GO_REF:0000002

Gene Ontology annotation through association of InterPro records with GO terms

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:11279056

Starvation promotes nuclear accumulation of the hsp70 Ssa4p in yeast cells.

Ssa4 accumulates reversibly in nuclei during starvation through an N-terminal targeting mechanism rather than residing constitutively in the nucleus.

"In contrast, the hsp70 Ssa4p concentrates in nuclei upon starvation. Nuclear concentration of Ssa4p in starving cells is reversible"

PMID:16429126

Proteome survey reveals modularity of the yeast cell machinery.

The study reports co-complex evidence from a genome-wide affinity-purification/mass-spectrometry survey, not a targeted binary Ssa4-Ssa2 assay.

"Here we report the first genome-wide screen for complexes in an organism, budding yeast, using affinity purification and mass spectrometry."

PMID:17892321

Structure-templated predictions of novel protein interactions from sequence information.

D-MIST predicted yeast interactions from structural motifs and sequence, with only a selected subset tested experimentally.

"A set of domains and their corresponding binding profiles were derived from extant protein structures and protein interaction data and then used to predict novel protein interactions in yeast. A number of the predicted interactions were verified experimentally"

PMID:19536198

An atlas of chaperone-protein interactions in Saccharomyces cerevisiae: implications to protein folding pathways in the cell.

The reported chaperone-chaperone associations are TAP-tag complex interactions and may be indirect.

"It should be emphasized that the interactions presented are indirect TAP-tag based interactions and not direct binary interactions."

PMID:31454312

The role of structural pleiotropy and regulatory evolution in the retention of heteromers of paralogs.

The study analyzes heteromerization among duplicated yeast homomers as an evolutionary class-level phenomenon.

"Using yeast as a model, we find that heteromerization is frequent among duplicated homomers and correlates with functional similarity between paralogs."

PMID:37968396

The social and structural architecture of the yeast protein interactome.

The reported network derives from high-throughput affinity enrichment and mass spectrometry rather than targeted binary assays for each edge.

"Here we develop a sensitive high-throughput method using highly reproducible affinity enrichment coupled to mass spectrometry combined with a quantitative two-dimensional analysis strategy to comprehensively map the interactome of Saccharomyces cerevisiae."

PMID:39456809

SSA4 Mediates Cd Tolerance via Activation of the Cis Element of VHS1 in Yeast and Enhances Cd Tolerance in Chinese Cabbage.

Under cadmium stress, Ssa4 translocates to the nucleus, associates with Pom34, regulates VHS1 expression, and reduces cadmium accumulation in yeast cells.

"ScSSA4 binds to POre Membrane 34 (POM34), a key component of nuclear pore complex (NPC), and translocates from the cytoplasm to the nucleus, where it regulates the expression of its downstream gene, Viable in a Hal3 Sit4 background 1 (VHS1), resulting in reduced Cd accumulation in yeast cells."

PMID:8754838

Functional interaction of cytosolic hsp70 and a DnaJ-related protein, Ydj1p, in protein translocation in vivo.

SSA-family Hsp70 and Ydj1 cooperate in post-translational precursor translocation, with rapid inhibition of prepro-alpha-factor import supporting a direct ER effect.

"The processing of prepro-alpha-factor was inhibited within 2 min of the shift to 37 degrees C, suggesting a direct effect of the hsp70 defect on translocation."

PMID:9789005

Folding in vivo of a newly translated yeast cytosolic enzyme is mediated by the SSA class of cytosolic yeast Hsp70 proteins.

SSA-family cytosolic Hsp70s assist ATP-dependent folding of newly translated cytosolic proteins in vivo.

"These findings indicate that, in vivo, the Hsp70 system assists in folding at least some newly translated cytosolic enzymes"

file:yeast/SSA4/SSA4-deep-research-falcon.md

Falcon deep research report on SSA4 (Saccharomyces cerevisiae, UniProt P22202, YER103W)

SSA4 (YER103W; UniProt P22202) encodes Ssa4, a stress-inducible cytosolic Hsp70 chaperone of the budding yeast Ssa subfamily (paralogs Ssa1-Ssa4) that binds non-native polypeptides and cooperates with cochaperones and quality-control systems to refold, sequester, or degrade damaged proteins.

"**SSA4 (YER103W; UniProt P22202)** encodes **Ssa4**, a **stress-inducible cytosolic Hsp70 chaperone** that supports proteostasis by binding non-native polypeptides and cooperating with cochaperones and downstream quality-control systems to refold, sequester, or degrade damaged proteins."
Ssa4 has the canonical Hsp70 two-domain architecture: an N-terminal nucleotide-binding domain (NBD) and a C-terminal substrate-binding domain (SBD) connected by a flexible linker.

"Hsp70 proteins have a canonical domain architecture consisting of an **N-terminal nucleotide-binding domain (NBD)** and a **C-terminal substrate-binding domain (SBD)** connected by a flexible linker."
Ssa4 is an ATP-dependent molecular chaperone whose substrate specificity is proteins/peptides exposing hydrophobic segments (unfolded or partially folded polypeptides), rather than a discrete small-molecule substrate.

"SSA4 encodes an **ATP-dependent molecular chaperone** (Hsp70 family) rather than an enzyme with a discrete small-molecule substrate. Its “substrate specificity” is primarily **proteins/peptides exposing hydrophobic segments**, typical of unfolded or partially folded polypeptides."
Whereas SSA1/SSA2 are constitutively expressed, SSA3/SSA4 are stress-inducible (e.g., induced during heat shock and in strains lacking SSA1/SSA2).

"- **SSA1/SSA2** are largely **constitutively expressed**. - **SSA3/SSA4** are **stress-inducible** (e.g., induced during heat shock) and can also be induced in strains lacking SSA1/SSA2."
SSA4 is a direct Hsf1 target gene and contributes to the Hsf1-Hsp70 negative feedback loop that controls heat shock response dynamics.

"- Hsf1 activates transcription of Hsp70 genes including **SSA3/SSA4**. - Hsp70 represses Hsf1, establishing a two-component negative feedback loop."
Ssa4 is consistently classified as a cytosolic/cytoplasmic Hsp70.

"In the evidence retrieved here, Ssa4 is consistently classified as a **cytosolic/cytoplasmic Hsp70** (Ssa family)."
Cytosolic Ssa Hsp70s including Ssa4 cooperate with the Hsp104 disaggregase and triage damaged proteins toward degradation (ubiquitin-proteasome system and autophagy), with stress-inducible Ssa3/Ssa4 able to reduce toxicity of aggregation-prone proteins (e.g., alpha-synuclein) by promoting autophagic clearance.

"cells expressing stress-inducible **Ssa3 or Ssa4** as the sole Ssa isoform showed reduced **α-synuclein toxicity**, and protection extended to other inclusion-forming proteins (e.g., polyQ). The mechanism supported in the excerpt is promotion of **α-synuclein degradation through autophagy**"
The Ssa family broadly supports protein folding, translocation, and degradation; yeast Ssa Hsp70 (with the Hsp40 Ydj1) mediates SRP-independent post-translational translocation of precursors into the ER and mitochondria.

"The Ssa family broadly supports folding, translocation, and degradation; depletion/inactivation causes client-folding defects, while stress-inducible **SSA3/SSA4** are induced by heat shock or **SSA1/2** loss."

file:interpro/panther/PTHR19375/PTHR19375-paint.tsv

Current PANTHER PTHR19375 PAINT annotation snapshot

PTN002500132 currently carries nucleus and cytosol IBD assertions but no plasma-membrane assertion, showing that the pinned 2025 GOA transfer is stale.

file:yeast/SSA4/SSA4-hypotheses/existing-go-0005886-keep-as-non-core/openscientist.md

OpenScientist hypothesis review of the SSA4 plasma-membrane IBA annotation

The plasma-membrane IBA lacks SSA4-specific experimental support; the available yeast plasma-membrane proteomics annotations concern other paralogs, while supported Ssa membrane-proximal roles concern ER or mitochondrial membranes rather than plasma membrane.

"The only yeast PM evidence for this family (HDA, PMID:16622836) covers the paralogs Ssa1/Ssa2/Ssb1, is contamination-prone, and **excludes Ssa4**; the genuine peripheral membrane roles of Ssa chaperones concern the **ER/mitochondrial outer membrane**, not the plasma membrane."