Existing Annotations Review

GO Term	Evidence	Action	Reason
GO:0005789 endoplasmic reticulum membrane	IEA GO_REF:0000044	ACCEPT	Summary: UniProt subcellular-location mapping to ER membrane is consistent with direct experimental evidence that Gsf2 is an integral ER membrane protein. Reason: The ER membrane is the correct compartment for Gsf2's cargo-specific chaperone/accessory function in hexose-transporter biogenesis. Supporting Evidence: PMID:10377429 We show that gsf2 mutants accumulate Hxt1p in the endoplasmic reticulum (ER) and that Gsf2p is a 46-kDa integral membrane protein localized to the ER.
GO:0005789 endoplasmic reticulum membrane	IDA PMID:10377429 Efficient export of the glucose transporter Hxt1p from the e...	ACCEPT	Summary: Sherwood and Carlson experimentally localized Gsf2 as an integral ER membrane protein while showing that loss of GSF2 causes ER retention of Hxt1. Reason: This is direct localization evidence for the core compartment where Gsf2 acts. Supporting Evidence: PMID:10377429 We show that gsf2 mutants accumulate Hxt1p in the endoplasmic reticulum (ER) and that Gsf2p is a 46-kDa integral membrane protein localized to the ER.
GO:0005783 endoplasmic reticulum	HDA PMID:26928762 One library to make them all: streamlining the creation of y...	ACCEPT	Summary: The high-throughput ER localization is consistent with the better-supported ER membrane localization and the core ER function of Gsf2. Reason: Although broader than ER membrane, this annotation remains correct and agrees with focused localization evidence. Supporting Evidence: PMID:10377429 Gsf2p is a 46-kDa integral membrane protein localized to the ER.
GO:0005737 cytoplasm	HDA PMID:11914276 Subcellular localization of the yeast proteome	MARK AS OVER ANNOTATED	Summary: A broad cytoplasm annotation from a high-throughput localization study is not the best representation of Gsf2 biology. Focused studies and UniProt place Gsf2 in the ER membrane. Reason: Gsf2 is an ER membrane protein with a cargo-specific function in ER export and folding of membrane transporters. The cytoplasm annotation is too broad and should not be treated as a core localization. Supporting Evidence: PMID:10377429 Gsf2p is a 46-kDa integral membrane protein localized to the ER.
GO:0005741 mitochondrial outer membrane	HDA PMID:16407407 Proteomic analysis of the yeast mitochondrial outer membrane...	REMOVE	Summary: The mitochondrial outer membrane assignment is from a large-scale proteomic study and conflicts with focused experimental evidence for ER membrane localization and ER export function. Reason: No gene-specific evidence supports mitochondrial outer membrane localization for Gsf2. The experimentally supported localization is the ER membrane. Supporting Evidence: PMID:10377429 These findings suggest that Gsf2p functions in the ER to promote the secretion of certain hexose transporters.
GO:0006457 protein folding	IMP PMID:15623581 Specialized membrane-localized chaperones prevent aggregatio...	ACCEPT	Summary: Gsf2 acts as a cargo-specific membrane-localized chaperone that prevents aggregation of its cognate polytopic hexose-transporter substrates during ER membrane folding/biogenesis. Reason: PMID:15623581 directly supports a protein folding/homeostasis role for Gsf2 in the ER membrane, although the process should be interpreted as specific client maturation rather than general folding of all proteins. Supporting Evidence: PMID:15623581 Also, we show that the integral ER proteins, Gsf2p, Pho86p, and Chs7p, function similarly to Shr3p. In cells individually lacking one of these components only their cognate substrates, hexose transporters, phosphate transporters, and chitin synthase-III, respectively, aggregate and consequently fail to exit the ER membrane.
GO:0034394 protein localization to cell surface	IMP PMID:10377429 Efficient export of the glucose transporter Hxt1p from the e...	ACCEPT	Summary: Gsf2 is required for efficient ER export and plasma-membrane delivery of selected hexose transporters, especially Hxt1 and Gal2. Reason: Loss of GSF2 causes Hxt1 retention in the ER and abnormal Gal2 localization, supporting this biological-process annotation. Supporting Evidence: PMID:10377429 gsf2 mutants accumulate Hxt1p in the endoplasmic reticulum (ER) ... gsf2 mutants also display a galactose growth defect and abnormal localization of the galactose transporter Gal2p.
GO:0034394 protein localization to cell surface	IGI PMID:10377429 Efficient export of the glucose transporter Hxt1p from the e...	ACCEPT	Summary: The genetic interaction evidence with HXT1 is consistent with Gsf2's requirement for cell-surface delivery of selected hexose transporters. Reason: HXT1 was isolated as a multicopy suppressor of a gsf2 mutation, and direct localization experiments showed Hxt1 ER accumulation in gsf2 mutants. Supporting Evidence: PMID:10377429 We have isolated the HXT1 gene, which encodes a low-affinity, high-capacity glucose transporter, as a multicopy suppressor of a gsf2 mutation.
GO:0051082 unfolded protein binding	IMP PMID:15623581 Specialized membrane-localized chaperones prevent aggregatio...	MODIFY	Summary: The evidence supports a specialized membrane-protein chaperone role rather than generic unfolded protein binding. Reason: Gsf2 prevents aggregation and inappropriate interactions of cognate polytopic hexose-transporter substrates in the ER membrane. GO:0044183 protein folding chaperone captures the demonstrated client-specific chaperone function better than the broad GO:0051082 term. Proposed replacements: protein folding chaperone Supporting Evidence: PMID:15623581 These findings indicate that polytopic membrane proteins depend on specialized membrane-localized chaperones to prevent inappropriate interactions between membrane-spanning segments as they insert and fold in the lipid bilayer of the ER membrane. file:yeast/GSF2/GSF2-deep-research-falcon.md GSF2 (ECM6; YML048W) encodes an ER-localized integral membrane accessory/chaperone-like factor that promotes proper folding/assembly and efficient ER exit of a select subset of polytopic hexose transporters, with strongest evidence for Hxt1p and effects on Gal2p

Core Functions

Gsf2 is a cargo-specific ER membrane chaperone/accessory factor for selected polytopic hexose transporters. It prevents aggregation or incorrect transmembrane-segment interactions during ER membrane folding and enables efficient ER exit and cell-surface localization of clients such as Hxt1 and Gal2.

Molecular Function:

protein folding chaperone

Directly Involved In:

protein folding protein localization to cell surface

Cellular Locations:

endoplasmic reticulum membrane

Supporting Evidence:

PMID:10377429
These findings suggest that Gsf2p functions in the ER to promote the secretion of certain hexose transporters.
PMID:15623581
These findings indicate that polytopic membrane proteins depend on specialized membrane-localized chaperones to prevent inappropriate interactions between membrane-spanning segments as they insert and fold in the lipid bilayer of the ER membrane.

References

GO_REF:0000044

Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping, accompanied by conservative changes to GO terms applied by UniProt

PMID:10377429

Efficient export of the glucose transporter Hxt1p from the endoplasmic reticulum requires Gsf2p

Gsf2 is an integral ER membrane protein required for ER export of Hxt1 and normal localization of Gal2.

"We show that gsf2 mutants accumulate Hxt1p in the endoplasmic reticulum (ER) and that Gsf2p is a 46-kDa integral membrane protein localized to the ER. gsf2 mutants also display a galactose growth defect and abnormal localization of the galactose transporter Gal2p."

PMID:11914276

Subcellular localization of the yeast proteome

PMID:15623581

Specialized membrane-localized chaperones prevent aggregation of polytopic proteins in the ER

Gsf2 acts with other substrate-specific ER membrane chaperones to prevent aggregation of cognate polytopic membrane protein substrates.

"In cells individually lacking one of these components only their cognate substrates, hexose transporters, phosphate transporters, and chitin synthase-III, respectively, aggregate and consequently fail to exit the ER membrane."

PMID:16407407

Proteomic analysis of the yeast mitochondrial outer membrane reveals accumulation of a subclass of preproteins

PMID:26928762

One library to make them all: streamlining the creation of yeast libraries via a SWAp-Tag strategy

file:yeast/GSF2/GSF2-deep-research-falcon.md

Falcon deep research report for GSF2

Falcon supports GSF2 as an ER-localized, cargo-specific accessory/chaperone factor for selected hexose transporters.

"GSF2 encodes an ER-localized integral membrane accessory/chaperone-like factor that promotes proper folding/assembly and efficient ER exit of a select subset of polytopic hexose transporters, with strongest evidence for Hxt1p and effects on Gal2p."

Suggested Experiments

Experiment: Map Gsf2-client specificity using tagged Hxt1, Gal2, Hxt2, and transporter chimeras, measuring ER retention, aggregation, and plasma-membrane delivery in wild-type and gsf2 deletion cells.

Type: cell biology

Experiment: Perform crosslinking or proximity-labeling proteomics from functional tagged Gsf2 to identify direct transporter clients and ER export/quality-control partners.

Type: proteomics

Experiment: Test whether Gsf2-dependent transporter folding defects explain hydroxyurea recovery and organic-acid production phenotypes by separating transporter localization effects from downstream glucose-signaling changes.

Type: genetics

📚 Additional Documentation

Deep Research Falcon

(GSF2-deep-research-falcon.md)

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gene_id: GSF2
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gene_info: Name=GSF2; Synonyms=ECM6, EFF2; OrderedLocusNames=YML048W; ORFNames=YM9827.04;
organism_full: Saccharomyces cerevisiae (strain ATCC 204508 / S288c) (Baker's yeast).
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Question

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.

Target Gene/Protein Identity (from UniProt):

UniProt Accession: Q04697
Protein Description: RecName: Full=Glucose-signaling factor 2; AltName: Full=Extracellular mutant protein 6;
Gene Information: Name=GSF2; Synonyms=ECM6, EFF2; OrderedLocusNames=YML048W; ORFNames=YM9827.04;
Organism (full): Saccharomyces cerevisiae (strain ATCC 204508 / S288c) (Baker's yeast).
Protein Family: Not specified in UniProt
Key Domains: Gsf2. (IPR022757); Gsf2 (PF11055)

MANDATORY VERIFICATION STEPS:

Check if the gene symbol "GSF2" matches the protein description above
Verify the organism is correct: Saccharomyces cerevisiae (strain ATCC 204508 / S288c) (Baker's yeast).
Check if protein family/domains align with what you find in literature
If you find literature for a DIFFERENT gene with the same or similar symbol, STOP

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'GSF2' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information

Research Target:

Please provide a comprehensive research report on the gene GSF2 (gene ID: GSF2, UniProt: Q04697) in yeast.

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.

Output

Question: You are an expert researcher providing comprehensive, well-cited information.

Provide detailed information focusing on:
1. Key concepts and definitions with current understanding
2. Recent developments and latest research (prioritize 2023-2024 sources)
3. Current applications and real-world implementations
4. Expert opinions and analysis from authoritative sources
5. Relevant statistics and data from recent studies

Format as a comprehensive research report with proper citations. Include URLs and publication dates where available.
Always prioritize recent, authoritative sources and provide specific citations for all major claims.

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

BEFORE YOU BEGIN RESEARCH: You MUST verify you are researching the CORRECT gene/protein. Gene symbols can be ambiguous, especially for less well-characterized genes from non-model organisms.

Target Gene/Protein Identity (from UniProt):

UniProt Accession: Q04697
Protein Description: RecName: Full=Glucose-signaling factor 2; AltName: Full=Extracellular mutant protein 6;
Gene Information: Name=GSF2; Synonyms=ECM6, EFF2; OrderedLocusNames=YML048W; ORFNames=YM9827.04;
Organism (full): Saccharomyces cerevisiae (strain ATCC 204508 / S288c) (Baker's yeast).
Protein Family: Not specified in UniProt
Key Domains: Gsf2. (IPR022757); Gsf2 (PF11055)

MANDATORY VERIFICATION STEPS:

Check if the gene symbol "GSF2" matches the protein description above
Verify the organism is correct: Saccharomyces cerevisiae (strain ATCC 204508 / S288c) (Baker's yeast).
Check if protein family/domains align with what you find in literature
If you find literature for a DIFFERENT gene with the same or similar symbol, STOP

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

DO NOT PROCEED WITH RESEARCH ON A DIFFERENT GENE. Instead:
- State clearly: "The gene symbol 'GSF2' is ambiguous or literature is limited for this specific protein"
- Explain what you found (e.g., "Found extensive literature on a different gene with the same symbol in a different organism")
- Describe the protein based ONLY on the UniProt information provided above
- Suggest that the protein function can be inferred from domain/family information

Research Target:

Please provide a comprehensive research report on the gene GSF2 (gene ID: GSF2, UniProt: Q04697) in yeast.

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.

Research report: Functional annotation of Saccharomyces cerevisiae GSF2/ECM6 (UniProt Q04697; ORF YML048W)

0) Identity verification (critical disambiguation)

The literature used here consistently refers to GSF2 in Saccharomyces cerevisiae (S288c background) as also called ECM6, encoding an ER-localized integral membrane protein with a C‑terminal dilysine (KKXX) ER retrieval motif, matching the UniProt target description provided (Q04697) and ruling out confusion with similarly named genes in other organisms. (sherwood1999efficientexportof pages 1-2, sherwood1999efficientexportof pages 2-3, gancedo1998yeastcarboncatabolite pages 11-12)

1) Key concepts and definitions (current understanding)

1.1 Cargo-specific ER accessory proteins / membrane-localized chaperones

A central concept for GSF2 is that some multipass (polytopic) plasma-membrane transporters require dedicated ER-resident accessory factors for productive folding and ER exit via COPII vesicles, rather than relying only on bulk flow. Comparative discussions describe such factors as “packaging chaperones” and/or proteins that promote COPII recruitment in cargo-enriched ER regions. (gonzalez2005phosphatetransportertraffic pages 10-11, gonzalez2005phosphatetransportertraffic pages 1-2)

In yeast, Gsf2p is grouped with other cargo-specific ER membrane chaperones/accessory factors (e.g., Shr3p, Pho86p, Chs7p) that act on narrow sets of client proteins. (kota2005specializedmembranelocalizedchaperones pages 1-2, kota2005specializedmembranelocalizedchaperones pages 6-7)

1.2 Molecular role of Gsf2p (definition)

The best-supported molecular definition is:

Gsf2p is an ER-localized integral membrane accessory factor required for efficient ER exit (and proper maturation) of a subset of hexose transporters, prominently the low-affinity, high-capacity glucose transporter Hxt1p, and also impacting the galactose transporter Gal2p, while leaving other transporters (e.g., Hxt2p) largely unaffected. (sherwood1999efficientexportof pages 1-2, sherwood1999efficientexportof pages 4-5)

Mechanistically, later work supports that Gsf2p functions as a cargo-specific membrane-localized chaperone, preventing inappropriate transmembrane-segment interactions/aggregation during insertion and folding in the ER membrane. (kota2005specializedmembranelocalizedchaperones pages 6-7, kota2005specializedmembranelocalizedchaperones pages 1-2)

2) Molecular function, localization, substrates/clients, and pathway placement

2.1 Protein features and subcellular localization

Primary biochemical and microscopy evidence indicates Gsf2p is an integral membrane protein localized to the endoplasmic reticulum:

Predicted transmembrane segment (residues ~177–198) and C-terminal dilysine (KKXX) ER retrieval motif. (sherwood1999efficientexportof pages 2-3)
HA-tagged Gsf2p behaves as an integral membrane protein: found in a membrane pellet fraction and solubilized by Triton X‑100 but not by high salt. (sherwood1999efficientexportof pages 2-3)
GFP-tagged Gsf2p shows a perinuclear/ER fluorescence pattern consistent with ER localization. (sherwood1999efficientexportof pages 3-4)

2.2 Client (substrate) specificity: which transporters depend on Gsf2p?

Hxt1p (glucose transporter)
- In wild-type cells, Hxt1–GFP localizes to the plasma membrane after glucose induction; in gsf2Δ cells it shows pronounced ER accumulation, consistent with defective ER export/trafficking. (sherwood1999efficientexportof pages 3-4, sherwood1999efficientexportof media d260e999)
- HXT1 overexpression (high dosage) suppresses key gsf2 mutant phenotypes, supporting a tight functional link between Gsf2p and Hxt1p functional delivery. (sherwood1999efficientexportof pages 2-3)

Gal2p (galactose transporter)
- In gsf2Δ cells, Gal2–GFP shows aberrant punctate cytoplasmic localization rather than typical plasma membrane localization, and gsf2Δ causes a galactose growth defect (more evident at lower temperature). (sherwood1999efficientexportof pages 4-5, sherwood1999efficientexportof media 5ce4fc75)

Hxt2p (glucose transporter)
- Hxt2p localization/function is reported as largely normal in gsf2Δ strains, indicating that Gsf2p is not a universal secretory factor but has cargo selectivity among hexose transporters. (sherwood1999efficientexportof pages 4-5, sherwood1999efficientexportof pages 5-6)

2.3 Mechanism: ER export vs. membrane chaperone model

Sherwood & Carlson (1999) framed Gsf2p as an ER factor required for efficient export of Hxt1p from the ER, discussing analogies to other ER membrane proteins implicated in selective cargo export. (sherwood1999efficientexportof pages 4-5)

Kota & Ljungdahl (2005) strengthened the mechanistic model by providing evidence consistent with a membrane-localized chaperone role: in gsf2 mutants, Hxt1p exhibits enhanced cross-linking/aggregation behavior, while unrelated membrane proteins (e.g., Sec61p) do not, supporting the idea that Gsf2p prevents inappropriate interactions/aggregation of its cognate substrate(s) during ER biogenesis. (kota2005specializedmembranelocalizedchaperones pages 6-7)

2.4 Connection to glucose signaling / carbon catabolite repression (CCR)

Historically, GSF2 was identified genetically through glucose signaling phenotypes: mutations in GSF1/GSF2 relieve glucose repression of genes such as SUC2 and GAL10. (gancedo1998yeastcarboncatabolite pages 11-12)

Sherwood & Carlson interpreted this as an indirect consequence of altered transporter delivery—i.e., reduced functional glucose transport at the plasma membrane can mimic glucose starvation conditions, affecting CCR and explaining synthetic interactions with the Snf1 pathway. (sherwood1999efficientexportof pages 4-5)

3) Recent developments (prioritizing 2023–2024)

3.1 2024 functional genomics: replication stress recovery / hydroxyurea resistance

A 2024 genome-wide conditional degron resource and screening study identified GSF2 as a hydroxyurea (HU) resistance factor:

Screen found 93 HU-resistance candidate genes using a cutoff of CGI ≤ −0.2 and adjusted P < 0.05; GSF2 was among HU-specific hits. (gameiro2024genomewideconditionaldegron pages 5-6)
Validation: a GSF2-AID* strain showed HU sensitivity specifically when the degron system was induced (5‑Ph‑IAA), consistent with an on-target requirement for Gsf2p. (gameiro2024genomewideconditionaldegron pages 5-6)
Notably, a public deletion-collection gsf2Δ strain did not show HU sensitivity, while a clean gsf2Δ derived from sporulation did, highlighting how background mutations can mask phenotypes in longstanding resources. (gameiro2024genomewideconditionaldegron pages 5-6)

Interpretation: This extends GSF2 biology beyond sugar transporter trafficking per se, suggesting ER trafficking capacity or membrane-protein homeostasis may influence recovery from replication stress (mechanism not yet resolved in the excerpt). (gameiro2024genomewideconditionaldegron pages 5-6)

3.2 2024 metabolic engineering: organic-acid production (3‑HP)

A 2024 Nature Communications metabolic engineering study on 3‑hydroxypropionic acid (3‑HP) production reports GSF2 deletion (gsf2Δ) as a strategy that “could significantly improve” 3‑HP production, motivated by prior evidence that GSF2 deletion can shift metabolism toward respiration and improve ATP supply—an important constraint for organic-acid export/proton pumping. (qin2024increasedco2fixation pages 6-7)

Although the excerpt does not provide an isolated effect size for gsf2Δ alone, the paper reports the overall engineered system improved 3‑HP from 0.14 g/L to 11.25 g/L in shake flasks with 20 g/L glucose. (qin2024increasedco2fixation pages 6-7)

4) Current applications and real-world implementations

4.1 Strain engineering to alleviate glucose repression and improve organic-acid fermentation

Baek et al. (2016) demonstrated an applied use-case for gsf2 loss-of-function in engineered yeast producing D-lactic acid:

Parental strain (JHY5210): 28.9 g/L glucose consumed; 16.9 g/L D‑LA produced; yield 0.58 g/g.
Evolved strain (JHY5310): 49.3 g/L glucose; 36.8 g/L D‑LA; yield 0.75 g/g.
Engineered gsf2Δ strain (JHY5212): 45.8 g/L glucose; 33.2 g/L D‑LA (close to evolved performance). (baek2016gsf2deletionincreases pages 2-3)

This is interpreted as improved ATP and redox (NAD+) balance through increased respiratory flux when glucose repression is alleviated. (baek2016gsf2deletionincreases pages 1-2, baek2016gsf2deletionincreases pages 6-7)

Because Gsf2p affects delivery of certain hexose transporters (Hxt1; Gal2), altering GSF2 can be used as a non-obvious metabolic control knob that works “upstream” at the level of transporter biogenesis/trafficking rather than enzyme kinetics. (sherwood1999efficientexportof pages 1-2, baek2016gsf2deletionincreases pages 2-3)

4.2 Stress tolerance phenotypes used for functional screening

A yeast functional study on DMSO detoxification/tolerance found that GSF2 deletion confers tolerance to 8% DMSO in plate-based spot assays, placing GSF2 among trafficking/sorting-related genes affecting chemical stress response. (zhang2013thetranscriptionalcontrol pages 16-16)

5) Expert opinions / authoritative synthesis (interpretive analysis)

5.1 Why a trafficking factor appears as a “glucose signaling” gene

Older authoritative CCR review literature could place GSF2 upstream of Snf1 with unknown mechanism. (gancedo1998yeastcarboncatabolite pages 11-12)

The later mechanistic interpretation supported by trafficking studies is that “glucose signaling” phenotypes may arise because GSF2 controls the effective abundance/localization of specific hexose transporters at the plasma membrane, thereby modulating glucose uptake and intracellular signaling states (glucose limitation vs abundance). (sherwood1999efficientexportof pages 4-5, sherwood1999efficientexportof pages 1-2)

5.2 Where in the cell Gsf2p acts and what it is not

The strongest evidence supports an ER-localized function (not plasma-membrane transport itself) and a role in protein biogenesis/quality control/ER export rather than enzymatic catalysis. (sherwood1999efficientexportof pages 2-3, kota2005specializedmembranelocalizedchaperones pages 6-7)

6) Relevant statistics and data highlights (selected)

Reporter activity: HXT1::lacZ and HXT3::lacZ expressed in wild-type and gsf2 mutants, reported as 154 ± 5 and 337 ± 26 β-gal units (supports post-transcriptional defect model for transporter localization). (sherwood1999efficientexportof pages 2-3)
Physiology (gsf2Δ effect on fluxes): specific glucose consumption rate reduced 26% (to 5.31 ± 0.07 from 7.22 ± 0.51 mmol·h−1·g−1) and ethanol production rate reduced 24% (to 10.01 ± 0.11 from 13.11 ± 0.72 mmol·h−1·g−1), with modest reduction in growth rate (μ 0.462 ± 0.004 h−1 vs 0.485 ± 0.010 h−1). (baek2016gsf2deletionincreases pages 3-5)
Replication stress screen: 93 HU resistance candidate genes at CGI ≤ −0.2 and adjusted P < 0.05; GSF2 validated via conditional degradation and clean deletion. (gameiro2024genomewideconditionaldegron pages 5-6)
Chemical tolerance assay: gsf2Δ tolerance tested at 8% DMSO. (zhang2013thetranscriptionalcontrol pages 16-16)

7) Visual evidence (primary paper figures)

Microscopy panels from Sherwood & Carlson (1999) show the core trafficking phenotype: Hxt1–GFP ER accumulation and Gal2–GFP mislocalization in gsf2Δ compared with wild-type, supporting the ER-export/maturation model. (sherwood1999efficientexportof media d260e999, sherwood1999efficientexportof media 5ce4fc75)

8) Summary functional annotation (most defensible statement)

GSF2 (ECM6; YML048W) encodes an ER-localized integral membrane accessory/chaperone-like factor that promotes proper folding/assembly and efficient ER exit of a select subset of polytopic hexose transporters, with strongest evidence for Hxt1p and effects on Gal2p, thereby indirectly influencing glucose uptake, glucose repression (CCR) outputs, and broader physiological traits relevant to stress tolerance and industrial organic-acid production. (sherwood1999efficientexportof pages 1-2, kota2005specializedmembranelocalizedchaperones pages 6-7, baek2016gsf2deletionincreases pages 2-3)

Evidence summary table

Evidence type	Key finding (function/localization/pathway)	Specific experimental evidence or quantitative data	Publication (authors, year)	Publication date	URL/DOI
Primary	GSF2/ECM6 encodes an ER-localized integral membrane factor required for efficient ER export of selected hexose transporters, especially Hxt1; also affects Gal2 but not Hxt2, linking transporter trafficking to glucose signaling/glucose repression.	Gsf2p is a ~46-kDa integral membrane protein with a predicted TM segment (aa 177–198) and C-terminal dilysine ER-retrieval motif; HA-Gsf2p found in the 13,000 × g membrane pellet and solubilized by Triton X-100 but not 1 M NaCl. HXT1 overexpression suppressed gsf2-related phenotypes. HXT1::lacZ and HXT3::lacZ expression remained detectable in gsf2 mutants (154 ± 5 and 337 ± 26 β-gal units), arguing against a primary transcription defect. Hxt1–GFP localized to the plasma membrane in WT by 90 min after 4% glucose induction but accumulated in the ER in gsf2Δ cells; Gal2–GFP showed punctate cytoplasmic mislocalization in gsf2Δ; no maltose growth defect observed at 24°C or 30°C. Initial suppressor screen surveyed ~43,000 colonies and yielded 34 5-FOA-resistant candidates (6 Raf1 His1, 28 Raf2 His2). (sherwood1999efficientexportof pages 1-2, sherwood1999efficientexportof pages 2-3, sherwood1999efficientexportof pages 4-5, sherwood1999efficientexportof pages 3-4, sherwood1999efficientexportof pages 5-6, sherwood1999efficientexportof media d260e999)	Sherwood & Carlson, 1999	Jun 1999	https://doi.org/10.1073/pnas.96.13.7415
Primary / mechanistic	Gsf2p functions as a cargo-specific membrane-localized ER chaperone/accessory factor that prevents aggregation/misfolding of its cognate polytopic substrates (hexose transporters), enabling ER exit.	In gsf2 mutant cells, Hxt1p showed enhanced chemical cross-linking/aggregation behavior, whereas unrelated membrane proteins such as Gap1p and Sec61p did not show the same effect. Authors describe the phenotype as an “almost all-or-nothing” substrate-specific aggregation phenomenon and group Gsf2p with Shr3p-, Pho86p-, and Chs7p-like accessory proteins whose loss causes ER retention of cognate cargos. (kota2005specializedmembranelocalizedchaperones pages 6-7, kota2005specializedmembranelocalizedchaperones pages 1-2, kota2005specializedmembranelocalizedchaperones pages 5-6, kota2005specializedmembranelocalizedchaperones pages 7-8)	Kota & Ljungdahl, 2005	Jan 2005	https://doi.org/10.1083/jcb.200408106
Review	GSF2 is placed in the glucose signaling/carbon catabolite repression network as a factor whose mutation relieves glucose repression of SUC2 and GAL10; mechanism was unresolved in the pre-trafficking-era review literature.	Review notes that mutations in GSF1 and GSF2 relieve glucose repression of SUC2 and GAL10 and suggests GSF1, and possibly GSF2, act upstream of Snf1. It also notes GSF2 encodes a protein with a hydrophobic stretch and a C-terminal dilysine motif consistent with ER retention/retrieval. (gancedo1998yeastcarboncatabolite pages 11-12)	Gancedo, 1998	Jun 1998	https://doi.org/10.1128/mmbr.62.2.334-361.1998
Biotech / primary	Deletion of GSF2 alleviates glucose repression and improves D-lactic acid tolerance/production in engineered yeast, likely by reducing effective hexose transporter delivery and shifting metabolism toward respiration.	In the engineered D-LA system, parental strain JHY5210 consumed 28.9 g/L glucose and produced 16.9 g/L D-LA (yield 0.58 g/g), whereas evolved strain JHY5310 consumed 49.3 g/L and produced 36.8 g/L D-LA (yield 0.75 g/g). Constructed gsf2Δ strain JHY5212 consumed 45.8 g/L glucose and produced 33.2 g/L D-LA. In another background, gsf2Δ reduced specific glucose consumption rate by 26% (to 5.31 ± 0.07 from 7.22 ± 0.51 mmol·h−1·g−1) and specific ethanol production rate by 24% (to 10.01 ± 0.11 from 13.11 ± 0.72 mmol·h−1·g−1), while specific growth rate fell modestly from 0.485 ± 0.010 to 0.462 ± 0.004 h−1. Respiratory genes COX6, NDI1, SDH1 and glucose-repressed SUC2 were derepressed. (baek2016gsf2deletionincreases pages 6-7, baek2016gsf2deletionincreases pages 1-2, baek2016gsf2deletionincreases pages 3-5, baek2016gsf2deletionincreases pages 2-3)	Baek et al., 2016	Oct 2016	https://doi.org/10.1038/srep34812
Functional genomics / stress phenotype	GSF2 deletion confers tolerance to high DMSO; annotation supports ER-localized integral membrane protein status and implicates trafficking/cell-stress pathways.	In spot assays on YPD plus 8% DMSO, GSF2 deletion scored as DMSO tolerant (“++”). Experimental setup used 10-fold serial dilutions and 5 days incubation at 30°C. Table annotation describes GSF2 as “ER localized integ[ral membrane protein].” (zhang2013thetranscriptionalcontrol pages 16-16)	Zhang et al., 2013	Mar 2013	https://doi.org/10.1111/1567-1364.12022
Biotech / metabolic engineering	GSF2 deletion was used as a rational engineering lever to improve 3-hydroxypropionic acid (3-HP) production, based on prior evidence that it relieves Crabtree-associated glucose repression and increases respiratory ATP supply.	Qin et al. state that deletion of GSF2 could significantly improve 3-HP production and include gsf2Δ among tested engineering combinations. The paper’s overall engineered system improved 3-HP from 0.14 g/L to 11.25 g/L in shake flasks with 20 g/L glucose, though the excerpt does not assign a standalone numeric titer increase specifically to gsf2Δ. Mechanistic justification is ATP demand for organic-acid export/proton pumping and the expectation that greater respiratory flux improves ATP availability. (qin2024increasedco2fixation pages 6-7)	Qin et al., 2024	Feb 2024	https://doi.org/10.1038/s41467-024-45557-9
Functional genomics / recent development	Recent conditional-degron screens identify GSF2 as a hydroxyurea-resistance factor, expanding its phenotype space beyond transporter trafficking into replication-stress recovery.	Genome-wide AID screens identified 93 HU-resistance candidate genes using CGI ≤ −0.2 and adjusted P < 0.05; GSF2 was among HU-specific hits. A GSF2-AID* allele showed hydroxyurea sensitivity only upon auxin analog (5-Ph-IAA) treatment. A clean gsf2Δ strain generated by sporulation phenocopied HU sensitivity, whereas the public deletion-collection strain did not, implying background suppressors. Cell-cycle analysis indicated normal early S-phase arrest in HU but delayed recovery after release. (gameiro2024genomewideconditionaldegron pages 5-6)	Gameiro et al., 2024	Dec 2024	https://doi.org/10.1083/jcb.202409007
Concept / comparative trafficking biology	Gsf2p is cited as a paradigm of cargo-specific ER exit/accessory factors for membrane transporters; conceptually analogous to plant PHF1 and yeast PHO86/SHR3/ERV14 systems.	Comparative discussion argues that specific membrane cargos often require dedicated ER accessory proteins that either act as “packaging chaperones” or recruit COPII machinery to cargo-enriched ER domains. GSF2 is listed among known accessory proteins required for ER exit of specific hexose transporters, emphasizing the broader principle that these factors are structurally diverse but functionally converge on cargo-selective ER export. (gonzalez2005phosphatetransportertraffic pages 10-11, gonzalez2005phosphatetransportertraffic pages 1-2)	Gonzalez et al., 2005	Nov 2005	https://doi.org/10.1105/tpc.105.036640

Table: This table compiles key primary, review, functional-genomics, and biotechnology evidence for Saccharomyces cerevisiae GSF2/ECM6. It highlights the gene’s established ER trafficking role, substrate specificity, pathway context, and recent applied and systems-level findings.

References

(sherwood1999efficientexportof pages 1-2): Peter W. Sherwood and Marian Carlson. Efficient export of the glucose transporter hxt1p from the endoplasmic reticulum requires gsf2p. Proceedings of the National Academy of Sciences of the United States of America, 96 13:7415-20, Jun 1999. URL: https://doi.org/10.1073/pnas.96.13.7415, doi:10.1073/pnas.96.13.7415. This article has 65 citations and is from a highest quality peer-reviewed journal.
(sherwood1999efficientexportof pages 2-3): Peter W. Sherwood and Marian Carlson. Efficient export of the glucose transporter hxt1p from the endoplasmic reticulum requires gsf2p. Proceedings of the National Academy of Sciences of the United States of America, 96 13:7415-20, Jun 1999. URL: https://doi.org/10.1073/pnas.96.13.7415, doi:10.1073/pnas.96.13.7415. This article has 65 citations and is from a highest quality peer-reviewed journal.
(gancedo1998yeastcarboncatabolite pages 11-12): Juana M. Gancedo. Yeast carbon catabolite repression. Microbiology and Molecular Biology Reviews, 62:334-361, Jun 1998. URL: https://doi.org/10.1128/mmbr.62.2.334-361.1998, doi:10.1128/mmbr.62.2.334-361.1998. This article has 1719 citations and is from a domain leading peer-reviewed journal.
(gonzalez2005phosphatetransportertraffic pages 10-11): Esperanza González, Roberto Solano, Vicente Rubio, Antonio Leyva, and Javier Paz-Ares. Phosphate transporter traffic facilitator1 is a plant-specific sec12-related protein that enables the endoplasmic reticulum exit of a high-affinity phosphate transporter in arabidopsis [w]. The Plant Cell, 17:3500-3512, Nov 2005. URL: https://doi.org/10.1105/tpc.105.036640, doi:10.1105/tpc.105.036640. This article has 415 citations.
(gonzalez2005phosphatetransportertraffic pages 1-2): Esperanza González, Roberto Solano, Vicente Rubio, Antonio Leyva, and Javier Paz-Ares. Phosphate transporter traffic facilitator1 is a plant-specific sec12-related protein that enables the endoplasmic reticulum exit of a high-affinity phosphate transporter in arabidopsis [w]. The Plant Cell, 17:3500-3512, Nov 2005. URL: https://doi.org/10.1105/tpc.105.036640, doi:10.1105/tpc.105.036640. This article has 415 citations.
(kota2005specializedmembranelocalizedchaperones pages 1-2): Jhansi Kota and Per O. Ljungdahl. Specialized membrane-localized chaperones prevent aggregation of polytopic proteins in the er. The Journal of Cell Biology, 168:79-88, Jan 2005. URL: https://doi.org/10.1083/jcb.200408106, doi:10.1083/jcb.200408106. This article has 134 citations.
(kota2005specializedmembranelocalizedchaperones pages 6-7): Jhansi Kota and Per O. Ljungdahl. Specialized membrane-localized chaperones prevent aggregation of polytopic proteins in the er. The Journal of Cell Biology, 168:79-88, Jan 2005. URL: https://doi.org/10.1083/jcb.200408106, doi:10.1083/jcb.200408106. This article has 134 citations.
(sherwood1999efficientexportof pages 4-5): Peter W. Sherwood and Marian Carlson. Efficient export of the glucose transporter hxt1p from the endoplasmic reticulum requires gsf2p. Proceedings of the National Academy of Sciences of the United States of America, 96 13:7415-20, Jun 1999. URL: https://doi.org/10.1073/pnas.96.13.7415, doi:10.1073/pnas.96.13.7415. This article has 65 citations and is from a highest quality peer-reviewed journal.
(sherwood1999efficientexportof pages 3-4): Peter W. Sherwood and Marian Carlson. Efficient export of the glucose transporter hxt1p from the endoplasmic reticulum requires gsf2p. Proceedings of the National Academy of Sciences of the United States of America, 96 13:7415-20, Jun 1999. URL: https://doi.org/10.1073/pnas.96.13.7415, doi:10.1073/pnas.96.13.7415. This article has 65 citations and is from a highest quality peer-reviewed journal.
(sherwood1999efficientexportof media d260e999): Peter W. Sherwood and Marian Carlson. Efficient export of the glucose transporter hxt1p from the endoplasmic reticulum requires gsf2p. Proceedings of the National Academy of Sciences of the United States of America, 96 13:7415-20, Jun 1999. URL: https://doi.org/10.1073/pnas.96.13.7415, doi:10.1073/pnas.96.13.7415. This article has 65 citations and is from a highest quality peer-reviewed journal.
(sherwood1999efficientexportof media 5ce4fc75): Peter W. Sherwood and Marian Carlson. Efficient export of the glucose transporter hxt1p from the endoplasmic reticulum requires gsf2p. Proceedings of the National Academy of Sciences of the United States of America, 96 13:7415-20, Jun 1999. URL: https://doi.org/10.1073/pnas.96.13.7415, doi:10.1073/pnas.96.13.7415. This article has 65 citations and is from a highest quality peer-reviewed journal.
(sherwood1999efficientexportof pages 5-6): Peter W. Sherwood and Marian Carlson. Efficient export of the glucose transporter hxt1p from the endoplasmic reticulum requires gsf2p. Proceedings of the National Academy of Sciences of the United States of America, 96 13:7415-20, Jun 1999. URL: https://doi.org/10.1073/pnas.96.13.7415, doi:10.1073/pnas.96.13.7415. This article has 65 citations and is from a highest quality peer-reviewed journal.
(gameiro2024genomewideconditionaldegron pages 5-6): Eduardo Gameiro, Karla A. Juárez-Núñez, Jia Jun Fung, Susmitha Shankar, Brian Luke, and Anton Khmelinskii. Genome-wide conditional degron libraries for functional genomics. Journal of Cell Biology, Dec 2024. URL: https://doi.org/10.1083/jcb.202409007, doi:10.1083/jcb.202409007. This article has 13 citations and is from a highest quality peer-reviewed journal.
(qin2024increasedco2fixation pages 6-7): Ning Qin, Lingyun Li, Xiaozhen Wan, Xu Ji, Yu Chen, Chaokun Li, Ping Liu, Yijie Zhang, Weijie Yang, Junfeng Jiang, Jianye Xia, Shuobo Shi, Tianwei Tan, Jens Nielsen, Yun Chen, and Zihe Liu. Increased co2 fixation enables high carbon-yield production of 3-hydroxypropionic acid in yeast. Nature Communications, Feb 2024. URL: https://doi.org/10.1038/s41467-024-45557-9, doi:10.1038/s41467-024-45557-9. This article has 48 citations and is from a highest quality peer-reviewed journal.
(baek2016gsf2deletionincreases pages 2-3): Seung-Ho Baek, Eunice Y. Kwon, Seon-Young Kim, and Ji-Sook Hahn. Gsf2 deletion increases lactic acid production by alleviating glucose repression in saccharomyces cerevisiae. Scientific Reports, Oct 2016. URL: https://doi.org/10.1038/srep34812, doi:10.1038/srep34812. This article has 28 citations and is from a peer-reviewed journal.
(baek2016gsf2deletionincreases pages 1-2): Seung-Ho Baek, Eunice Y. Kwon, Seon-Young Kim, and Ji-Sook Hahn. Gsf2 deletion increases lactic acid production by alleviating glucose repression in saccharomyces cerevisiae. Scientific Reports, Oct 2016. URL: https://doi.org/10.1038/srep34812, doi:10.1038/srep34812. This article has 28 citations and is from a peer-reviewed journal.
(baek2016gsf2deletionincreases pages 6-7): Seung-Ho Baek, Eunice Y. Kwon, Seon-Young Kim, and Ji-Sook Hahn. Gsf2 deletion increases lactic acid production by alleviating glucose repression in saccharomyces cerevisiae. Scientific Reports, Oct 2016. URL: https://doi.org/10.1038/srep34812, doi:10.1038/srep34812. This article has 28 citations and is from a peer-reviewed journal.
(zhang2013thetranscriptionalcontrol pages 16-16): Lilin Zhang, Ningning Liu, Xiao Ma, and Linghuo Jiang. The transcriptional control machinery as well as the cell wall integrity and its regulation are involved in the detoxification of the organic solvent dimethyl sulfoxide in saccharomyces cerevisiae. FEMS yeast research, 13 2:200-18, Mar 2013. URL: https://doi.org/10.1111/1567-1364.12022, doi:10.1111/1567-1364.12022. This article has 55 citations and is from a peer-reviewed journal.
(baek2016gsf2deletionincreases pages 3-5): Seung-Ho Baek, Eunice Y. Kwon, Seon-Young Kim, and Ji-Sook Hahn. Gsf2 deletion increases lactic acid production by alleviating glucose repression in saccharomyces cerevisiae. Scientific Reports, Oct 2016. URL: https://doi.org/10.1038/srep34812, doi:10.1038/srep34812. This article has 28 citations and is from a peer-reviewed journal.
(kota2005specializedmembranelocalizedchaperones pages 5-6): Jhansi Kota and Per O. Ljungdahl. Specialized membrane-localized chaperones prevent aggregation of polytopic proteins in the er. The Journal of Cell Biology, 168:79-88, Jan 2005. URL: https://doi.org/10.1083/jcb.200408106, doi:10.1083/jcb.200408106. This article has 134 citations.
(kota2005specializedmembranelocalizedchaperones pages 7-8): Jhansi Kota and Per O. Ljungdahl. Specialized membrane-localized chaperones prevent aggregation of polytopic proteins in the er. The Journal of Cell Biology, 168:79-88, Jan 2005. URL: https://doi.org/10.1083/jcb.200408106, doi:10.1083/jcb.200408106. This article has 134 citations.

Citations

sherwood1999efficientexportof pages 2-3
sherwood1999efficientexportof pages 3-4
sherwood1999efficientexportof pages 4-5
kota2005specializedmembranelocalizedchaperones pages 6-7
gancedo1998yeastcarboncatabolite pages 11-12
gameiro2024genomewideconditionaldegron pages 5-6
zhang2013thetranscriptionalcontrol pages 16-16
sherwood1999efficientexportof pages 1-2
gonzalez2005phosphatetransportertraffic pages 10-11
gonzalez2005phosphatetransportertraffic pages 1-2
kota2005specializedmembranelocalizedchaperones pages 1-2
sherwood1999efficientexportof pages 5-6
kota2005specializedmembranelocalizedchaperones pages 5-6
kota2005specializedmembranelocalizedchaperones pages 7-8
ral membrane protein
w
https://doi.org/10.1073/pnas.96.13.7415
https://doi.org/10.1083/jcb.200408106
https://doi.org/10.1128/mmbr.62.2.334-361.1998
https://doi.org/10.1038/srep34812
https://doi.org/10.1111/1567-1364.12022
https://doi.org/10.1038/s41467-024-45557-9
https://doi.org/10.1083/jcb.202409007
https://doi.org/10.1105/tpc.105.036640
https://doi.org/10.1073/pnas.96.13.7415,
https://doi.org/10.1128/mmbr.62.2.334-361.1998,
https://doi.org/10.1105/tpc.105.036640,
https://doi.org/10.1083/jcb.200408106,
https://doi.org/10.1083/jcb.202409007,
https://doi.org/10.1038/s41467-024-45557-9,
https://doi.org/10.1038/srep34812,
https://doi.org/10.1111/1567-1364.12022,

📄 View Raw YAML

id: Q04697
gene_symbol: GSF2
product_type: PROTEIN
status: COMPLETE
taxon:
  id: NCBITaxon:559292
  label: Saccharomyces cerevisiae
description: >-
  GSF2, also known as ECM6, encodes an endoplasmic-reticulum membrane accessory
  factor required for efficient ER exit of selected polytopic hexose
  transporters. The best-supported clients are Hxt1 and Gal2: in gsf2 mutants,
  Hxt1 accumulates in the ER and Gal2 is mislocalized, whereas Hxt2 is much less
  affected. Mechanistic work places Gsf2 with cargo-specific membrane-localized
  chaperones such as Shr3, Pho86, and Chs7 that prevent aggregation or incorrect
  transmembrane-segment interactions in specific membrane-protein clients during
  ER biogenesis.
existing_annotations:
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: >-
      UniProt subcellular-location mapping to ER membrane is consistent with
      direct experimental evidence that Gsf2 is an integral ER membrane protein.
    action: ACCEPT
    reason: >-
      The ER membrane is the correct compartment for Gsf2's cargo-specific
      chaperone/accessory function in hexose-transporter biogenesis.
    supported_by:
    - reference_id: PMID:10377429
      supporting_text: >-
        We show that gsf2 mutants accumulate Hxt1p in the endoplasmic reticulum
        (ER) and that Gsf2p is a 46-kDa integral membrane protein localized to
        the ER.
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: IDA
  original_reference_id: PMID:10377429
  review:
    summary: >-
      Sherwood and Carlson experimentally localized Gsf2 as an integral ER
      membrane protein while showing that loss of GSF2 causes ER retention of
      Hxt1.
    action: ACCEPT
    reason: >-
      This is direct localization evidence for the core compartment where Gsf2
      acts.
    supported_by:
    - reference_id: PMID:10377429
      supporting_text: >-
        We show that gsf2 mutants accumulate Hxt1p in the endoplasmic reticulum
        (ER) and that Gsf2p is a 46-kDa integral membrane protein localized to
        the ER.
- term:
    id: GO:0005783
    label: endoplasmic reticulum
  evidence_type: HDA
  original_reference_id: PMID:26928762
  review:
    summary: >-
      The high-throughput ER localization is consistent with the better-supported
      ER membrane localization and the core ER function of Gsf2.
    action: ACCEPT
    reason: >-
      Although broader than ER membrane, this annotation remains correct and
      agrees with focused localization evidence.
    supported_by:
    - reference_id: PMID:10377429
      supporting_text: >-
        Gsf2p is a 46-kDa integral membrane protein localized to the ER.
- term:
    id: GO:0005737
    label: cytoplasm
  evidence_type: HDA
  original_reference_id: PMID:11914276
  review:
    summary: >-
      A broad cytoplasm annotation from a high-throughput localization study is
      not the best representation of Gsf2 biology. Focused studies and UniProt
      place Gsf2 in the ER membrane.
    action: MARK_AS_OVER_ANNOTATED
    reason: >-
      Gsf2 is an ER membrane protein with a cargo-specific function in ER export
      and folding of membrane transporters. The cytoplasm annotation is too broad
      and should not be treated as a core localization.
    supported_by:
    - reference_id: PMID:10377429
      supporting_text: >-
        Gsf2p is a 46-kDa integral membrane protein localized to the ER.
- term:
    id: GO:0005741
    label: mitochondrial outer membrane
  evidence_type: HDA
  original_reference_id: PMID:16407407
  review:
    summary: >-
      The mitochondrial outer membrane assignment is from a large-scale proteomic
      study and conflicts with focused experimental evidence for ER membrane
      localization and ER export function.
    action: REMOVE
    reason: >-
      No gene-specific evidence supports mitochondrial outer membrane localization
      for Gsf2. The experimentally supported localization is the ER membrane.
    supported_by:
    - reference_id: PMID:10377429
      supporting_text: >-
        These findings suggest that Gsf2p functions in the ER to promote the
        secretion of certain hexose transporters.
- term:
    id: GO:0006457
    label: protein folding
  evidence_type: IMP
  original_reference_id: PMID:15623581
  review:
    summary: >-
      Gsf2 acts as a cargo-specific membrane-localized chaperone that prevents
      aggregation of its cognate polytopic hexose-transporter substrates during
      ER membrane folding/biogenesis.
    action: ACCEPT
    reason: >-
      PMID:15623581 directly supports a protein folding/homeostasis role for Gsf2
      in the ER membrane, although the process should be interpreted as specific
      client maturation rather than general folding of all proteins.
    supported_by:
    - reference_id: PMID:15623581
      supporting_text: >-
        Also, we show that the integral ER proteins, Gsf2p, Pho86p, and Chs7p,
        function similarly to Shr3p. In cells individually lacking one of these
        components only their cognate substrates, hexose transporters, phosphate
        transporters, and chitin synthase-III, respectively, aggregate and
        consequently fail to exit the ER membrane.
- term:
    id: GO:0034394
    label: protein localization to cell surface
  evidence_type: IMP
  original_reference_id: PMID:10377429
  review:
    summary: >-
      Gsf2 is required for efficient ER export and plasma-membrane delivery of
      selected hexose transporters, especially Hxt1 and Gal2.
    action: ACCEPT
    reason: >-
      Loss of GSF2 causes Hxt1 retention in the ER and abnormal Gal2
      localization, supporting this biological-process annotation.
    supported_by:
    - reference_id: PMID:10377429
      supporting_text: >-
        gsf2 mutants accumulate Hxt1p in the endoplasmic reticulum (ER) ...
        gsf2 mutants also display a galactose growth defect and abnormal
        localization of the galactose transporter Gal2p.
- term:
    id: GO:0034394
    label: protein localization to cell surface
  evidence_type: IGI
  original_reference_id: PMID:10377429
  review:
    summary: >-
      The genetic interaction evidence with HXT1 is consistent with Gsf2's
      requirement for cell-surface delivery of selected hexose transporters.
    action: ACCEPT
    reason: >-
      HXT1 was isolated as a multicopy suppressor of a gsf2 mutation, and direct
      localization experiments showed Hxt1 ER accumulation in gsf2 mutants.
    supported_by:
    - reference_id: PMID:10377429
      supporting_text: >-
        We have isolated the HXT1 gene, which encodes a low-affinity,
        high-capacity glucose transporter, as a multicopy suppressor of a gsf2
        mutation.
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IMP
  original_reference_id: PMID:15623581
  review:
    summary: >-
      The evidence supports a specialized membrane-protein chaperone role rather
      than generic unfolded protein binding.
    action: MODIFY
    reason: >-
      Gsf2 prevents aggregation and inappropriate interactions of cognate
      polytopic hexose-transporter substrates in the ER membrane. GO:0044183
      protein folding chaperone captures the demonstrated client-specific
      chaperone function better than the broad GO:0051082 term.
    proposed_replacement_terms:
    - id: GO:0044183
      label: protein folding chaperone
    supported_by:
    - reference_id: PMID:15623581
      supporting_text: >-
        These findings indicate that polytopic membrane proteins depend on
        specialized membrane-localized chaperones to prevent inappropriate
        interactions between membrane-spanning segments as they insert and fold
        in the lipid bilayer of the ER membrane.
    - reference_id: file:yeast/GSF2/GSF2-deep-research-falcon.md
      supporting_text: >-
        **GSF2 (ECM6; YML048W)** encodes an **ER-localized integral membrane
        accessory/chaperone-like factor** that promotes proper folding/assembly
        and **efficient ER exit** of a **select subset of polytopic hexose
        transporters**, with strongest evidence for **Hxt1p** and effects on
        **Gal2p**
references:
- id: GO_REF:0000044
  title: >-
    Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location
    vocabulary mapping, accompanied by conservative changes to GO terms applied
    by UniProt
  findings: []
- id: PMID:10377429
  title: Efficient export of the glucose transporter Hxt1p from the endoplasmic reticulum requires Gsf2p
  findings:
  - statement: >-
      Gsf2 is an integral ER membrane protein required for ER export of Hxt1 and
      normal localization of Gal2.
    supporting_text: >-
      We show that gsf2 mutants accumulate Hxt1p in the endoplasmic reticulum
      (ER) and that Gsf2p is a 46-kDa integral membrane protein localized to the
      ER. gsf2 mutants also display a galactose growth defect and abnormal
      localization of the galactose transporter Gal2p.
- id: PMID:11914276
  title: Subcellular localization of the yeast proteome
  findings: []
- id: PMID:15623581
  title: Specialized membrane-localized chaperones prevent aggregation of polytopic proteins in the ER
  findings:
  - statement: >-
      Gsf2 acts with other substrate-specific ER membrane chaperones to prevent
      aggregation of cognate polytopic membrane protein substrates.
    supporting_text: >-
      In cells individually lacking one of these components only their cognate
      substrates, hexose transporters, phosphate transporters, and chitin
      synthase-III, respectively, aggregate and consequently fail to exit the ER
      membrane.
- id: PMID:16407407
  title: Proteomic analysis of the yeast mitochondrial outer membrane reveals accumulation of a subclass of preproteins
  findings: []
- id: PMID:26928762
  title: >-
    One library to make them all: streamlining the creation of yeast libraries
    via a SWAp-Tag strategy
  findings: []
- id: file:yeast/GSF2/GSF2-deep-research-falcon.md
  title: Falcon deep research report for GSF2
  findings:
  - statement: >-
      Falcon supports GSF2 as an ER-localized, cargo-specific accessory/chaperone
      factor for selected hexose transporters.
    supporting_text: >-
      GSF2 encodes an ER-localized integral membrane accessory/chaperone-like
      factor that promotes proper folding/assembly and efficient ER exit of a
      select subset of polytopic hexose transporters, with strongest evidence for
      Hxt1p and effects on Gal2p.
core_functions:
- description: >-
    Gsf2 is a cargo-specific ER membrane chaperone/accessory factor for selected
    polytopic hexose transporters. It prevents aggregation or incorrect
    transmembrane-segment interactions during ER membrane folding and enables
    efficient ER exit and cell-surface localization of clients such as Hxt1 and
    Gal2.
  molecular_function:
    id: GO:0044183
    label: protein folding chaperone
  directly_involved_in:
  - id: GO:0006457
    label: protein folding
  - id: GO:0034394
    label: protein localization to cell surface
  locations:
  - id: GO:0005789
    label: endoplasmic reticulum membrane
  supported_by:
  - reference_id: PMID:10377429
    supporting_text: >-
      These findings suggest that Gsf2p functions in the ER to promote the
      secretion of certain hexose transporters.
  - reference_id: PMID:15623581
    supporting_text: >-
      These findings indicate that polytopic membrane proteins depend on
      specialized membrane-localized chaperones to prevent inappropriate
      interactions between membrane-spanning segments as they insert and fold in
      the lipid bilayer of the ER membrane.
proposed_new_terms: []
suggested_questions:
- question: >-
    Which sequence or structural features of Hxt1 and Gal2 define dependence on
    Gsf2, and why is Hxt2 largely Gsf2-independent?
- question: >-
    Does Gsf2 directly bind its hexose-transporter clients during insertion, or
    does it act indirectly by recruiting ER export or quality-control machinery?
- question: >-
    How do the newer hydroxyurea and metabolic-engineering phenotypes connect to
    Gsf2's core ER membrane-protein biogenesis role?
suggested_experiments:
- description: >-
    Map Gsf2-client specificity using tagged Hxt1, Gal2, Hxt2, and transporter
    chimeras, measuring ER retention, aggregation, and plasma-membrane delivery
    in wild-type and gsf2 deletion cells.
  experiment_type: cell biology
- description: >-
    Perform crosslinking or proximity-labeling proteomics from functional tagged
    Gsf2 to identify direct transporter clients and ER export/quality-control
    partners.
  experiment_type: proteomics
- description: >-
    Test whether Gsf2-dependent transporter folding defects explain hydroxyurea
    recovery and organic-acid production phenotypes by separating transporter
    localization effects from downstream glucose-signaling changes.
  experiment_type: genetics

GSF2

Gene Description

Existing Annotations Review

Core Functions

References

Suggested Questions for Experts

Suggested Experiments

📚 Additional Documentation

Deep Research Falcon

Question

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

Target Gene/Protein Identity (from UniProt):

MANDATORY VERIFICATION STEPS:

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

Research Target:

Output

Gene Research for Functional Annotation

⚠️ CRITICAL: Gene/Protein Identification Context

Target Gene/Protein Identity (from UniProt):

MANDATORY VERIFICATION STEPS:

If Gene Symbol is Ambiguous or You Cannot Find Relevant Literature:

Research Target:

Research report: Functional annotation of Saccharomyces cerevisiae GSF2/ECM6 (UniProt Q04697; ORF YML048W)

0) Identity verification (critical disambiguation)

1) Key concepts and definitions (current understanding)

1.1 Cargo-specific ER accessory proteins / membrane-localized chaperones

1.2 Molecular role of Gsf2p (definition)

2) Molecular function, localization, substrates/clients, and pathway placement

2.1 Protein features and subcellular localization

2.2 Client (substrate) specificity: which transporters depend on Gsf2p?

2.3 Mechanism: ER export vs. membrane chaperone model

2.4 Connection to glucose signaling / carbon catabolite repression (CCR)

3) Recent developments (prioritizing 2023–2024)

3.1 2024 functional genomics: replication stress recovery / hydroxyurea resistance

3.2 2024 metabolic engineering: organic-acid production (3‑HP)

4) Current applications and real-world implementations

4.1 Strain engineering to alleviate glucose repression and improve organic-acid fermentation

4.2 Stress tolerance phenotypes used for functional screening

5) Expert opinions / authoritative synthesis (interpretive analysis)

5.1 Why a trafficking factor appears as a “glucose signaling” gene

5.2 Where in the cell Gsf2p acts and what it is not

6) Relevant statistics and data highlights (selected)

7) Visual evidence (primary paper figures)

8) Summary functional annotation (most defensible statement)

Evidence summary table

Citations

📄 View Raw YAML