SSA3

UniProt ID: P09435
Organism: Saccharomyces cerevisiae
Review Status: DRAFT
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Gene Description

SSA3 (YBL075C) encodes Ssa3, one of the four cytosolic Hsp70-Ssa molecular chaperones of budding yeast. It is an ATP-dependent chaperone of the Hsp70 family with an N-terminal nucleotide-binding/ATPase domain and a C-terminal substrate-binding domain that binds exposed hydrophobic segments of non-native polypeptides to prevent aggregation and promote folding/refolding and protein quality control. Unlike constitutively expressed Ssa1/Ssa2, Ssa3 and Ssa4 are stress/heat-inducible: Ssa3 has very low basal expression and is strongly induced by heat shock and other proteotoxic stress through Hsf1/heat shock element promoter architecture, and SSA3-HSE reporters are widely used as readouts of Hsf1 activity. Ssa3 functions predominantly in cytosolic and nuclear protein-homeostasis systems, works with Hsp40 co-chaperones and Hsp110 nucleotide-exchange factors, and contributes to cotranslational folding, post-translational protein translocation, refolding of denatured substrates, and prion propagation. Although the Ssa paralogs are partly redundant, Ssa3 shows measurable functional specialization. SSA3 has a paralog, SSA4, that arose from whole-genome duplication.

Existing Annotations Review

GO Term Evidence Action Reason
GO:0005634 nucleus
IBA
GO_REF:0000033 		KEEP AS NON CORE
Summary: Cytosolic Hsp70-Ssa chaperones act largely in the cytosol but the proteostasis network they support spans the cytosol and nucleus, so a nuclear pool is plausible but peripheral to the core function. Kept as non-core.
Reason: Falcon describes Ssa3 as predominantly cytosolic, functioning in the cytosol/nucleus proteostasis network. A nuclear localization is plausible but is not the primary site of action, so this is retained as a context-specific, non-core annotation.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
Predominantly cytosolic; functions in the cytosol/nucleus proteostasis network
GO:0005737 cytoplasm
IBA
GO_REF:0000033 		ACCEPT
Summary: Ssa3 is a cytosolic Hsp70; cytoplasmic localization is well supported and consistent with the UniProt subcellular location (Cytoplasm).
Reason: Falcon consistently treats SSA3 as a cytosolic Hsp70 of the Ssa family, consistent with UniProt (SUBCELLULAR LOCATION: Cytoplasm).
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
SSA3 is consistently treated as a **cytosolic** Hsp70 of the Ssa family
GO:0005886 plasma membrane
IBA
GO_REF:0000033 		KEEP AS NON CORE
Summary: Plasma membrane is not a primary site of Ssa3 action. The deep research consistently localizes Ssa3 to the cytosol; any plasma-membrane association would be transient/peripheral (e.g. via translocation or client interactions). Kept as non-core.
Reason: The falcon report describes Ssa3 as a cytosolic Hsp70 and does not support plasma membrane as a site of function. The IBA annotation is retained as a low-confidence, non-core localization rather than removed.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
SSA3 is consistently treated as a **cytosolic** Hsp70 of the Ssa family
GO:0016887 ATP hydrolysis activity
IBA
GO_REF:0000033 		ACCEPT
Summary: Ssa3 is an ATP-dependent Hsp70; ATP binding and hydrolysis by the N-terminal NBD drive the substrate-binding/release cycle. This is a core catalytic activity of the chaperone.
Reason: Falcon establishes that Hsp70/Ssa chaperones are ATP-dependent and that ATP binding and hydrolysis drive the substrate-affinity cycle, supporting ATP hydrolysis activity as a core molecular function.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
Hsp70/Ssa chaperones are **ATP-dependent**. They bind exposed hydrophobic segments of non-native proteins to prevent aggregation and promote productive folding/refolding and quality control.
file:yeast/SSA3/SSA3-deep-research-falcon.md
ATP binding and hydrolysis drive switching between low-affinity/high-exchange and high-affinity/slow-exchange substrate states; co-chaperones (notably J-domain proteins/Hsp40s) stimulate ATP hydrolysis and nucleotide-exchange factors reset the cycle.
GO:0031072 heat shock protein binding
IBA
GO_REF:0000033 		ACCEPT
Summary: Ssa3 functions within the Hsp70 chaperone network, interacting with Hsp40 (J-domain) co-chaperones and Hsp110 nucleotide-exchange factors, so heat-shock protein binding is consistent with its biology.
Reason: Falcon states that Ssa proteins function with Hsp40 J-proteins and Hsp110 NEFs, supporting heat shock protein binding.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
Ssa proteins function with Hsp40 J-proteins and Hsp110 NEFs
GO:0044183 protein folding chaperone
IBA
GO_REF:0000033 		ACCEPT
Summary: Ssa3 is a cytosolic ATP-dependent protein chaperone that assists folding and refolding and limits aggregation of non-native proteins. This is a core molecular function.
Reason: Falcon describes SSA3 as encoding a cytosolic ATP-dependent protein chaperone that assists folding/refolding and limits aggregation, supporting protein folding chaperone activity as a core function.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
SSA3 encodes a **cytosolic ATP-dependent protein chaperone** that participates in proteostasis by assisting folding/refolding and limiting aggregation of stress-denatured proteins.
GO:0005829 cytosol
IBA
GO_REF:0000033 		ACCEPT
Summary: The cytosol is the primary site of Ssa3 chaperone activity. Strongly supported and also annotated by direct assay (IDA below).
Reason: Falcon consistently treats SSA3 as a cytosolic Hsp70, supporting cytosol as the core cellular component.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
SSA3 is consistently treated as a **cytosolic** Hsp70 of the Ssa family
GO:0042026 protein refolding
IBA
GO_REF:0000033 		ACCEPT
Summary: Ssa3 promotes refolding of denatured/non-native proteins as part of the cytosolic Hsp70 system, a core biological process for a stress-inducible chaperone.
Reason: Falcon states Hsp70-Ssa proteins assist folding/refolding and that Ssa proteins promote folding, translocation, degradation, and refolding of denatured substrates, supporting protein refolding as a core process.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
Ssa proteins promote folding, translocation, degradation, and refolding of denatured substrates
GO:0000166 nucleotide binding
IEA
GO_REF:0000043 		ACCEPT
Summary: Nucleotide binding is a generic parent of the more informative ATP binding activity; Ssa3 has an N-terminal nucleotide-binding (ATPase) domain.
Reason: Consistent with the Hsp70 NBD; the more specific ATP binding (GO:0005524) is also annotated and better captures the activity.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
Hsp70 proteins consist of an N-terminal **nucleotide-binding/ATPase domain (NBD)** and a **substrate-binding domain (SBD)** with a helical
GO:0005524 ATP binding
IEA
GO_REF:0000120 		ACCEPT
Summary: Ssa3 binds ATP via its N-terminal NBD; ATP binding is required for the Hsp70 chaperone cycle. Core molecular function.
Reason: Falcon describes the N-terminal nucleotide-binding/ATPase domain and the ATP-driven substrate-affinity cycle, supporting ATP binding.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
Hsp70 proteins consist of an N-terminal **nucleotide-binding/ATPase domain (NBD)** and a **substrate-binding domain (SBD)** with a helical
GO:0005737 cytoplasm
IEA
GO_REF:0000120 		ACCEPT
Summary: Cytoplasmic localization, consistent with UniProt and with the cytosolic assignment of Ssa3. Same conclusion as the IBA cytoplasm annotation above.
Reason: Falcon treats SSA3 as a cytosolic Hsp70, consistent with cytoplasm.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
SSA3 is consistently treated as a **cytosolic** Hsp70 of the Ssa family
GO:0006457 protein folding
IEA
GO_REF:0000117 		ACCEPT
Summary: Ssa3 assists de novo and stress-induced protein folding as a cytosolic Hsp70. Core biological process. Same conclusion as the IGI protein folding annotation below.
Reason: Falcon describes Hsp70-Ssa proteins binding non-native proteins to assist folding/refolding, supporting protein folding as a core process.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
Hsp70-Ssa proteins bind exposed hydrophobic regions on unfolded proteins, assist folding/refolding, and support proteostasis
GO:0006616 SRP-dependent cotranslational protein targeting to membrane, translocation
IEA
GO_REF:0000117 		KEEP AS NON CORE
Summary: Cytosolic Hsp70-Ssa proteins assist protein translocation; an SRP-related cotranslational role is plausible but not the core function of the stress-inducible Ssa3. Kept as non-core. The exact term label (SRP-dependent) is more specific than the supporting evidence; the broader role is post-translational/translocation chaperone activity.
Reason: Falcon notes Ssa proteins promote translocation of substrates, supporting a translocation-chaperone role, but the SRP-dependent specificity is not a defining/core feature of Ssa3. Retained as non-core.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
Ssa proteins promote folding, translocation, degradation, and refolding of denatured substrates
GO:0016887 ATP hydrolysis activity
IEA
GO_REF:0000120 		ACCEPT
Summary: ATP hydrolysis by the Hsp70 NBD; core catalytic activity. Same conclusion as the IBA and IGI ATP hydrolysis annotations.
Reason: Falcon establishes ATP-dependent operation with ATP binding and hydrolysis driving the substrate-affinity cycle.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
ATP binding and hydrolysis drive switching between low-affinity/high-exchange and high-affinity/slow-exchange substrate states; co-chaperones (notably J-domain proteins/Hsp40s) stimulate ATP hydrolysis and nucleotide-exchange factors reset the cycle.
GO:0051082 unfolded protein binding
IEA
GO_REF:0000117 		MODIFY
Summary: Ssa3 binds non-native/unfolded proteins, but as an ATP-dependent Hsp70 the more precise molecular function is ATP-dependent protein folding chaperone activity (GO:0140662), which is also the term InterPro assigns in UniProt.
Reason: Falcon emphasizes that Ssa3 is an ATP-dependent chaperone whose substrate binding is coupled to the ATPase cycle; the ATP-dependent protein folding chaperone term (GO:0140662) captures this more precisely than the generic unfolded protein binding. This matches the InterPro IEA annotation in UniProt (GO:0140662).
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
ATP binding and hydrolysis drive switching between low-affinity/high-exchange and high-affinity/slow-exchange substrate states; co-chaperones (notably J-domain proteins/Hsp40s) stimulate ATP hydrolysis and nucleotide-exchange factors reset the cycle.
GO:0005515 protein binding
IPI
PMID:11805837
Systematic identification of protein complexes in Saccharomy... 		MARK AS OVER ANNOTATED
Summary: Generic protein binding from a high-throughput protein-complex mass spectrometry study; uninformative about Ssa3's molecular function, which is better captured by its chaperone/co-chaperone interaction terms.
Reason: Per curation guidance, protein binding (GO:0005515) is uninformative. More specific terms (heat shock protein binding, protein folding chaperone) capture the biology; this generic HTP annotation is over-annotated.
GO:0005515 protein binding
IPI
PMID:16554755
Global landscape of protein complexes in the yeast Saccharom... 		MARK AS OVER ANNOTATED
Summary: Generic protein binding from a high-throughput protein-complex study; uninformative about molecular function.
Reason: Protein binding (GO:0005515) is uninformative; more specific chaperone terms apply. Over-annotated.
GO:0005515 protein binding
IPI
PMID:19536198
An atlas of chaperone-protein interactions in Saccharomyces ... 		MARK AS OVER ANNOTATED
Summary: Generic protein binding from a chaperone-interaction atlas; the chaperone-substrate/co-chaperone biology is better represented by specific terms such as heat shock protein binding and protein folding chaperone.
Reason: Protein binding (GO:0005515) is uninformative. Over-annotated.
GO:0005515 protein binding
IPI
PMID:27107014
An inter-species protein-protein interaction network across ... 		MARK AS OVER ANNOTATED
Summary: Generic protein binding from an inter-species interaction network; uninformative about Ssa3's molecular function.
Reason: Protein binding (GO:0005515) is uninformative. Over-annotated.
GO:0005515 protein binding
IPI
PMID:31454312
The role of structural pleiotropy and regulatory evolution i... 		MARK AS OVER ANNOTATED
Summary: Generic protein binding from a study of paralog heteromer retention; uninformative about molecular function.
Reason: Protein binding (GO:0005515) is uninformative. Over-annotated.
GO:0006515 protein quality control for misfolded or incompletely synthesized proteins
IMP
PMID:24855027
Life-span extension by a metacaspase in the yeast Saccharomy... 		KEEP AS NON CORE
Summary: Ssa3, as a cytosolic Hsp70, contributes to protein quality control of misfolded/non-native proteins. This is a genuine part of the proteostasis role but is captured at a level peripheral to the core chaperone molecular function; kept as non-core.
Reason: Falcon supports the general role of cytosolic Hsp70-Ssa proteins in proteostasis and quality control (degradation/refolding of non-native substrates), but this term is retained as a non-core process annotation.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
Ssa proteins promote folding, translocation, degradation, and refolding of denatured substrates
GO:0005829 cytosol
IDA
PMID:10745074
Cytosolic Hsp70s are involved in the transport of aminopepti... 		ACCEPT
Summary: Direct assay localizes Ssa3 to the cytosol, the primary site of its chaperone activity. Core cellular component, also supported by phylogenetic inference (IBA cytosol above).
Reason: Direct evidence consistent with the falcon assessment of SSA3 as a cytosolic Hsp70.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
SSA3 is consistently treated as a **cytosolic** Hsp70 of the Ssa family
GO:0006457 protein folding
IGI
PMID:9789005
Folding in vivo of a newly translated yeast cytosolic enzyme... 		ACCEPT
Summary: Genetic evidence that the SSA class of cytosolic Hsp70 mediates folding in vivo of newly translated yeast proteins. Core biological process for Ssa3.
Reason: Consistent with falcon: Hsp70-Ssa proteins bind non-native proteins and assist folding; PMID:9789005 demonstrates the SSA class mediates folding of newly translated cytosolic proteins.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
Hsp70-Ssa proteins bind exposed hydrophobic regions on unfolded proteins, assist folding/refolding, and support proteostasis
GO:0006616 SRP-dependent cotranslational protein targeting to membrane, translocation
IMP
PMID:8754838
Functional interaction of cytosolic hsp70 and a DnaJ-related... 		KEEP AS NON CORE
Summary: Cytosolic Hsp70-Ssa (with the Hsp40 Ydj1) functions in protein translocation in vivo. The translocation-chaperone role is supported, but the specific SRP-dependent label is more specific than warranted as a core function of the stress-inducible Ssa3. Kept as non-core.
Reason: PMID:8754838 shows cytosolic Hsp70/Ydj1 acts in protein translocation, and falcon notes Ssa proteins promote translocation of substrates; retained as a non-core process annotation given the over-specific SRP-dependent label.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
Ssa proteins promote folding, translocation, degradation, and refolding of denatured substrates
GO:0016887 ATP hydrolysis activity
IGI
PMID:3302682
Complex interactions among members of an essential subfamily... 		ACCEPT
Summary: Genetic interactions within the essential SSA subfamily are consistent with the ATP-dependent (ATPase) Hsp70 chaperone activity. Core catalytic function; same conclusion as the other ATP hydrolysis annotations.
Reason: Falcon establishes ATP-dependent operation of the Ssa chaperones with ATP hydrolysis driving the substrate-affinity cycle.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
Hsp70/Ssa chaperones are **ATP-dependent**. They bind exposed hydrophobic segments of non-native proteins to prevent aggregation and promote productive folding/refolding and quality control.
GO:0051082 unfolded protein binding
IGI
PMID:9789005
Folding in vivo of a newly translated yeast cytosolic enzyme... 		MODIFY
Summary: Ssa3 binds non-native/unfolded proteins, but as an ATP-dependent Hsp70 the more precise molecular function is ATP-dependent protein folding chaperone activity (GO:0140662). Same conclusion as the IEA unfolded protein binding annotation above.
Reason: Falcon emphasizes ATP-dependent, ATPase-cycle-coupled substrate binding; GO:0140662 (ATP-dependent protein folding chaperone) captures this more precisely than the generic unfolded protein binding, and matches the InterPro IEA annotation in UniProt.
Supporting Evidence:
file:yeast/SSA3/SSA3-deep-research-falcon.md
ATP binding and hydrolysis drive switching between low-affinity/high-exchange and high-affinity/slow-exchange substrate states; co-chaperones (notably J-domain proteins/Hsp40s) stimulate ATP hydrolysis and nucleotide-exchange factors reset the cycle.

Core Functions

Ssa3 is a stress-inducible cytosolic Hsp70 (Ssa subfamily) that acts as an ATP-dependent protein folding chaperone: its N-terminal nucleotide-binding (ATPase) domain binds and hydrolyzes ATP to drive cycles of high- and low-affinity binding of exposed hydrophobic segments on non-native polypeptides, preventing aggregation and promoting productive folding/refolding in the cytosol.

Molecular Function:
ATP-dependent protein folding chaperone
Directly Involved In:
protein folding protein refolding
Cellular Locations:
cytosol
Supporting Evidence:
  • file:yeast/SSA3/SSA3-deep-research-falcon.md
    SSA3 encodes a **cytosolic ATP-dependent protein chaperone** that participates in proteostasis by assisting folding/refolding and limiting aggregation of stress-denatured proteins.
  • file:yeast/SSA3/SSA3-deep-research-falcon.md
    Hsp70 proteins consist of an N-terminal **nucleotide-binding/ATPase domain (NBD)** and a **substrate-binding domain (SBD)** with a helical

Ssa3 supplies stress-inducible cytosolic Hsp70 (ATP hydrolysis) capacity for the heat shock response: it has very low basal expression and is strongly, rapidly induced by heat/proteotoxic stress via Hsf1/heat shock element (HSE) promoter elements, deploying additional chaperone capacity to restore proteostasis. It functions together with Hsp40 (J-domain) co-chaperones and Hsp110 nucleotide-exchange factors.

Molecular Function:
ATP hydrolysis activity
Directly Involved In:
protein refolding
Cellular Locations:
cytosol
Supporting Evidence:
  • file:yeast/SSA3/SSA3-deep-research-falcon.md
    SSA3 has extremely low basal expression under optimal conditions but is rapidly induced by heat shock/stress
  • file:yeast/SSA3/SSA3-deep-research-falcon.md
    Ssa proteins function with Hsp40 J-proteins and Hsp110 NEFs

References

GO_REF:0000033
Annotation inferences using phylogenetic trees
GO_REF:0000043
Gene Ontology annotation based on UniProtKB/Swiss-Prot keyword mapping
GO_REF:0000117
Electronic Gene Ontology annotations created by ARBA machine learning models
GO_REF:0000120
Combined Automated Annotation using Multiple IEA Methods
PMID:10745074
Cytosolic Hsp70s are involved in the transport of aminopeptidase 1 from the cytoplasm into the vacuole.
PMID:11805837
Systematic identification of protein complexes in Saccharomyces cerevisiae by mass spectrometry.
PMID:16554755
Global landscape of protein complexes in the yeast Saccharomyces cerevisiae.
PMID:19536198
An atlas of chaperone-protein interactions in Saccharomyces cerevisiae: implications to protein folding pathways in the cell.
PMID:24855027
Life-span extension by a metacaspase in the yeast Saccharomyces cerevisiae.
PMID:27107014
An inter-species protein-protein interaction network across vast evolutionary distance.
PMID:31454312
The role of structural pleiotropy and regulatory evolution in the retention of heteromers of paralogs.
PMID:3302682
Complex interactions among members of an essential subfamily of hsp70 genes in Saccharomyces cerevisiae.
PMID:8754838
Functional interaction of cytosolic hsp70 and a DnaJ-related protein, Ydj1p, in protein translocation in vivo.
PMID:9789005
Folding in vivo of a newly translated yeast cytosolic enzyme is mediated by the SSA class of cytosolic yeast Hsp70 proteins.
file:yeast/SSA3/SSA3-deep-research-falcon.md
Falcon deep research report on SSA3
  • SSA3 encodes Ssa3, one of the four cytosolic Hsp70-Ssa proteins (Ssa1-Ssa4) in budding yeast and the stress/heat-inducible branch of the family, in contrast to the constitutively expressed Ssa1/Ssa2.
    "SSA3 is repeatedly described as a **heat/stress-inducible** cytosolic Hsp70, in contrast to **SSA1/SSA2**, which are constitutively expressed."
  • Ssa3 is a cytosolic ATP-dependent protein chaperone that assists folding/refolding and limits aggregation of stress-denatured proteins as part of the major cytosolic Hsp70 system.
    "SSA3 encodes a **cytosolic ATP-dependent protein chaperone** that participates in proteostasis by assisting folding/refolding and limiting aggregation of stress-denatured proteins."
  • Hsp70/Ssa chaperones are ATP-dependent: they bind exposed hydrophobic segments of non-native proteins to prevent aggregation and promote folding/refolding and quality control.
    "Hsp70/Ssa chaperones are **ATP-dependent**. They bind exposed hydrophobic segments of non-native proteins to prevent aggregation and promote productive folding/refolding and quality control."
  • Hsp70 architecture comprises an N-terminal nucleotide-binding/ATPase domain (NBD) and a substrate-binding domain (SBD) with a helical lid; ATP binding and hydrolysis drive switching between substrate-affinity states, with Hsp40 J-proteins stimulating ATP hydrolysis and nucleotide-exchange factors resetting the cycle.
    "ATP binding and hydrolysis drive switching between low-affinity/high-exchange and high-affinity/slow-exchange substrate states; co-chaperones (notably J-domain proteins/Hsp40s) stimulate ATP hydrolysis and nucleotide-exchange factors reset the cycle."
  • Ssa proteins function with Hsp40 (J-domain) co-chaperones and Hsp110 nucleotide-exchange factors and promote folding, translocation, degradation, and refolding of denatured substrates.
    "Ssa proteins promote folding, translocation, degradation, and refolding of denatured substrates"
  • SSA3 is a canonical Hsf1-regulated heat shock response gene with extremely low basal expression that is rapidly induced by heat shock/stress, unlike the constitutive SSA1/SSA2.
    "SSA3 has extremely low basal expression under optimal conditions but is rapidly induced by heat shock/stress"
  • SSA3 heat inducibility was mapped to two overlapping heat shock elements (HSEs) centered ~-156 bp upstream that were necessary and sufficient for heat induction; an SSA3-lacZ fusion showed very low basal activity (~4 Miller units at 23C) and strong induction within 30 minutes of heat shock.
    "A foundational promoter-dissection study mapped SSA3 heat inducibility to **two overlapping HSEs centered ~โˆ’156 bp upstream** of the transcribed region; these sequences were **necessary and sufficient** for heat induction."
  • Ssa3 is consistently treated as a cytosolic Hsp70 of the Ssa family (in contrast to compartment-specific Hsp70s such as ER BiP/Kar2), with functions in the cytosol/nucleus proteostasis network.
    "SSA3 is consistently treated as a **cytosolic** Hsp70 of the Ssa family"
  • Although the Ssa paralogs are partly redundant (yeast requires at least one Ssa for growth and paralogs can substantially compensate), Ssa3 shows measurable functional specialization, including being reported as the most proficient isoform for [PSI+] prion propagation/maintenance.
    "Ssa3 was reported as the most proficient isoform for [PSI+] propagation/maintenance"

Deep Research

Falcon

(SSA3-deep-research-falcon.md)
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 32 citations 2 artifacts 2026-05-30T17:43:54.845348
Edison artifact artifact-00 (text/markdown)
## Context ID: pqac-00000019 I have identified the requested diagrams and induction data in Figures 3 and 4. Figure 3 (from page 3) provides a diagram of the SS (image/png)

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.

Comprehensive functional annotation report: Saccharomyces cerevisiae SSA3 (UniProt P09435; locus YBL075C)

1) Gene/protein identity verification (critical disambiguation)

All evidence gathered in this report refers to the budding yeast Saccharomyces cerevisiae cytosolic Hsp70 paralog Ssa3 (gene SSA3), which is consistently discussed in the literature as one of the four cytosolic Hsp70-Ssa proteins (Ssa1โ€“Ssa4). SSA3 is repeatedly described as a heat/stress-inducible cytosolic Hsp70, in contrast to SSA1/SSA2, which are constitutively expressed. (hasin2014globaltranscriptand pages 1-2, young1993saccharomycescerevisiaehsp70 pages 1-2, hasin2014globaltranscriptand pages 2-4)

Paralog relationships reported experimentally support correct identification: Ssa1/Ssa2 are ~97% identical; the inducible isoforms Ssa3/Ssa4 are ~87โ€“88% identical to each other and share ~80% identity with Ssa1/2. (hasin2014globaltranscriptand pages 2-4)

2) Key concepts and definitions (current understanding)

2.1 What SSA3 encodes

SSA3 encodes Ssa3, a member of the Hsp70 molecular chaperone family, the major cytosolic Hsp70 system in yeast. (verghese2012biologyofthe pages 13-13, hasin2014globaltranscriptand pages 1-2)

2.2 Core Hsp70 mechanism (how Ssa3 works)

Hsp70/Ssa chaperones are ATP-dependent. They bind exposed hydrophobic segments of non-native proteins to prevent aggregation and promote productive folding/refolding and quality control. (cusack2010assessingtherole pages 30-34, hasin2014globaltranscriptand pages 1-2)

Mechanistically, Hsp70 proteins consist of an N-terminal nucleotide-binding/ATPase domain (NBD) and a substrate-binding domain (SBD) with a helical โ€œlid.โ€ ATP binding and hydrolysis drive switching between low-affinity/high-exchange and high-affinity/slow-exchange substrate states; co-chaperones (notably J-domain proteins/Hsp40s) stimulate ATP hydrolysis and nucleotide-exchange factors reset the cycle. (cusack2010assessingtherole pages 30-34, xiao2021thestudyof pages 16-20)

3) Molecular function, biological processes, and pathways

3.1 Primary function (functional annotation)

Primary molecular function: SSA3 encodes a cytosolic ATP-dependent protein chaperone that participates in proteostasis by assisting folding/refolding and limiting aggregation of stress-denatured proteins. (verghese2012biologyofthe pages 13-13, hasin2014globaltranscriptand pages 1-2)

3.2 Heat shock response (HSR) / Hsf1 regulon linkage

SSA3 is a canonical Hsf1-regulated heat shock response gene and serves as a sensitive readout of Hsf1 activity in multiple studies. The HSR is often conceptualized as a feedback system in which chaperone availability influences transcription factor activity; SSA3 is part of the induced chaperone output that helps restore proteostasis. (verghese2012biologyofthe pages 13-13, boorsteinl1990transcriptionalregulationof pages 1-2, goncalves2024cytoplasmicredoximbalance pages 10-11)

3.3 Prion propagation and protein-aggregate biology

Despite substantial redundancy among Ssa paralogs, experiments indicate Ssa3 has specialized functional effects on yeast prions, particularly the [PSI+] prion (prion form of Sup35). In systematic โ€œsingle-Ssaโ€ strains, Ssa3 was reported as the most proficient isoform for [PSI+] propagation/maintenance, while Ssa4 most strongly impaired propagation. (hasin2014globaltranscriptand pages 4-5, hasin2014globaltranscriptand pages 5-7)

4) Regulation of SSA3 expression (high-confidence primary evidence)

4.1 Basal expression and stress induction

Multiple primary studies emphasize that SSA3 has extremely low basal expression under optimal conditions but is rapidly induced by heat shock/stress, unlike SSA1/SSA2. (young1993saccharomycescerevisiaehsp70 pages 1-2, boorsteinl1990transcriptionalregulationof pages 1-2)

4.2 Promoter architecture: heat shock elements (HSEs)

A foundational promoter-dissection study mapped SSA3 heat inducibility to two overlapping HSEs centered ~โˆ’156 bp upstream of the transcribed region; these sequences were necessary and sufficient for heat induction. Removal of > half of this overlapping HSE region essentially abolished heat inducibility. (boorsteinl1990transcriptionalregulationof pages 1-2)

4.3 Quantitative induction data (classical ฮฒ-gal reporter assays)

Using an SSA3โ€“lacZ fusion, basal expression at 23ยฐC was very low (reported ~4 Miller units), and a dramatic increase was observed within 30 minutes of heat shock. A minimal โˆ’236 to โˆ’124 promoter fragment gave 2.4 Miller units basal activity and a rapid ~20-fold heat induction. (boorsteinl1990transcriptionalregulationof pages 1-2)

Experimental heat-shock conditions in the same work included growth at 23ยฐC followed by heat shock at 39ยฐC for 20 min, with multiple constructs quantified in Miller units, enabling direct comparison of HSE-containing fragments and mutant variants. (boorsteinl1990transcriptionalregulationof pages 3-4)

5) Subcellular localization

Across the sources retrieved here, SSA3 is consistently treated as a cytosolic Hsp70 of the Ssa family (in contrast to compartment-specific Hsp70s such as ER BiP/Kar2). (hasin2014globaltranscriptand pages 2-4, verghese2012biologyofthe pages 13-13, hasin2014globaltranscriptand pages 1-2)

6) Functional specialization vs redundancy among Ssa paralogs (SSA3-specific phenotypes)

A major theme is partial redundancy with measurable specialization:

  • Viability / essentiality of the Ssa system: yeast requires at least one Ssa paralog for growth; Ssa paralogs can compensate substantially for one another. (hasin2014globaltranscriptand pages 2-4, xiao2021thestudyof pages 16-20)
  • Stress inducibility: Ssa3 (with Ssa4) is inducible and expressed under non-optimal conditions; Ssa1/Ssa2 are constitutive. (hasin2014globaltranscriptand pages 2-4, boorsteinl1990transcriptionalregulationof pages 1-2)
  • Thermotolerance: In acquired thermotolerance assays, inducible isoforms (including Ssa3) showed enhanced thermotolerance relative to constitutive isoforms, and Ssa3 showed a smaller dependence on Hsp104 inhibition in at least one assay context, suggesting distinct network wiring for thermotolerance. (hasin2014globaltranscriptand pages 4-5, hasin2014globaltranscriptand pages 5-7)
  • Oxidative/cell-wall stress responses: single-Ssa strains showed differential resistance; Ssa3-expressing cells displayed greater resistance to H2O2 than Ssa1/Ssa2 in the Hasin et al. phenotyping framework. (hasin2014globaltranscriptand pages 5-7)
  • Chaperone performance readouts: Ssa1 was most efficient in one luciferase refolding assay, while Ssa3 performed comparably to Ssa1 and better than Ssa2/Ssa4 at some time points, indicating assay- and client-dependent differences among paralogs. (hasin2014globaltranscriptand pages 4-5, hasin2014globaltranscriptand pages 5-7)

7) Statistics and data highlights from experimental studies

Key quantitative/statistical points directly available from the retrieved texts include:

  • SSA3 promoter: ~4 Miller units basal at 23ยฐC; induction detected within 30 min post heat shock; minimal promoter fragment basal 2.4 Miller units with ~20-fold heat induction; heat shock performed at 39ยฐC for 20 min in the quantitative promoter study. (boorsteinl1990transcriptionalregulationof pages 1-2, boorsteinl1990transcriptionalregulationof pages 3-4)
  • Paralog abundance and similarity: Ssa2 ~4-fold more abundant than Ssa1 under optimal conditions; Ssa1/2 ~97% identical; Ssa3/4 87% identical; Ssa3/4 ~80% identical to Ssa1/2. (hasin2014globaltranscriptand pages 2-4)
  • Transcriptome reprogramming in single-Ssa strains: one report states that in the Ssa3-only strain 47 genes were induced and 79 repressed; microarray data were deposited as GEO: GSE32433. (hasin2014globaltranscriptand pages 7-9)
  • Proteostasis under redox imbalance (2024): in trr1ฮ” mutants, 20S proteasome activity was ~3-fold higher than wild type, suggesting that Hsf1/SSA3-reporter activation can occur even with elevated proteasome capacity (i.e., not necessarily due to UPS failure). (goncalves2024cytoplasmicredoximbalance pages 7-8)

8) Recent developments (prioritizing 2023โ€“2024)

8.1 SSA3 as an Hsf1/HSR reporter in contemporary mechanistic studies (2024)

A 2024 Molecular Biology of the Cell study on thioredoxin/redox imbalance explicitly used an SSA3 HSEโ€“lacZ reporter (pSSA3HSE-lacZ) to quantify Hsf1 activity and used qRT-PCR to measure SSA3 and SSA4 transcript levels (TAF10 normalization; biological and technical replication; Welchโ€™s t-tests). While the excerpted portion contains the methods rather than the numeric expression outcomes, it demonstrates that SSA3 remains a standard quantitative readout for Hsf1/HSR activation in current yeast proteostasis research. (goncalves2024cytoplasmicredoximbalance pages 10-11)

8.2 Hsf1/Hsp network engineering for biotechnology (2023)

A 2023 applied study in Biotechnology for Biofuels and Bioproducts leveraged Hsf1-dependent Hsp pathways (which include cytosolic Hsp70 genes such as SSA3) to mitigate stress from strong promoter overexpression in engineered yeast. HSF1 overexpression increased ethyl acetate production by 49.81% in one engineered background and was accompanied by elevated expression of at least some stress genes (e.g., HSP30 up 2.19-fold in the HSF1 overexpression strain). This illustrates real-world implementation of manipulating the Hsf1โ€“Hsp network that functionally contextualizes SSA3 as part of the induced chaperone arsenal. (cui2023genomewideanalysisreveals pages 11-14)

9) Current applications and real-world implementations

  • Synthetic biology/strain engineering: Recent metabolic engineering work uses the Hsf1โ€“Hsp regulon as a strategy to relieve transcriptional/proteostasis stress and improve production phenotypes; although SSA3 is not the direct engineered locus in the excerpted results, SSA-family genes are part of the canonical Hsf1-controlled stress response that is being exploited. (cui2023genomewideanalysisreveals pages 11-14)
  • Proteostasis measurement and screening: SSA3 promoter/HSE constructs (e.g., SSA3HSE-lacZ) are used as practical reporters for Hsf1 activity and cytosolic proteostasis stress in modern yeast genetics. (goncalves2024cytoplasmicredoximbalance pages 10-11)

10) Expert synthesis and interpretation (authoritative analysis anchored in evidence)

Collectively, the SSA3 literature supports a model in which SSA3 provides stress-inducible cytosolic Hsp70 capacity that is transcriptionally wired for rapid deployment under proteotoxic conditions via Hsf1/HSE promoter architecture. (verghese2012biologyofthe pages 13-13, boorsteinl1990transcriptionalregulationof pages 1-2)

While the Ssa paralogs can substitute for essential Hsp70 functions, multiple lines of evidence indicate that Ssa3 is not simply redundant: it shows distinct functional outcomes in prion propagation, thermotolerance acquisition, oxidative stress tolerance, and transcriptome remodeling when it is the sole cytosolic Ssa. This pattern is consistent with specialization emerging from fine-tuned interactions with co-chaperones/NEFs and stress-regulated expression rather than gross domain innovations. (hasin2014globaltranscriptand pages 4-5, hasin2014globaltranscriptand pages 5-7, hasin2014globaltranscriptand pages 7-9)

Visual evidence

The following figures (cropped from the primary SSA3 promoter paper) provide direct visual support for SSA3 promoter deletion mapping and quantitative heat induction (ฮฒ-galactosidase/Miller units) around the โˆ’156 HSE region: (boorsteinl1990transcriptionalregulationof media 198214a1, boorsteinl1990transcriptionalregulationof media 305408ab)

Evidence map table

The table below summarizes the major annotation aspects, key findings, and quantitative evidence:

Annotation aspect Main findings Key evidence/details Best supporting citations
Identity SSA3 is the Saccharomyces cerevisiae cytosolic Hsp70 paralog Ssa3, corresponding to the stress-inducible branch of the Ssa family Retrieved literature consistently places SSA3 among the four cytosolic Ssa Hsp70s (Ssa1โ€“Ssa4); Ssa3/Ssa4 are heat-inducible, whereas Ssa1/Ssa2 are constitutive; Ssa3/4 share 87โ€“88% identity with each other and ~80% identity with Ssa1/2; Ssa1/2 are ~97% identical (hasin2014globaltranscriptand pages 2-4, hasin2012functionalsignificanceof pages 225-229)
Molecular function ATP-dependent molecular chaperone that binds non-native polypeptides and helps prevent aggregation Hsp70-Ssa proteins bind exposed hydrophobic regions on unfolded proteins, assist folding/refolding, and support proteostasis; Ssa3 is part of the major cytosolic Hsp70 system (cusack2010assessingtherole pages 30-34, xiao2021thestudyof pages 16-20, hasin2014globaltranscriptand pages 1-2)
Mechanism Operates through the canonical Hsp70 ATPase cycle with co-chaperones and nucleotide-exchange factors Hsp70 architecture includes N-terminal ATPase/NBD, substrate-binding domain, helical lid, and C-terminal tail; ATP binding lowers substrate affinity (~10-fold higher Kd) and increases on/off rates by ~100โ€“1000-fold; Ssa proteins function with Hsp40 J-proteins and Hsp110 NEFs (verghese2012biologyofthe pages 13-13, cusack2010assessingtherole pages 30-34, xiao2021thestudyof pages 16-20)
Regulation SSA3 is strongly heat-shock inducible via Hsf1/HSE-dependent promoter elements and has little basal expression Full SSA3-lacZ fusion showed low basal activity (~4 Miller units at 23ยฐC) and strong induction within 30 min of heat shock; a 113-bp promoter fragment (-236 to -124) gave low basal activity (2.4 Miller units) and rapid ~20-fold heat induction; two overlapping HSEs centered near -156 bp were necessary/sufficient; deleting > half of the overlapping HSE abolished inducibility (boorsteinl1990transcriptionalregulationof pages 1-2)
Localization Predominantly cytosolic; functions in the cytosol/nucleus proteostasis network Ssa family is described as the major cytosolic Hsp70 system; experimental studies compare Ssa3 as a source of cytosolic Hsp70 activity in vivo (hasin2014globaltranscriptand pages 2-4, hasin2014globaltranscriptand pages 1-2)
Pathways / biological processes Core component of the heat shock response, cytosolic proteostasis, folding/refolding, and stress adaptation SSA3 is induced as part of the Hsf1-regulated heat-shock program; Ssa proteins promote folding, translocation, degradation, and refolding of denatured substrates; Ssa activity also links to translational capacity and stress survival (verghese2012biologyofthe pages 13-13, boorsteinl1990transcriptionalregulationof pages 1-2, ciccarelli2023geneticinactivationof pages 1-2)
Prion-related function Ssa3 shows specialized activity in prion biology, especially [PSI+] propagation In isoform-swap studies, Ssa3 was reported as the most proficient Ssa isoform for propagating the [PSI+] prion; Ssa-family specialization is detectable despite broad redundancy (hasin2014globaltranscriptand pages 1-2)
Paralog specialization Ssa paralogs are partly redundant but differ in stress protection and transcriptomic effects Any one Ssa isoform can support viability, but stress-inducible Ssa3/4 better support thermotolerance and some stress resistances; when Ssa3 was sole Ssa, 134 genes were induced and 120 repressed (>2-fold), supporting paralog-specific cellular programs (hasin2012functionalsignificanceof pages 267-271, verghese2012biologyofthe pages 13-13, hasin2014globaltranscriptand pages 1-2)
Quantitative data Key numeric evidence supports inducible regulation and specialization Basal SSA3-lacZ activity ~4 Miller units at 23ยฐC; minimal promoter basal 2.4 Miller units with ~20-fold heat induction; Ssa2 is ~4-fold more abundant than Ssa1 under optimal conditions; Ssa3-only cells showed 134 induced and 120 repressed genes (>2-fold) (boorsteinl1990transcriptionalregulationof pages 1-2, hasin2014globaltranscriptand pages 2-4, hasin2012functionalsignificanceof pages 267-271)
Recent developments (2023โ€“2024) Recent yeast stress studies continue to use SSA3 as a sensitive Hsf1-responsive readout of cytosolic proteostasis stress 2024 work measured SSA3/SSA4 transcript levels by qRT-PCR in redox-stressed cells and used an SSA3 HSE-lacZ reporter to quantify Hsf1 activity; in trr1ฮ” cells, 20S proteasome activity was ~3-fold higher than wild type, supporting the idea that SSA3 induction can occur alongside elevated proteasome function rather than UPS collapse (goncalves2024cytoplasmicredoximbalance pages 10-11, goncalves2024cytoplasmicredoximbalance pages 7-8)
Real-world applications SSA3/Hsf1 biology is used in yeast engineering and stress-response tuning, rather than as a direct industrial target itself Recent engineering study showed HSF1 overexpression can improve production traits: ethyl acetate increased by 49.81% in an HSF1-overexpression strain; HSP30 expression increased 2.19-fold; combined chaperone/stress-network engineering produced further gains, illustrating applied value of Hsf1โ€“Hsp70 regulon knowledge that includes SSA-family genes (cui2023genomewideanalysisreveals pages 11-14)

Table: This table compiles core functional annotation points for yeast SSA3 (UniProt P09435/YBL075C), including mechanism, regulation, localization, specialization, and recent stress-biology findings. It is useful as a concise evidence map for narrative gene annotation and citation-backed reporting.

URLs and publication dates (from retrieved sources)

  • Boorstein WR, Craig EA. โ€œTranscriptional regulation of SSA3, an HSP70 gene from Saccharomyces cerevisiae.โ€ Molecular and Cellular Biology. June 1990. https://doi.org/10.1128/mcb.10.6.3262-3267.1990 (boorsteinl1990transcriptionalregulationof pages 1-2)
  • Young MR, Craig EA. โ€œSaccharomyces cerevisiae HSP70 heat shock elements are functionally distinct.โ€ Molecular and Cellular Biology. September 1993. https://doi.org/10.1128/mcb.13.9.5637-5646.1993 (young1993saccharomycescerevisiaehsp70 pages 1-2)
  • Verghese J, Abrams J, Wang Y, Morano KA. โ€œBiology of the Heat Shock Response and Protein Chaperones: Budding Yeast as a Model System.โ€ Microbiology and Molecular Biology Reviews. June 2012. https://doi.org/10.1128/mmbr.05018-11 (verghese2012biologyofthe pages 11-12)
  • Hasin N, Cusack SA, Ali SS, Fitzpatrick DA, Jones GW. โ€œGlobal transcript and phenotypic analysis of yeast cells expressing Ssa1, Ssa2, Ssa3 or Ssa4 as sole source of cytosolic Hsp70-Ssa chaperone activity.โ€ BMC Genomics. March 2014. https://doi.org/10.1186/1471-2164-15-194 (hasin2014globaltranscriptand pages 1-2)
  • Cui D, Liu L-P, Sun L, et al. โ€œGenome-wide analysis reveals Hsf1 maintains high transcript abundanceโ€ฆ (synthetic biology application; ethyl acetate).โ€ Biotechnology for Biofuels and Bioproducts. April 2023. https://doi.org/10.1186/s13068-023-02322-2 (cui2023genomewideanalysisreveals pages 11-14)
  • Goncalves D, Duy DL, Peffer S, Morano KA. โ€œCytoplasmic redox imbalance in the thioredoxin system activates Hsf1โ€ฆโ€ Molecular Biology of the Cell. April 2024. https://doi.org/10.1091/mbc.e23-07-0296 (goncalves2024cytoplasmicredoximbalance pages 9-10)

Limitations of the current evidence set

  • The retrieved corpus does not include direct text excerpts that explicitly map SSA3 to UniProt accession P09435 or ORF YBL075C; identity confirmation is therefore based on consistent SSA3/Ssa3 usage in the yeast Hsp70-Ssa context and paralog-structure/regulation concordance. (hasin2014globaltranscriptand pages 2-4, boorsteinl1990transcriptionalregulationof pages 1-2)
  • For 2024 Goncalves et al., SSA3/SSA4 qRT-PCR outcomes are described in methods excerpts; numerical fold changes for SSA3 expression were not present in the retrieved pages. (goncalves2024cytoplasmicredoximbalance pages 10-11)

References

  1. (hasin2014globaltranscriptand pages 1-2): Naushaba Hasin, Sarah A Cusack, Shahin S Ali, David A Fitzpatrick, and Gary W Jones. Global transcript and phenotypic analysis of yeast cells expressing ssa1, ssa2, ssa3 or ssa4 as sole source of cytosolic hsp70-ssa chaperone activity. BMC Genomics, Mar 2014. URL: https://doi.org/10.1186/1471-2164-15-194, doi:10.1186/1471-2164-15-194. This article has 66 citations and is from a peer-reviewed journal.

  2. (young1993saccharomycescerevisiaehsp70 pages 1-2): Michael R. Young and Elizabeth A. Craig. Saccharomyces cerevisiae hsp70 heat shock elements are functionally distinct. Molecular and Cellular Biology, 13:5637-5646, Sep 1993. URL: https://doi.org/10.1128/mcb.13.9.5637-5646.1993, doi:10.1128/mcb.13.9.5637-5646.1993. This article has 44 citations and is from a domain leading peer-reviewed journal.

  3. (hasin2014globaltranscriptand pages 2-4): Naushaba Hasin, Sarah A Cusack, Shahin S Ali, David A Fitzpatrick, and Gary W Jones. Global transcript and phenotypic analysis of yeast cells expressing ssa1, ssa2, ssa3 or ssa4 as sole source of cytosolic hsp70-ssa chaperone activity. BMC Genomics, Mar 2014. URL: https://doi.org/10.1186/1471-2164-15-194, doi:10.1186/1471-2164-15-194. This article has 66 citations and is from a peer-reviewed journal.

  4. (verghese2012biologyofthe pages 13-13): Jacob Verghese, Jennifer Abrams, Yanyu Wang, and Kevin A. Morano. Biology of the heat shock response and protein chaperones: budding yeast (saccharomyces cerevisiae) as a model system. Microbiology and Molecular Biology Reviews, 76:115-158, Jun 2012. URL: https://doi.org/10.1128/mmbr.05018-11, doi:10.1128/mmbr.05018-11. This article has 768 citations and is from a domain leading peer-reviewed journal.

  5. (cusack2010assessingtherole pages 30-34): S Cusack. Assessing the role of hsp70 in prion propagation in saccharomyces cerevisiae. Unknown journal, 2010.

  6. (xiao2021thestudyof pages 16-20): ARC Xiao. The study of hsp70 mrna degradation mechanism in ยซsaccharomyces cerevisiaeยป. Unknown journal, 2021.

  7. (boorsteinl1990transcriptionalregulationof pages 1-2): William R. BOORSTEINl and Elizabeth A. Craig. Transcriptional regulation of ssa3, an hsp70 gene from saccharomyces cerevisiae. Molecular and Cellular Biology, 10:3262-3267, Jun 1990. URL: https://doi.org/10.1128/mcb.10.6.3262-3267.1990, doi:10.1128/mcb.10.6.3262-3267.1990. This article has 167 citations and is from a domain leading peer-reviewed journal.

  8. (goncalves2024cytoplasmicredoximbalance pages 10-11): Davi Goncalves, Duong Long Duy, Sara Peffer, and Kevin A. Morano. Cytoplasmic redox imbalance in the thioredoxin system activates hsf1 and results in hyperaccumulation of the sequestrase hsp42 with misfolded proteins. Molecular Biology of the Cell, Apr 2024. URL: https://doi.org/10.1091/mbc.e23-07-0296, doi:10.1091/mbc.e23-07-0296. This article has 4 citations and is from a domain leading peer-reviewed journal.

  9. (hasin2014globaltranscriptand pages 4-5): Naushaba Hasin, Sarah A Cusack, Shahin S Ali, David A Fitzpatrick, and Gary W Jones. Global transcript and phenotypic analysis of yeast cells expressing ssa1, ssa2, ssa3 or ssa4 as sole source of cytosolic hsp70-ssa chaperone activity. BMC Genomics, Mar 2014. URL: https://doi.org/10.1186/1471-2164-15-194, doi:10.1186/1471-2164-15-194. This article has 66 citations and is from a peer-reviewed journal.

  10. (hasin2014globaltranscriptand pages 5-7): Naushaba Hasin, Sarah A Cusack, Shahin S Ali, David A Fitzpatrick, and Gary W Jones. Global transcript and phenotypic analysis of yeast cells expressing ssa1, ssa2, ssa3 or ssa4 as sole source of cytosolic hsp70-ssa chaperone activity. BMC Genomics, Mar 2014. URL: https://doi.org/10.1186/1471-2164-15-194, doi:10.1186/1471-2164-15-194. This article has 66 citations and is from a peer-reviewed journal.

  11. (boorsteinl1990transcriptionalregulationof pages 3-4): William R. BOORSTEINl and Elizabeth A. Craig. Transcriptional regulation of ssa3, an hsp70 gene from saccharomyces cerevisiae. Molecular and Cellular Biology, 10:3262-3267, Jun 1990. URL: https://doi.org/10.1128/mcb.10.6.3262-3267.1990, doi:10.1128/mcb.10.6.3262-3267.1990. This article has 167 citations and is from a domain leading peer-reviewed journal.

  12. (hasin2014globaltranscriptand pages 7-9): Naushaba Hasin, Sarah A Cusack, Shahin S Ali, David A Fitzpatrick, and Gary W Jones. Global transcript and phenotypic analysis of yeast cells expressing ssa1, ssa2, ssa3 or ssa4 as sole source of cytosolic hsp70-ssa chaperone activity. BMC Genomics, Mar 2014. URL: https://doi.org/10.1186/1471-2164-15-194, doi:10.1186/1471-2164-15-194. This article has 66 citations and is from a peer-reviewed journal.

  13. (goncalves2024cytoplasmicredoximbalance pages 7-8): Davi Goncalves, Duong Long Duy, Sara Peffer, and Kevin A. Morano. Cytoplasmic redox imbalance in the thioredoxin system activates hsf1 and results in hyperaccumulation of the sequestrase hsp42 with misfolded proteins. Molecular Biology of the Cell, Apr 2024. URL: https://doi.org/10.1091/mbc.e23-07-0296, doi:10.1091/mbc.e23-07-0296. This article has 4 citations and is from a domain leading peer-reviewed journal.

  14. (cui2023genomewideanalysisreveals pages 11-14): Danyao Cui, Ling-Pu Liu, Lijing Sun, X. Lin, Liangcai Lin, and Cui-ying Zhang. Genome-wide analysis reveals hsf1 maintains high transcript abundance of target genes controlled by strong constitutive promoter in saccharomyces cerevisiae. Biotechnology for Biofuels and Bioproducts, Apr 2023. URL: https://doi.org/10.1186/s13068-023-02322-2, doi:10.1186/s13068-023-02322-2. This article has 8 citations and is from a domain leading peer-reviewed journal.

  15. (boorsteinl1990transcriptionalregulationof media 198214a1): William R. BOORSTEINl and Elizabeth A. Craig. Transcriptional regulation of ssa3, an hsp70 gene from saccharomyces cerevisiae. Molecular and Cellular Biology, 10:3262-3267, Jun 1990. URL: https://doi.org/10.1128/mcb.10.6.3262-3267.1990, doi:10.1128/mcb.10.6.3262-3267.1990. This article has 167 citations and is from a domain leading peer-reviewed journal.

  16. (boorsteinl1990transcriptionalregulationof media 305408ab): William R. BOORSTEINl and Elizabeth A. Craig. Transcriptional regulation of ssa3, an hsp70 gene from saccharomyces cerevisiae. Molecular and Cellular Biology, 10:3262-3267, Jun 1990. URL: https://doi.org/10.1128/mcb.10.6.3262-3267.1990, doi:10.1128/mcb.10.6.3262-3267.1990. This article has 167 citations and is from a domain leading peer-reviewed journal.

  17. (hasin2012functionalsignificanceof pages 225-229): N Hasin. Functional significance of hsp70 post-translational modification in prion propagation and cellular function. Unknown journal, 2012.

  18. (ciccarelli2023geneticinactivationof pages 1-2): Michela Ciccarelli, Anna E. Masser, Jayasankar Mohanakrishnan Kaimal, Jordi Planells, and Claes Andrรฉasson. Genetic inactivation of essential hsf1 reveals an isolated transcriptional stress response selectively induced by protein misfolding. Molecular Biology of the Cell, Sep 2023. URL: https://doi.org/10.1091/mbc.e23-05-0153, doi:10.1091/mbc.e23-05-0153. This article has 14 citations and is from a domain leading peer-reviewed journal.

  19. (hasin2012functionalsignificanceof pages 267-271): N Hasin. Functional significance of hsp70 post-translational modification in prion propagation and cellular function. Unknown journal, 2012.

  20. (verghese2012biologyofthe pages 11-12): Jacob Verghese, Jennifer Abrams, Yanyu Wang, and Kevin A. Morano. Biology of the heat shock response and protein chaperones: budding yeast (saccharomyces cerevisiae) as a model system. Microbiology and Molecular Biology Reviews, 76:115-158, Jun 2012. URL: https://doi.org/10.1128/mmbr.05018-11, doi:10.1128/mmbr.05018-11. This article has 768 citations and is from a domain leading peer-reviewed journal.

  21. (goncalves2024cytoplasmicredoximbalance pages 9-10): Davi Goncalves, Duong Long Duy, Sara Peffer, and Kevin A. Morano. Cytoplasmic redox imbalance in the thioredoxin system activates hsf1 and results in hyperaccumulation of the sequestrase hsp42 with misfolded proteins. Molecular Biology of the Cell, Apr 2024. URL: https://doi.org/10.1091/mbc.e23-07-0296, doi:10.1091/mbc.e23-07-0296. This article has 4 citations and is from a domain leading peer-reviewed journal.

Artifacts

Citations

  1. hasin2014globaltranscriptand pages 2-4
  2. boorsteinl1990transcriptionalregulationof pages 1-2
  3. boorsteinl1990transcriptionalregulationof pages 3-4
  4. hasin2014globaltranscriptand pages 5-7
  5. hasin2014globaltranscriptand pages 7-9
  6. goncalves2024cytoplasmicredoximbalance pages 7-8
  7. goncalves2024cytoplasmicredoximbalance pages 10-11
  8. cui2023genomewideanalysisreveals pages 11-14
  9. hasin2014globaltranscriptand pages 1-2
  10. verghese2012biologyofthe pages 11-12
  11. goncalves2024cytoplasmicredoximbalance pages 9-10
  12. verghese2012biologyofthe pages 13-13
  13. cusack2010assessingtherole pages 30-34
  14. xiao2021thestudyof pages 16-20
  15. hasin2014globaltranscriptand pages 4-5
  16. hasin2012functionalsignificanceof pages 225-229
  17. ciccarelli2023geneticinactivationof pages 1-2
  18. hasin2012functionalsignificanceof pages 267-271
  19. PSI+
  20. https://doi.org/10.1128/mcb.10.6.3262-3267.1990
  21. https://doi.org/10.1128/mcb.13.9.5637-5646.1993
  22. https://doi.org/10.1128/mmbr.05018-11
  23. https://doi.org/10.1186/1471-2164-15-194
  24. https://doi.org/10.1186/s13068-023-02322-2
  25. https://doi.org/10.1091/mbc.e23-07-0296
  26. https://doi.org/10.1186/1471-2164-15-194,
  27. https://doi.org/10.1128/mcb.13.9.5637-5646.1993,
  28. https://doi.org/10.1128/mmbr.05018-11,
  29. https://doi.org/10.1128/mcb.10.6.3262-3267.1990,
  30. https://doi.org/10.1091/mbc.e23-07-0296,
  31. https://doi.org/10.1186/s13068-023-02322-2,
  32. https://doi.org/10.1091/mbc.e23-05-0153,

๐Ÿ“š Additional Documentation

Notes

(SSA3-notes.md)

SSA3 review notes

Description cleanup note

The YAML description field was revised to keep it as a standalone biological summary. Project-specific curation framing moved here instead.

  • Moved out of the YAML description: wording was adjusted from cytosol/nucleus proteostasis network to avoid confusion with project-specific Proteostasis Network terminology.

๐Ÿ“„ View Raw YAML

 
id: P09435
gene_symbol: SSA3
product_type: PROTEIN
status: DRAFT
taxon:
  id: NCBITaxon:559292
  label: Saccharomyces cerevisiae
description: >-
  SSA3 (YBL075C) encodes Ssa3, one of the four cytosolic Hsp70-Ssa molecular chaperones of budding
  yeast. It is an ATP-dependent chaperone of the Hsp70 family with an N-terminal
  nucleotide-binding/ATPase domain and a C-terminal substrate-binding domain that binds exposed
  hydrophobic segments of non-native polypeptides to prevent aggregation and promote folding/refolding
  and protein quality control. Unlike constitutively expressed Ssa1/Ssa2, Ssa3 and Ssa4 are
  stress/heat-inducible: Ssa3 has very low basal expression and is strongly induced by heat shock and
  other proteotoxic stress through Hsf1/heat shock element promoter architecture, and SSA3-HSE
  reporters are widely used as readouts of Hsf1 activity. Ssa3 functions predominantly in cytosolic
  and nuclear protein-homeostasis systems, works with Hsp40 co-chaperones and Hsp110
  nucleotide-exchange factors, and contributes to cotranslational folding, post-translational protein
  translocation, refolding of denatured substrates, and prion propagation. Although the Ssa paralogs
  are partly redundant, Ssa3 shows measurable functional specialization. SSA3 has a paralog, SSA4,
  that arose from whole-genome duplication.
existing_annotations:
- term:
    id: GO:0005634
    label: nucleus
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: |-
      Cytosolic Hsp70-Ssa chaperones act largely in the cytosol but the
      proteostasis network they support spans the cytosol and nucleus, so a
      nuclear pool is plausible but peripheral to the core function. Kept as
      non-core.
    action: KEEP_AS_NON_CORE
    reason: |-
      Falcon describes Ssa3 as predominantly cytosolic, functioning in the
      cytosol/nucleus proteostasis network. A nuclear localization is plausible
      but is not the primary site of action, so this is retained as a
      context-specific, non-core annotation.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: Predominantly cytosolic; functions in the cytosol/nucleus proteostasis network
      reference_section_type: OTHER
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: |-
      Ssa3 is a cytosolic Hsp70; cytoplasmic localization is well supported and
      consistent with the UniProt subcellular location (Cytoplasm).
    action: ACCEPT
    reason: |-
      Falcon consistently treats SSA3 as a cytosolic Hsp70 of the Ssa family,
      consistent with UniProt (SUBCELLULAR LOCATION: Cytoplasm).
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: SSA3 is consistently treated as a **cytosolic** Hsp70 of the Ssa family
      reference_section_type: OTHER
- term:
    id: GO:0005886
    label: plasma membrane
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: |-
      Plasma membrane is not a primary site of Ssa3 action. The deep research
      consistently localizes Ssa3 to the cytosol; any plasma-membrane
      association would be transient/peripheral (e.g. via translocation or
      client interactions). Kept as non-core.
    action: KEEP_AS_NON_CORE
    reason: |-
      The falcon report describes Ssa3 as a cytosolic Hsp70 and does not support
      plasma membrane as a site of function. The IBA annotation is retained as a
      low-confidence, non-core localization rather than removed.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: SSA3 is consistently treated as a **cytosolic** Hsp70 of the Ssa family
      reference_section_type: OTHER
- term:
    id: GO:0016887
    label: ATP hydrolysis activity
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: |-
      Ssa3 is an ATP-dependent Hsp70; ATP binding and hydrolysis by the
      N-terminal NBD drive the substrate-binding/release cycle. This is a core
      catalytic activity of the chaperone.
    action: ACCEPT
    reason: |-
      Falcon establishes that Hsp70/Ssa chaperones are ATP-dependent and that
      ATP binding and hydrolysis drive the substrate-affinity cycle, supporting
      ATP hydrolysis activity as a core molecular function.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: |-
        Hsp70/Ssa chaperones are **ATP-dependent**. They bind exposed hydrophobic segments of non-native proteins to prevent aggregation and promote productive folding/refolding and quality control.
      reference_section_type: OTHER
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: |-
        ATP binding and hydrolysis drive switching between low-affinity/high-exchange and high-affinity/slow-exchange substrate states; co-chaperones (notably J-domain proteins/Hsp40s) stimulate ATP hydrolysis and nucleotide-exchange factors reset the cycle.
      reference_section_type: OTHER
- term:
    id: GO:0031072
    label: heat shock protein binding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: |-
      Ssa3 functions within the Hsp70 chaperone network, interacting with Hsp40
      (J-domain) co-chaperones and Hsp110 nucleotide-exchange factors, so
      heat-shock protein binding is consistent with its biology.
    action: ACCEPT
    reason: |-
      Falcon states that Ssa proteins function with Hsp40 J-proteins and Hsp110
      NEFs, supporting heat shock protein binding.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: Ssa proteins function with Hsp40 J-proteins and Hsp110 NEFs
      reference_section_type: OTHER
- term:
    id: GO:0044183
    label: protein folding chaperone
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: |-
      Ssa3 is a cytosolic ATP-dependent protein chaperone that assists folding
      and refolding and limits aggregation of non-native proteins. This is a
      core molecular function.
    action: ACCEPT
    reason: |-
      Falcon describes SSA3 as encoding a cytosolic ATP-dependent protein
      chaperone that assists folding/refolding and limits aggregation,
      supporting protein folding chaperone activity as a core function.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: |-
        SSA3 encodes a **cytosolic ATP-dependent protein chaperone** that participates in proteostasis by assisting folding/refolding and limiting aggregation of stress-denatured proteins.
      reference_section_type: OTHER
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: |-
      The cytosol is the primary site of Ssa3 chaperone activity. Strongly
      supported and also annotated by direct assay (IDA below).
    action: ACCEPT
    reason: |-
      Falcon consistently treats SSA3 as a cytosolic Hsp70, supporting cytosol
      as the core cellular component.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: SSA3 is consistently treated as a **cytosolic** Hsp70 of the Ssa family
      reference_section_type: OTHER
- term:
    id: GO:0042026
    label: protein refolding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: |-
      Ssa3 promotes refolding of denatured/non-native proteins as part of the
      cytosolic Hsp70 system, a core biological process for a stress-inducible
      chaperone.
    action: ACCEPT
    reason: |-
      Falcon states Hsp70-Ssa proteins assist folding/refolding and that Ssa
      proteins promote folding, translocation, degradation, and refolding of
      denatured substrates, supporting protein refolding as a core process.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: Ssa proteins promote folding, translocation, degradation, and refolding of denatured substrates
      reference_section_type: OTHER
- term:
    id: GO:0000166
    label: nucleotide binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000043
  review:
    summary: |-
      Nucleotide binding is a generic parent of the more informative ATP binding
      activity; Ssa3 has an N-terminal nucleotide-binding (ATPase) domain.
    action: ACCEPT
    reason: |-
      Consistent with the Hsp70 NBD; the more specific ATP binding (GO:0005524)
      is also annotated and better captures the activity.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: |-
        Hsp70 proteins consist of an N-terminal **nucleotide-binding/ATPase domain (NBD)** and a **substrate-binding domain (SBD)** with a helical
      reference_section_type: OTHER
- term:
    id: GO:0005524
    label: ATP binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: |-
      Ssa3 binds ATP via its N-terminal NBD; ATP binding is required for the
      Hsp70 chaperone cycle. Core molecular function.
    action: ACCEPT
    reason: |-
      Falcon describes the N-terminal nucleotide-binding/ATPase domain and the
      ATP-driven substrate-affinity cycle, supporting ATP binding.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: |-
        Hsp70 proteins consist of an N-terminal **nucleotide-binding/ATPase domain (NBD)** and a **substrate-binding domain (SBD)** with a helical
      reference_section_type: OTHER
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: |-
      Cytoplasmic localization, consistent with UniProt and with the cytosolic
      assignment of Ssa3. Same conclusion as the IBA cytoplasm annotation above.
    action: ACCEPT
    reason: |-
      Falcon treats SSA3 as a cytosolic Hsp70, consistent with cytoplasm.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: SSA3 is consistently treated as a **cytosolic** Hsp70 of the Ssa family
      reference_section_type: OTHER
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: |-
      Ssa3 assists de novo and stress-induced protein folding as a cytosolic
      Hsp70. Core biological process. Same conclusion as the IGI protein folding
      annotation below.
    action: ACCEPT
    reason: |-
      Falcon describes Hsp70-Ssa proteins binding non-native proteins to assist
      folding/refolding, supporting protein folding as a core process.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: Hsp70-Ssa proteins bind exposed hydrophobic regions on unfolded proteins, assist folding/refolding, and support proteostasis
      reference_section_type: OTHER
- term:
    id: GO:0006616
    label: SRP-dependent cotranslational protein targeting to membrane, translocation
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: |-
      Cytosolic Hsp70-Ssa proteins assist protein translocation; an SRP-related
      cotranslational role is plausible but not the core function of the
      stress-inducible Ssa3. Kept as non-core. The exact term label
      (SRP-dependent) is more specific than the supporting evidence; the broader
      role is post-translational/translocation chaperone activity.
    action: KEEP_AS_NON_CORE
    reason: |-
      Falcon notes Ssa proteins promote translocation of substrates, supporting
      a translocation-chaperone role, but the SRP-dependent specificity is not a
      defining/core feature of Ssa3. Retained as non-core.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: Ssa proteins promote folding, translocation, degradation, and refolding of denatured substrates
      reference_section_type: OTHER
- term:
    id: GO:0016887
    label: ATP hydrolysis activity
  evidence_type: IEA
  original_reference_id: GO_REF:0000120
  review:
    summary: |-
      ATP hydrolysis by the Hsp70 NBD; core catalytic activity. Same conclusion
      as the IBA and IGI ATP hydrolysis annotations.
    action: ACCEPT
    reason: |-
      Falcon establishes ATP-dependent operation with ATP binding and hydrolysis
      driving the substrate-affinity cycle.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: |-
        ATP binding and hydrolysis drive switching between low-affinity/high-exchange and high-affinity/slow-exchange substrate states; co-chaperones (notably J-domain proteins/Hsp40s) stimulate ATP hydrolysis and nucleotide-exchange factors reset the cycle.
      reference_section_type: OTHER
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IEA
  original_reference_id: GO_REF:0000117
  review:
    summary: |-
      Ssa3 binds non-native/unfolded proteins, but as an ATP-dependent Hsp70 the
      more precise molecular function is ATP-dependent protein folding chaperone
      activity (GO:0140662), which is also the term InterPro assigns in UniProt.
    action: MODIFY
    reason: |-
      Falcon emphasizes that Ssa3 is an ATP-dependent chaperone whose
      substrate binding is coupled to the ATPase cycle; the ATP-dependent
      protein folding chaperone term (GO:0140662) captures this more precisely
      than the generic unfolded protein binding. This matches the InterPro IEA
      annotation in UniProt (GO:0140662).
    proposed_replacement_terms:
    - id: GO:0140662
      label: ATP-dependent protein folding chaperone
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: |-
        ATP binding and hydrolysis drive switching between low-affinity/high-exchange and high-affinity/slow-exchange substrate states; co-chaperones (notably J-domain proteins/Hsp40s) stimulate ATP hydrolysis and nucleotide-exchange factors reset the cycle.
      reference_section_type: OTHER
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:11805837
  review:
    summary: |-
      Generic protein binding from a high-throughput protein-complex mass
      spectrometry study; uninformative about Ssa3's molecular function, which
      is better captured by its chaperone/co-chaperone interaction terms.
    action: MARK_AS_OVER_ANNOTATED
    reason: |-
      Per curation guidance, protein binding (GO:0005515) is uninformative.
      More specific terms (heat shock protein binding, protein folding
      chaperone) capture the biology; this generic HTP annotation is
      over-annotated.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:16554755
  review:
    summary: |-
      Generic protein binding from a high-throughput protein-complex study;
      uninformative about molecular function.
    action: MARK_AS_OVER_ANNOTATED
    reason: |-
      Protein binding (GO:0005515) is uninformative; more specific chaperone
      terms apply. Over-annotated.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:19536198
  review:
    summary: |-
      Generic protein binding from a chaperone-interaction atlas; the
      chaperone-substrate/co-chaperone biology is better represented by specific
      terms such as heat shock protein binding and protein folding chaperone.
    action: MARK_AS_OVER_ANNOTATED
    reason: |-
      Protein binding (GO:0005515) is uninformative. Over-annotated.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:27107014
  review:
    summary: |-
      Generic protein binding from an inter-species interaction network;
      uninformative about Ssa3's molecular function.
    action: MARK_AS_OVER_ANNOTATED
    reason: |-
      Protein binding (GO:0005515) is uninformative. Over-annotated.
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:31454312
  review:
    summary: |-
      Generic protein binding from a study of paralog heteromer retention;
      uninformative about molecular function.
    action: MARK_AS_OVER_ANNOTATED
    reason: |-
      Protein binding (GO:0005515) is uninformative. Over-annotated.
- term:
    id: GO:0006515
    label: protein quality control for misfolded or incompletely synthesized proteins
  evidence_type: IMP
  original_reference_id: PMID:24855027
  review:
    summary: |-
      Ssa3, as a cytosolic Hsp70, contributes to protein quality control of
      misfolded/non-native proteins. This is a genuine part of the proteostasis
      role but is captured at a level peripheral to the core chaperone
      molecular function; kept as non-core.
    action: KEEP_AS_NON_CORE
    reason: |-
      Falcon supports the general role of cytosolic Hsp70-Ssa proteins in
      proteostasis and quality control (degradation/refolding of non-native
      substrates), but this term is retained as a non-core process annotation.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: Ssa proteins promote folding, translocation, degradation, and refolding of denatured substrates
      reference_section_type: OTHER
- term:
    id: GO:0005829
    label: cytosol
  evidence_type: IDA
  original_reference_id: PMID:10745074
  review:
    summary: |-
      Direct assay localizes Ssa3 to the cytosol, the primary site of its
      chaperone activity. Core cellular component, also supported by
      phylogenetic inference (IBA cytosol above).
    action: ACCEPT
    reason: |-
      Direct evidence consistent with the falcon assessment of SSA3 as a
      cytosolic Hsp70.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: SSA3 is consistently treated as a **cytosolic** Hsp70 of the Ssa family
      reference_section_type: OTHER
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: IGI
  original_reference_id: PMID:9789005
  review:
    summary: |-
      Genetic evidence that the SSA class of cytosolic Hsp70 mediates folding in
      vivo of newly translated yeast proteins. Core biological process for Ssa3.
    action: ACCEPT
    reason: |-
      Consistent with falcon: Hsp70-Ssa proteins bind non-native proteins and
      assist folding; PMID:9789005 demonstrates the SSA class mediates folding
      of newly translated cytosolic proteins.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: Hsp70-Ssa proteins bind exposed hydrophobic regions on unfolded proteins, assist folding/refolding, and support proteostasis
      reference_section_type: OTHER
- term:
    id: GO:0006616
    label: SRP-dependent cotranslational protein targeting to membrane, translocation
  evidence_type: IMP
  original_reference_id: PMID:8754838
  review:
    summary: |-
      Cytosolic Hsp70-Ssa (with the Hsp40 Ydj1) functions in protein
      translocation in vivo. The translocation-chaperone role is supported, but
      the specific SRP-dependent label is more specific than warranted as a core
      function of the stress-inducible Ssa3. Kept as non-core.
    action: KEEP_AS_NON_CORE
    reason: |-
      PMID:8754838 shows cytosolic Hsp70/Ydj1 acts in protein translocation, and
      falcon notes Ssa proteins promote translocation of substrates; retained as
      a non-core process annotation given the over-specific SRP-dependent label.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: Ssa proteins promote folding, translocation, degradation, and refolding of denatured substrates
      reference_section_type: OTHER
- term:
    id: GO:0016887
    label: ATP hydrolysis activity
  evidence_type: IGI
  original_reference_id: PMID:3302682
  review:
    summary: |-
      Genetic interactions within the essential SSA subfamily are consistent
      with the ATP-dependent (ATPase) Hsp70 chaperone activity. Core catalytic
      function; same conclusion as the other ATP hydrolysis annotations.
    action: ACCEPT
    reason: |-
      Falcon establishes ATP-dependent operation of the Ssa chaperones with ATP
      hydrolysis driving the substrate-affinity cycle.
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: |-
        Hsp70/Ssa chaperones are **ATP-dependent**. They bind exposed hydrophobic segments of non-native proteins to prevent aggregation and promote productive folding/refolding and quality control.
      reference_section_type: OTHER
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IGI
  original_reference_id: PMID:9789005
  review:
    summary: |-
      Ssa3 binds non-native/unfolded proteins, but as an ATP-dependent Hsp70 the
      more precise molecular function is ATP-dependent protein folding chaperone
      activity (GO:0140662). Same conclusion as the IEA unfolded protein binding
      annotation above.
    action: MODIFY
    reason: |-
      Falcon emphasizes ATP-dependent, ATPase-cycle-coupled substrate binding;
      GO:0140662 (ATP-dependent protein folding chaperone) captures this more
      precisely than the generic unfolded protein binding, and matches the
      InterPro IEA annotation in UniProt.
    proposed_replacement_terms:
    - id: GO:0140662
      label: ATP-dependent protein folding chaperone
    supported_by:
    - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
      supporting_text: |-
        ATP binding and hydrolysis drive switching between low-affinity/high-exchange and high-affinity/slow-exchange substrate states; co-chaperones (notably J-domain proteins/Hsp40s) stimulate ATP hydrolysis and nucleotide-exchange factors reset the cycle.
      reference_section_type: OTHER
core_functions:
- description: |-
    Ssa3 is a stress-inducible cytosolic Hsp70 (Ssa subfamily) that acts as an
    ATP-dependent protein folding chaperone: its N-terminal nucleotide-binding
    (ATPase) domain binds and hydrolyzes ATP to drive cycles of high- and
    low-affinity binding of exposed hydrophobic segments on non-native
    polypeptides, preventing aggregation and promoting productive
    folding/refolding in the cytosol.
  molecular_function:
    id: GO:0140662
    label: ATP-dependent protein folding chaperone
  directly_involved_in:
  - id: GO:0006457
    label: protein folding
  - id: GO:0042026
    label: protein refolding
  locations:
  - id: GO:0005829
    label: cytosol
  supported_by:
  - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
    supporting_text: |-
      SSA3 encodes a **cytosolic ATP-dependent protein chaperone** that participates in proteostasis by assisting folding/refolding and limiting aggregation of stress-denatured proteins.
    reference_section_type: OTHER
  - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
    supporting_text: |-
      Hsp70 proteins consist of an N-terminal **nucleotide-binding/ATPase domain (NBD)** and a **substrate-binding domain (SBD)** with a helical
    reference_section_type: OTHER
- description: |-
    Ssa3 supplies stress-inducible cytosolic Hsp70 (ATP hydrolysis) capacity for
    the heat shock response: it has very low basal expression and is strongly,
    rapidly induced by heat/proteotoxic stress via Hsf1/heat shock element (HSE)
    promoter elements, deploying additional chaperone capacity to restore
    proteostasis. It functions together with Hsp40 (J-domain) co-chaperones and
    Hsp110 nucleotide-exchange factors.
  molecular_function:
    id: GO:0016887
    label: ATP hydrolysis activity
  directly_involved_in:
  - id: GO:0042026
    label: protein refolding
  locations:
  - id: GO:0005829
    label: cytosol
  supported_by:
  - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
    supporting_text: SSA3 has extremely low basal expression under optimal conditions but is rapidly induced by heat shock/stress
    reference_section_type: OTHER
  - reference_id: file:yeast/SSA3/SSA3-deep-research-falcon.md
    supporting_text: Ssa proteins function with Hsp40 J-proteins and Hsp110 NEFs
    reference_section_type: OTHER
references:
- 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:0000117
  title: Electronic Gene Ontology annotations created by ARBA machine learning models
  findings: []
- id: GO_REF:0000120
  title: Combined Automated Annotation using Multiple IEA Methods
  findings: []
- id: PMID:10745074
  title: Cytosolic Hsp70s are involved in the transport of aminopeptidase 1 from the cytoplasm into the vacuole.
  findings: []
- id: PMID:11805837
  title: Systematic identification of protein complexes in Saccharomyces cerevisiae by mass spectrometry.
  findings: []
- id: PMID:16554755
  title: Global landscape of protein complexes in the yeast Saccharomyces cerevisiae.
  findings: []
- id: PMID:19536198
  title: 'An atlas of chaperone-protein interactions in Saccharomyces cerevisiae: implications to protein folding pathways in the cell.'
  findings: []
- id: PMID:24855027
  title: Life-span extension by a metacaspase in the yeast Saccharomyces cerevisiae.
  findings: []
- id: PMID:27107014
  title: An inter-species protein-protein interaction network across vast evolutionary distance.
  findings: []
- id: PMID:31454312
  title: The role of structural pleiotropy and regulatory evolution in the retention of heteromers of paralogs.
  findings: []
- id: PMID:3302682
  title: Complex interactions among members of an essential subfamily of hsp70 genes in Saccharomyces cerevisiae.
  findings: []
- id: PMID:8754838
  title: Functional interaction of cytosolic hsp70 and a DnaJ-related protein, Ydj1p, in protein translocation in vivo.
  findings: []
- id: PMID:9789005
  title: Folding in vivo of a newly translated yeast cytosolic enzyme is mediated by the SSA class of cytosolic yeast Hsp70 proteins.
  findings: []
- id: file:yeast/SSA3/SSA3-deep-research-falcon.md
  title: Falcon deep research report on SSA3
  findings:
  - statement: |
      SSA3 encodes Ssa3, one of the four cytosolic Hsp70-Ssa proteins (Ssa1-Ssa4)
      in budding yeast and the stress/heat-inducible branch of the family, in
      contrast to the constitutively expressed Ssa1/Ssa2.
    supporting_text: |-
      SSA3 is repeatedly described as a **heat/stress-inducible** cytosolic Hsp70, in contrast to **SSA1/SSA2**, which are constitutively expressed.
    reference_section_type: OTHER
  - statement: |
      Ssa3 is a cytosolic ATP-dependent protein chaperone that assists
      folding/refolding and limits aggregation of stress-denatured proteins as
      part of the major cytosolic Hsp70 system.
    supporting_text: |-
      SSA3 encodes a **cytosolic ATP-dependent protein chaperone** that participates in proteostasis by assisting folding/refolding and limiting aggregation of stress-denatured proteins.
    reference_section_type: OTHER
  - statement: |
      Hsp70/Ssa chaperones are ATP-dependent: they bind exposed hydrophobic
      segments of non-native proteins to prevent aggregation and promote
      folding/refolding and quality control.
    supporting_text: |-
      Hsp70/Ssa chaperones are **ATP-dependent**. They bind exposed hydrophobic segments of non-native proteins to prevent aggregation and promote productive folding/refolding and quality control.
    reference_section_type: OTHER
  - statement: |
      Hsp70 architecture comprises an N-terminal nucleotide-binding/ATPase domain
      (NBD) and a substrate-binding domain (SBD) with a helical lid; ATP binding
      and hydrolysis drive switching between substrate-affinity states, with
      Hsp40 J-proteins stimulating ATP hydrolysis and nucleotide-exchange factors
      resetting the cycle.
    supporting_text: |-
      ATP binding and hydrolysis drive switching between low-affinity/high-exchange and high-affinity/slow-exchange substrate states; co-chaperones (notably J-domain proteins/Hsp40s) stimulate ATP hydrolysis and nucleotide-exchange factors reset the cycle.
    reference_section_type: OTHER
  - statement: |
      Ssa proteins function with Hsp40 (J-domain) co-chaperones and Hsp110
      nucleotide-exchange factors and promote folding, translocation,
      degradation, and refolding of denatured substrates.
    supporting_text: |-
      Ssa proteins promote folding, translocation, degradation, and refolding of denatured substrates
    reference_section_type: OTHER
  - statement: |
      SSA3 is a canonical Hsf1-regulated heat shock response gene with extremely
      low basal expression that is rapidly induced by heat shock/stress, unlike
      the constitutive SSA1/SSA2.
    supporting_text: |-
      SSA3 has extremely low basal expression under optimal conditions but is rapidly induced by heat shock/stress
    reference_section_type: OTHER
  - statement: |
      SSA3 heat inducibility was mapped to two overlapping heat shock elements
      (HSEs) centered ~-156 bp upstream that were necessary and sufficient for
      heat induction; an SSA3-lacZ fusion showed very low basal activity (~4
      Miller units at 23C) and strong induction within 30 minutes of heat shock.
    supporting_text: |-
      A foundational promoter-dissection study mapped SSA3 heat inducibility to **two overlapping HSEs centered ~โˆ’156 bp upstream** of the transcribed region; these sequences were **necessary and sufficient** for heat induction.
    reference_section_type: OTHER
  - statement: |
      Ssa3 is consistently treated as a cytosolic Hsp70 of the Ssa family
      (in contrast to compartment-specific Hsp70s such as ER BiP/Kar2), with
      functions in the cytosol/nucleus proteostasis network.
    supporting_text: |-
      SSA3 is consistently treated as a **cytosolic** Hsp70 of the Ssa family
    reference_section_type: OTHER
  - statement: |
      Although the Ssa paralogs are partly redundant (yeast requires at least
      one Ssa for growth and paralogs can substantially compensate), Ssa3 shows
      measurable functional specialization, including being reported as the most
      proficient isoform for [PSI+] prion propagation/maintenance.
    supporting_text: |-
      Ssa3 was reported as the most proficient isoform for [PSI+] propagation/maintenance
    reference_section_type: OTHER