in the yea...	REMOVE	Summary: The Ssb1-Pfk26 association was recovered in a high-throughput 14-3-3 interactome survey and does not justify generic protein binding as a useful function term. Reason: The PFK26 interaction is a co-isolated edge from the proteome-wide 14-3-3 survey in PMID:17559233; it does not establish a specific Ssb1 molecular function beyond an uninformative GO:0005515 protein-binding assertion.
GO:0005515 protein binding	IPI PMID:17612295 Yeast split-ubiquitin-based cytosolic screening system to de...	REMOVE	Summary: Generic protein binding from a split-ubiquitin interaction screen is not functionally informative. Reason: The assay identified an interaction in a screening context but does not define a specific Ssb1 molecular activity beyond generic protein binding.
GO:0005515 protein binding	IPI PMID:19387492 Yeast Uri1p promotes translation initiation and may provide ...	REMOVE	Summary: Association with the Uri1 cotranslational quality-control network is real, but generic protein binding is too broad. Reason: PMID:19387492 places Ssb1 in a chaperone network; the bare GO:0005515 row does not capture the relevant cotranslational chaperone function.
GO:0005515 protein binding	IPI PMID:37968396 The social and structural architecture of the yeast protein ...	REMOVE	Summary: Generic protein binding from a global interactome map is not functionally informative. Reason: The high-throughput interaction evidence does not define Ssb1's molecular function or a specific mechanistic binding activity beyond generic protein binding.
GO:0005737 cytoplasm	EXP PMID:10347213 A nuclear export signal prevents Saccharomyces cerevisiae Hs...	KEEP AS NON CORE	Summary: GFP-Ssb1 was cytosolic at steady state because an active nuclear export signal limits nuclear accumulation. Reason: PMID:10347213 directly supports cytoplasmic/cytosolic localization while also showing that Ssb1 can transiently shuttle through the nucleus.
GO:0005737 cytoplasm	EXP PMID:23332755 The cotranslational function of ribosome-associated Hsp70 in...	KEEP AS NON CORE	Summary: Global cotranslational profiling places Ssb on cytosolic translating ribosomes and nascent chains. Reason: PMID:23332755 directly studies the cytosolic Ssb-ribosome cycle and supports this broad cellular localization.
GO:0005886 plasma membrane	HDA PMID:16622836 The plasma membrane proteome of Saccharomyces cerevisiae and...	MARK AS OVER ANNOTATED	Summary: A bulk plasma-membrane-fraction hit is weak localization evidence for the abundant soluble cytosolic Hsp70 Ssb1. Reason: PMID:16622836 is a high-throughput survey of a stripped plasma-membrane fraction, whereas direct studies place Ssb1 in the cytosol and on cytosolic translating ribosomes. The fraction-detection annotation is retained as an experimental observation but should not be interpreted as evidence that the plasma membrane is a functional Ssb1 compartment. Supporting Evidence: PMID:16622836 Proteins from a stripped plasma membrane fraction were solubilized with the neutral and non-denaturing detergent, the n-dodecyl beta-D-maltoside.
GO:0006452 translational frameshifting	IMP PMID:16607023 Specific effects of ribosome-tethered molecular chaperones o...	KEEP AS NON CORE	Summary: Deletion of SSB1 and SSB2 specifically inhibits programmed -1 ribosomal frameshifting. Reason: PMID:16607023 directly measured a selective effect on -1 PRF, with no effect on +1 PRF; this is a secondary translational consequence of losing the ribosome-associated chaperone system.
GO:0000054 ribosomal subunit export from nucleus	IGI PMID:20368619 A ribosome-anchored chaperone network that facilitates eukar...	KEEP AS NON CORE	Summary: Genetic evidence links the Zuo1-Ssb chaperone network to ribosomal subunit maturation and export. Reason: PMID:20368619 supports this ribosome-biogenesis role, which is downstream of Ssb1's core cotranslational folding activity.
GO:0002181 cytoplasmic translation	IMP PMID:1394434 The translation machinery and 70 kd heat shock protein coope...	KEEP AS NON CORE	Summary: Ssb1/2 associate with translating ribosomes and are required for normal protein synthesis. Reason: PMID:1394434 shows slow growth, fewer translating ribosomes, and sensitivity to translation inhibitors in ssb1 ssb2 mutants. Cytoplasmic translation is the functional context for Ssb1's core nascent-chain chaperone activity, not a separate primary activity.
GO:0002181 cytoplasmic translation	IPI PMID:1394434 The translation machinery and 70 kd heat shock protein coope...	KEEP AS NON CORE	Summary: Puromycin-sensitive Ssb-ribosome association supports direct engagement of nascent chains during cytoplasmic translation. Reason: PMID:1394434 directly links Ssb1/2 to translating ribosomes and nascent-polypeptide handling, supporting translation as the context for the core folding mechanism rather than a distinct core process.
GO:0005516 calmodulin binding	IDA PMID:17146552 Identification of the divergent calmodulin binding motif in ...	KEEP AS NON CORE	Summary: Calmodulin-affinity purification and mass spectrometry identified Ssb1 as a calmodulin-binding protein. Reason: The biochemical binding evidence is direct, but PMID:17146552 did not establish a physiological consequence or a role central to Ssb1 function.
GO:0005737 cytoplasm	IDA PMID:19502427 Widespread reorganization of metabolic enzymes into reversib...	KEEP AS NON CORE	Summary: Ssb1 forms reversible cytoplasmic assemblies during nutrient starvation. Reason: PMID:19502427 supports stress-condition cytoplasmic localization, but the punctate assembly is not the core ribosome-associated state.
GO:0006364 rRNA processing	IGI PMID:20368619 A ribosome-anchored chaperone network that facilitates eukar...	KEEP AS NON CORE	Summary: The Zuo1-Ssb chaperone network contributes to maturation of 35S rRNA. Reason: PMID:20368619 supports this genetically as an ancillary ribosome-biogenesis role.
GO:0006415 translational termination	IMP PMID:17483428 Fine-tuning of translation termination efficiency in Sacchar...	KEEP AS NON CORE	Summary: SSB1 overexpression increases translation termination efficiency. Reason: PMID:17483428 identified SSB1 as one of the strongest antisuppressors in a chromosomal stop-codon readthrough screen, a genuine but downstream role relative to cotranslational folding. Supporting Evidence: PMID:17483428 Among them, SSB1 and snR18, two factors close to the exit tunnel of the ribosome, directed the strongest antisuppression effects when overexpressed, showing that they may be involved in fine-tuning of the translation termination level.
GO:0006450 regulation of translational fidelity	IMP PMID:15456889 The ribosome-bound chaperones RAC and Ssb1/2p are required f...	KEEP AS NON CORE	Summary: RAC and Ssb1/2 are required for accurate translation, with the strongest defect at termination. Reason: PMID:15456889 directly measured impaired fidelity in vivo and in vitro; PMID:31114879 later established complementary nascent-chain and ribosome-biogenesis mechanisms. This is a supported secondary consequence of RAC-Ssb function.
GO:0016887 ATP hydrolysis activity	IDA PMID:9860955 The biochemical properties of the ATPase activity of a 70-kD...	ACCEPT	Summary: Purified Ssb has directly measured ATPase activity with distinctive kinetics. Reason: PMID:9860955 reports Ssb ATP hydrolysis, including low steady-state ATP affinity, high maximal velocity, and C-terminal control of ATPase behavior.
GO:0051083 'de novo' cotranslational protein folding	IDA PMID:9670014 The molecular chaperone Ssb from Saccharomyces cerevisiae is...	ACCEPT	Summary: Ssb directly contacts nascent chains on translating ribosomes and prevents misfolding of newly synthesized proteins. Reason: PMID:9670014 provides direct puromycin-release and cross-linking evidence for Ssb as a ribosome-nascent-chain chaperone.
GO:0043022 ribosome binding	IDA PMID:9670014 The molecular chaperone Ssb from Saccharomyces cerevisiae is...	NEW	Summary: Proposed new annotation for Ssb1's directly characterized physical association with translating ribosomes. Reason: PMID:9670014 used puromycin release, salt resistance, and nascent-chain cross-linking to characterize Ssb-ribosome interaction; the current GOA set lacks a ribosome-binding molecular-function annotation. Supporting Evidence: PMID:9670014 We propose that Ssb is a core component of the translating ribosome which interacts with both the nascent polypeptide chain and the ribosome.
GO:0022626 cytosolic ribosome	IDA PMID:9670014 The molecular chaperone Ssb from Saccharomyces cerevisiae is...	NEW	Summary: Proposed new annotation for the cytosolic translating ribosome where Ssb1 performs its cotranslational chaperone cycle. Reason: PMID:9670014 directly demonstrates stable Ssb association with translating ribosomes, and PMID:1394434 identifies the SSB proteins as cytosolic Hsp70s associated with translating ribosomes. Supporting Evidence: PMID:9670014 The Ssbs of Saccharomyces cerevisiae are an abundant type of Hsp70 found associated with translating ribosomes. PMID:1394434 We suggest that cytosolic hsp70 aids in the passage of the nascent polypeptide chain through the ribosome in a manner analogous to the role played by organelle-localized hsp70 in the transport of proteins across membranes.
GO:0002181 cytoplasmic translation	IPI PMID:1394434 The translation machinery and 70 kd heat shock protein coope...	KEEP AS NON CORE	Summary: Puromycin-sensitive Ssb-ribosome association supports direct engagement of nascent chains during cytoplasmic translation. Reason: This separate IPI row carries a second SGD partner for the PMID:1394434 translation annotation. Cytoplasmic translation is the context for Ssb1's cotranslational nascent-chain folding activity rather than a distinct core process.
GO:0005515 protein binding	IPI PMID:16429126 Proteome survey reveals modularity of the yeast cell machine...	REMOVE	Summary: This separate PMID:16429126 row records a proteome-wide complex-survey interaction; generic protein binding is not functionally informative. Reason: The high-throughput interaction may be valid, but it does not warrant retaining an unqualified protein-binding molecular function for Ssb1.
GO:0005515 protein binding	IPI PMID:16429126 Proteome survey reveals modularity of the yeast cell machine...	REMOVE	Summary: This separate PMID:16429126 row records a proteome-wide complex-survey interaction; generic protein binding is not functionally informative. Reason: The high-throughput interaction may be valid, but it does not warrant retaining an unqualified protein-binding molecular function for Ssb1.

Gene Description

Existing Annotations Review

Core Functions

Ssb1 is an ATP-dependent Hsp70 folding chaperone on cytosolic translating ribosomes. RAC positions and activates Ssb1 near the 60S exit tunnel, where repeated ATP-driven binding and release cycles capture emerging nascent chains, limit their aggregation, and promote de novo cotranslational folding.

References

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SGD

SGD gene description for SSB1 (yeast)

OpenScientist

📚 Additional Documentation

Notes

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