JEM1

GO Term	Evidence	Action	Reason
GO:0051087 protein-folding chaperone binding	IBA GO_REF:0000033	ACCEPT	Summary: IBA is consistent with Jem1 as an ER J-domain co-chaperone for Kar2/BiP. Reason: J-domain co-chaperone function is the best-supported molecular role. Supporting Evidence: PMID:9148890 JEM1p likely assists the functions of BiP, Hsp70 in the ER, including karyogamy. file:yeast/JEM1/JEM1-deep-research-falcon.md Jem1p is an ER J-domain co-chaperone working within the Kar2/BiP chaperone system.
GO:0005783 endoplasmic reticulum	IBA GO_REF:0000033	ACCEPT	Summary: Phylogenetic inference agrees with direct ER membrane localization. Reason: The ER is the compartment for Jem1's folding, ERAD, and karyogamy functions. Supporting Evidence: PMID:9148890 protein was anchored in the endoplasmic reticulum (ER) membrane and its J-domain
GO:0034975 protein folding in endoplasmic reticulum	IBA GO_REF:0000033	ACCEPT	Summary: This matches Jem1/Scj1/Kar2 roles in ER folding and quality control. Reason: Jem1 supports ER folding and ERAD substrate handling. Supporting Evidence: PMID:11381090 Jem1p and Scj1p function as major partners for BiP in the ERAD process. PMID:9817751 Jem1p and Scj1p appear to have partially overlapping functions as cofactors for Kar2p.
GO:0051787 misfolded protein binding	IBA GO_REF:0000033	ACCEPT	Summary: Misfolded protein binding fits the ERAD substrate-solubility evidence. Reason: This term is more informative than generic unfolded protein binding for the ERAD role. Supporting Evidence: PMID:11381090 aberrant immature proteins aggregated and migrated in the densest fraction
GO:0005789 endoplasmic reticulum membrane	IEA GO_REF:0000044	ACCEPT	Summary: UniProt subcellular mapping is consistent with direct ER membrane evidence. Reason: Jem1 is a single-pass ER membrane protein with a lumen-facing J-domain. Supporting Evidence: PMID:9148890 protein was anchored in the endoplasmic reticulum (ER) membrane and its J-domain
GO:0031965 nuclear membrane	IEA GO_REF:0000044	KEEP AS NON CORE	Summary: Nuclear membrane localization is plausible but broad. Reason: Keep as valid context for karyogamy, but the ER membrane/nuclear outer membrane network terms are more precise. Supporting Evidence: PMID:15282802 localization data for 21 other proteins
GO:0005515 protein binding	IPI PMID:12493774 Nep98p is a component of the yeast spindle pole body and ess...	MARK AS OVER ANNOTATED	Summary: The MPS3/Nep98 interaction is relevant but GO:0005515 is uninformative. Reason: Protein binding hides the more specific J-domain co-chaperone and karyogamy biology. Supporting Evidence: PMID:12493774 screened for partner proteins for Jem1p by the yeast two-hybrid...identified Nep98p
GO:0036503 ERAD pathway	IMP PMID:11381090 Molecular chaperones in the yeast endoplasmic reticulum main...	ACCEPT	Summary: Direct ERAD assays support this process annotation. Reason: Jem1 helps keep soluble luminal ERAD substrates retrotranslocation competent. Supporting Evidence: PMID:11381090 one role for the lumenal Hsp70 chaperone system in the export of aberrant proteins
GO:0051082 unfolded protein binding	IMP PMID:9148890 The yeast JEM1p is a DnaJ-like protein of the endoplasmic re...	MODIFY	Summary: Unfolded protein binding is too broad for the evidence. Reason: Misfolded protein binding better captures Jem1's ERAD substrate-handling role. Proposed replacements: misfolded protein binding Supporting Evidence: PMID:11381090 BiP-Jem1p-Scj1p chaperone system is to retain ERAD substrates as lower molecular weight species.
GO:0051087 protein-folding chaperone binding	IGI PMID:9148890 The yeast JEM1p is a DnaJ-like protein of the endoplasmic re...	ACCEPT	Summary: Genetic evidence supports chaperone binding as the J-domain co-chaperone function. Reason: Jem1 works with Kar2/BiP during ER and nuclear fusion processes. Supporting Evidence: PMID:9148890 DnaJ-like proteins are functional partners for Hsp70 molecular chaperones.
GO:0005783 endoplasmic reticulum	HDA PMID:26928762 One library to make them all: streamlining the creation of y...	ACCEPT	Summary: High-throughput ER localization is consistent with direct evidence. Reason: ER localization is core to Jem1 function. Supporting Evidence: PMID:9148890 protein was anchored in the endoplasmic reticulum (ER) membrane
GO:0000742 karyogamy involved in conjugation with cellular fusion	IMP PMID:10069807 Genetic interactions between KAR7/SEC71, KAR8/JEM1, KAR5, an...	ACCEPT	Summary: Jem1/Kar8 has a defining role in nuclear fusion during mating. Reason: Karyogamy is a directly characterized JEM1 process, not a generic downstream phenotype. Supporting Evidence: PMID:10069807 Overexpression of KAR8/JEM1 (but not SEC63) strongly suppressed the mating...defect of kar2-1
GO:0005783 endoplasmic reticulum	IDA PMID:9148890 The yeast JEM1p is a DnaJ-like protein of the endoplasmic re...	ACCEPT	Summary: Direct experimental localization supports ER annotation. Reason: The ER is the core cellular compartment for Jem1. Supporting Evidence: PMID:9148890 protein was anchored in the endoplasmic reticulum (ER) membrane
GO:0034975 protein folding in endoplasmic reticulum	IGI PMID:9817751 A role for the DnaJ homologue Scj1p in protein folding in th...	ACCEPT	Summary: Genetic evidence supports overlapping Jem1/Scj1 ER folding functions. Reason: Jem1 and Scj1 are functionally overlapping ER DnaJ proteins. Supporting Evidence: PMID:9817751 Jem1p and Scj1p appear to have partially overlapping functions as cofactors for Kar2p.
GO:0042175 nuclear outer membrane-endoplasmic reticulum membrane network	IDA PMID:15282802 Localization of proteins that are coordinately expressed wit...	UNDECIDED	Summary: The ER/nuclear-envelope localization fits Jem1 biology, but the PMID:15282802 IDA claim cannot be independently verified from the accessible abstract. Reason: PMID:15282802 is a GFP localization survey whose accessible abstract does not name Jem1/KAR8, and the full text is unavailable here. PMID:9148890 supports ER membrane anchoring as biological context, but it does not directly verify this specific PMID:15282802 IDA localization record. Supporting Evidence: PMID:15282802 localization data for 21 other proteins PMID:9148890 protein was anchored in the endoplasmic reticulum (ER) membrane and its J-domain

Deep Research

Falcon

(JEM1-deep-research-falcon.md)

this with annotations you find in gene/protein databases, but these can be outdated or inaccurate. Falcon Edison Scientific Literature 25 citations 2026-05-04T10:19:28.583923

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 JEM1/KAR8 (YJL073W; UniProt P40358) in Saccharomyces cerevisiae (S288c)

0) Target verification (mandatory disambiguation)

The literature retrieved here unambiguously matches the UniProt-specified target: JEM1 (synonym KAR8; ORF YJL073W) encodes a DnaJ/Hsp40-family (“J-protein”) co-chaperone that is an ER membrane protein with a lumen-facing J-domain in Saccharomyces cerevisiae (S288c background), consistent with UniProt P40358’s description (nishikawa1997theyeastjem1p pages 1-2, nishikawa1997theyeastjem1p pages 2-3). No conflicting “JEM1” identity from other organisms is used in this report.

1) Key concepts and definitions (current mechanistic understanding)

1.1 J-proteins (Hsp40/DnaJ proteins) and the J-domain

J-proteins are co-chaperones that regulate Hsp70-family chaperones by engaging them through a conserved J-domain. In the ER lumen, the Hsp70 is Kar2/BiP, and ER J-proteins (including Jem1p) are thought to tune Kar2/BiP activity toward specific tasks (e.g., folding vs ERAD vs translocation) (nishikawa2001molecularchaperonesin pages 1-2, vembar2010jdomaincochaperone pages 1-2).

A canonical feature of J-domains is the His–Pro–Asp (HPD) motif, which is essential for functional interaction with Hsp70s. For Jem1p, mutation of the HPD motif (H613Q) abolishes Jem1p function in vivo (nishikawa1997theyeastjem1p pages 2-3, nishikawa1997theyeastjem1p pages 4-5).

1.2 ER protein quality control (ERQC) and ER-associated degradation (ERAD)

ERQC comprises folding and surveillance activities that prevent secretion of misfolded proteins; ERAD exports persistently misfolded ER proteins to the cytosol for proteasomal degradation. In yeast, an important mechanistic role for Kar2/BiP with the J-proteins Jem1p and Scj1p is to keep soluble misfolded luminal substrates soluble, preventing aggregation and maintaining them in a retrotranslocation-competent state (nishikawa2001molecularchaperonesin pages 1-2).

2) Gene/protein overview and cellular localization

2.1 Protein architecture and topology

Jem1p is reported as a 692-aa DnaJ-like protein with a single transmembrane segment and a C-terminal J-domain (nishikawa1997theyeastjem1p pages 1-2). Topology mapping shows Jem1p is anchored in the ER membrane with the J-domain facing the ER lumen; the luminal C-terminal region is glycosylated (nishikawa1997theyeastjem1p pages 4-5, nishikawa1997theyeastjem1p pages 2-3).

Two cropped figures from the primary paper visually support these conclusions:
- a domain schematic indicating the TM segment and the luminal J-domain (nishikawa1997theyeastjem1p media cb077d07)
- a microscopy panel showing the nuclear-fusion phenotype in mating (nishikawa1997theyeastjem1p media 2f50a63f)

2.2 Interaction partners and co-chaperone network

The best-supported partner is ER Hsp70 Kar2/BiP. Jem1p was proposed as a BiP (Kar2) and/or Lhs1 partner based on orientation and genetics (nishikawa1997theyeastjem1p pages 4-5), and later biochemically tested for BiP binding using a GST-Jem1p pulldown format (makio2008identificationandcharacterization pages 11-12). Jem1p also has partially overlapping functions with the soluble ER-lumen J-protein Scj1p: a jem1Δ scj1Δ double mutant is temperature sensitive, indicating redundancy or pathway buffering (nishikawa1997theyeastjem1p pages 2-3, nishikawa1997theyeastjem1p pages 4-5).

3) Primary biological functions and pathway placement

3.1 Primary function: ER-lumen J-protein co-chaperone for Kar2/BiP

The core molecular function supported by multiple studies is that Jem1p is an ER J-domain co-chaperone working within the Kar2/BiP chaperone system. Functional specificity among ER J-proteins is highlighted by data showing that a BiP surface mutation (R217A) disrupts interaction with Sec63 (translocation) while leaving Jem1p interaction and ERAD function largely intact—supporting the concept that different J-proteins specify distinct BiP functions (vembar2010jdomaincochaperone pages 1-2).

3.2 Karyogamy (nuclear fusion during mating)

Jem1p is required for karyogamy, specifically nuclear fusion during mating, consistent with the synonym KAR8 (nishikawa1997theyeastjem1p pages 1-2). Quantitatively, in a jem1Δ background 79% of zygotes contained two or more juxtaposed nuclei that failed to fuse, while cell fusion itself appeared normal (nishikawa1997theyeastjem1p pages 4-5). The HPD motif is required for this function: an HPD mutant (H613Q) cannot rescue the karyogamy defect (nishikawa1997theyeastjem1p pages 2-3). The karyogamy defect is visually illustrated in microscopy panels (nishikawa1997theyeastjem1p media 2f50a63f).

Mechanistically, later domain-dissection work indicates Jem1p has separable functional contributions to karyogamy versus ER quality control, with karyogamy linked to interactions mediated by the N-terminal region (and reported interaction with a nuclear-envelope-associated factor) while ERQC is more generally tied to the ER chaperone role (makio2008identificationandcharacterization pages 1-3).

3.3 ERAD and ERQC: substrate-class selectivity

A prominent mechanistic insight is substrate-class selectivity in ERAD:
- Soluble luminal ERAD substrates (e.g., CPY and related luminal clients) become stabilized and aggregate at elevated temperature when JEM1 and SCJ1 are deleted, similar to phenotypes in Kar2/BiP mutants (nishikawa2001molecularchaperonesin pages 1-2).
- In contrast, deletion of JEM1 + SCJ1 has little effect on ERAD of a membrane protein, implying Jem1p’s key contribution is maintaining solubility of luminal clients* rather than being a universal ERAD requirement across all substrate topologies (nishikawa2001molecularchaperonesin pages 1-2).

4) Phenotypes and quantitative/statistical evidence

Key low-throughput quantitative results supporting annotation include:
- Karyogamy defect: 79% of jem1Δ zygotes show unfused juxtaposed nuclei (nishikawa1997theyeastjem1p pages 4-5).
- Synthetic growth defect/redundancy: jem1Δ scj1Δ strains grow at 14–30 °C but fail at 37 °C, and the defect is rescued by a low-copy plasmid expressing tagged JEM1 (nishikawa1997theyeastjem1p pages 4-5).
- UPR/ER folding capacity readouts (contextual but quantitative): deletion of JEM1 is associated with constitutive UPR activation measured via KAR2 induction (~1.7-fold), and multi-J-protein mutant combinations further increase KAR2, supporting overlapping roles of luminal J-proteins in maintaining ER folding capacity (fama2007thesaccharomycescerevisiae pages 8-9). (These measurements are in a study centered on another ER J-protein but directly include Δjem1 quantitative effects.)

5) Current applications and real-world implementations

5.1 Yeast as an experimental platform to model ERAD and proteostasis

Jem1p is used as an experimentally tractable lever to interrogate ERAD mechanisms. A clear example is development of yeast expression systems for mammalian ENaC subunits, where Jem1/Scj1 were tested for roles in ERAD and ubiquitination of ENaC in yeast (buck2010theendoplasmicreticulum–associated pages 1-2, buck2010theendoplasmicreticulum–associated pages 2-3). This represents a real-world implementation of the Jem1/Scj1 axis as a model system for ER proteostasis relevant to human membrane proteins.

5.2 Using Jem1 mutants/epitope tagging to dissect co-chaperone mechanisms

The ENaC ERAD study explicitly employs epitope-tagged Jem1 constructs and HPD mutants (e.g., JEM1–3HA and JEM1H566Q–3HA in that paper’s construct set) together with UPR reporters and ERAD substrates, demonstrating how Jem1 is used operationally to map chaperone dependency and pathway wiring (buck2010theendoplasmicreticulum–associated pages 2-3).

6) Expert synthesis and authoritative interpretations

An authoritative review of yeast ER protein quality control/ERAD places Kar2/BiP together with Hsp40 co-chaperones Scj1 and Jem1 as supporting ERAD and the handling of misfolded proteins in the ER, emphasizing the integrated nature of the ER chaperone network in enabling retrotranslocation and degradation (makio2008identificationandcharacterization pages 12-12). The primary mechanistic studies support this review-level picture by providing substrate-class specificity (soluble luminal substrates) and genetic redundancy with Scj1 (nishikawa2001molecularchaperonesin pages 1-2, nishikawa1997theyeastjem1p pages 4-5).

7) Recent developments (2023–2024): evidence limitation in this run

Multiple targeted searches for 2023–2024 publications specifically about yeast JEM1/KAR8/YJL073W did not yield retrievable sources in the current tool run. Consequently, this report’s mechanistic conclusions rest on foundational primary work (1997–2010) and an authoritative review (2018). Any attempt to describe “latest research” beyond these sources would be speculative and is therefore not included.

8) Evidence-mapped summary table

Category	Key points (mechanism/definition)	Evidence/assays & quantitative data	Key sources (with year, DOI URL)
Verified identity	UniProt P40358 corresponds to Saccharomyces cerevisiae JEM1/KAR8/YJL073W, the ER-membrane DnaJ-like chaperone required for nuclear fusion; this matches the user-provided UniProt description and excludes ambiguity with other genes.	Primary paper identifies ORF YJL073W as JEM1, encoding a DnaJ-like ER membrane protein; nonessential singly, but functionally important in ER chaperoning and mating/karyogamy phenotypes (nishikawa1997theyeastjem1p pages 1-2, nishikawa1997theyeastjem1p pages 2-3).	Nishikawa & Endo 1997, J Biol Chem, https://doi.org/10.1074/jbc.272.20.12889 (nishikawa1997theyeastjem1p pages 1-2, nishikawa1997theyeastjem1p pages 2-3)
Protein type & domains	Jem1p is a DnaJ/Hsp40-family co-chaperone with a C-terminal J-domain, a conserved HPD motif required for activity, and a single transmembrane segment anchoring it in the ER membrane.	Reported as 692 aa with one putative TM segment and J-domain; H613Q substitution in the conserved HPD motif abolishes complementation of both growth and karyogamy defects, demonstrating that the J-domain is functionally essential (nishikawa1997theyeastjem1p pages 1-2, nishikawa1997theyeastjem1p pages 2-3).	Nishikawa & Endo 1997, https://doi.org/10.1074/jbc.272.20.12889 (nishikawa1997theyeastjem1p pages 1-2, nishikawa1997theyeastjem1p pages 2-3)
Subcellular localization & topology	Jem1p is an integral ER membrane protein with the J-domain exposed to the ER lumen; its lumenal C-terminal region is glycosylated. This orientation is consistent with a co-chaperone role for lumenal Hsp70s.	Epitope-tagging/immunolocalization and topology analysis showed ER-membrane anchoring with lumen-facing J-domain; glycosylation of the C-terminal/lumenal region was detected. Figure-level summary shows TM segment plus lumenal J-domain and mutant karyogamy phenotype (nishikawa1997theyeastjem1p pages 1-2, nishikawa1997theyeastjem1p pages 2-3, nishikawa1997theyeastjem1p pages 4-5, nishikawa1997theyeastjem1p media cb077d07).	Nishikawa & Endo 1997, https://doi.org/10.1074/jbc.272.20.12889 (nishikawa1997theyeastjem1p pages 1-2, nishikawa1997theyeastjem1p pages 2-3, nishikawa1997theyeastjem1p pages 4-5, nishikawa1997theyeastjem1p media cb077d07)
Primary molecular function	Jem1p is best understood as an ER J-domain co-chaperone that functionally partners with Kar2/BiP (and possibly Lhs1) to stimulate Hsp70-dependent ER processes; in ER quality control it helps maintain soluble lumenal substrates in a retrotranslocation-competent, non-aggregated state.	DnaJ proteins act through J-domains to regulate Hsp70 ATPase cycles; Jem1p was proposed as a partner for BiP/Kar2 and/or Lhs1. Later work showed BiP interaction with Jem1p and that BiP mutations can selectively disrupt one J-protein interaction (Sec63) while sparing Jem1, indicating mechanistic specificity among ER Hsp70–Hsp40 pairings (nishikawa1997theyeastjem1p pages 2-3, nishikawa1997theyeastjem1p pages 4-5, makio2008identificationandcharacterization pages 11-12, vembar2010jdomaincochaperone pages 1-2).	Nishikawa & Endo 1997, https://doi.org/10.1074/jbc.272.20.12889; Makio et al. 2008, https://doi.org/10.1111/j.1365-2443.2008.01223.x; Vembar et al. 2010, https://doi.org/10.1074/jbc.m110.102186 (nishikawa1997theyeastjem1p pages 2-3, nishikawa1997theyeastjem1p pages 4-5, makio2008identificationandcharacterization pages 11-12, vembar2010jdomaincochaperone pages 1-2)
Interaction partners	Best-supported partners are Kar2/BiP and the parallel ER J-protein Scj1; Lhs1 is a plausible/mentioned ER Hsp70 partner in the same chaperone network.	Genetic interaction: jem1Δ scj1Δ double mutants are temperature sensitive, indicating overlapping function. Biochemical support: GST-Jem1p-His pulldown conditions captured BiP/Kar2 binding. Reviews/primary context place Jem1p with Scj1, Sec63, Kar2, Lhs1 in the ER chaperone system (nishikawa1997theyeastjem1p pages 2-3, makio2008identificationandcharacterization pages 11-12, silberstein1998arolefor pages 1-2, nishikawa1997theyeastjem1p pages 4-5).	Makio et al. 2008, https://doi.org/10.1111/j.1365-2443.2008.01223.x; Nishikawa & Endo 1997, https://doi.org/10.1074/jbc.272.20.12889; Silberstein et al. 1998, https://doi.org/10.1083/jcb.143.4.921 (makio2008identificationandcharacterization pages 11-12, nishikawa1997theyeastjem1p pages 2-3, silberstein1998arolefor pages 1-2, nishikawa1997theyeastjem1p pages 4-5)
Karyogamy / nuclear fusion pathway	Jem1p has a specialized role in karyogamy, specifically nuclear membrane/nuclear fusion during mating. This is the source of the synonym KAR8. Its J-domain is required for this role.	In jem1Δ zygotes, 79% contained two or more juxtaposed nuclei that failed to fuse; crossing to wild type restored efficient diploid formation, indicating a bilateral mating defect. HPD mutant H613Q fails to rescue karyogamy. Figure panel summary shows juxtaposed unfused nuclei in the mutant (nishikawa1997theyeastjem1p pages 4-5, nishikawa1997theyeastjem1p pages 2-3, nishikawa1997theyeastjem1p media cb077d07).	Nishikawa & Endo 1997, https://doi.org/10.1074/jbc.272.20.12889 (nishikawa1997theyeastjem1p pages 4-5, nishikawa1997theyeastjem1p pages 2-3, nishikawa1997theyeastjem1p media cb077d07)
ER folding / protein quality control	Beyond karyogamy, Jem1p participates in ER protein folding/ER quality control (ERQC) with Scj1 and Kar2. Functional overlap with Scj1 explains why single mutants are mild but double mutants are stressed.	Primary and comparative work conclude Jem1p and Scj1 cooperate in ERQC; jem1Δ scj1Δ mutants display heat-sensitive growth and accumulation/aggregation of misfolded proteins in the ER lumen under restrictive conditions (makio2008identificationandcharacterization pages 1-3, nishikawa1997theyeastjem1p pages 4-5, nishikawa1997theyeastjem1p pages 2-3).	Makio et al. 2008, https://doi.org/10.1111/j.1365-2443.2008.01223.x; Nishikawa & Endo 1997, https://doi.org/10.1074/jbc.272.20.12889 (makio2008identificationandcharacterization pages 1-3, nishikawa1997theyeastjem1p pages 4-5, nishikawa1997theyeastjem1p pages 2-3)
ERAD role	Jem1p contributes to ER-associated degradation (ERAD) chiefly for soluble lumenal substrates, acting with Kar2/BiP and Scj1 to keep misfolded proteins soluble so they can be retrotranslocated and degraded.	In vivo/in vitro ERAD assays showed that when JEM1 and SCJ1 are deleted, soluble ERAD substrates such as CPY* and A1PiZ/pro-α-factor-based substrates become stabilized and aggregate at elevated temperature; authors conclude BiP/Jem1p/Scj1p maintain a retrotranslocation-competent state (nishikawa2001molecularchaperonesin pages 1-2).	Nishikawa et al. 2001, J Cell Biol, https://doi.org/10.1083/jcb.153.5.1061 (nishikawa2001molecularchaperonesin pages 1-2)
Substrate specificity	Jem1p’s ERAD contribution is substrate-class selective: important for soluble lumenal misfolded proteins, but much less important for at least some membrane ERAD substrates.	Deletion of JEM1 + SCJ1 had little effect on ERAD of a membrane protein, whereas soluble lumenal substrates were strongly impaired/stabilized. This supports a model in which Jem1p primarily buffers/solubilizes lumenal clients rather than serving as a general ERAD factor for all substrate topologies (nishikawa2001molecularchaperonesin pages 1-2).	Nishikawa et al. 2001, https://doi.org/10.1083/jcb.153.5.1061 (nishikawa2001molecularchaperonesin pages 1-2)
Genetic interactions & phenotypes	Key phenotypes: jem1Δ is viable but defective in karyogamy; jem1Δ scj1Δ is temperature sensitive at 37°C; HPD-mutant Jem1p is nonfunctional; ERQC/ERAD defects become prominent under heat/proteotoxic stress.	Growth assays showed the double disruptant grows at 14, 23, and 30°C but not 37°C; low-copy 3HA-JEM1 rescues. Microscopy quantified 79% unfused nuclei in jem1Δ zygotes. ERAD assays showed stabilization/aggregation of soluble substrates in the double mutant (nishikawa1997theyeastjem1p pages 4-5, nishikawa2001molecularchaperonesin pages 1-2).	Nishikawa & Endo 1997, https://doi.org/10.1074/jbc.272.20.12889; Nishikawa et al. 2001, https://doi.org/10.1083/jcb.153.5.1061 (nishikawa1997theyeastjem1p pages 4-5, nishikawa2001molecularchaperonesin pages 1-2)
UPR / stress context	Direct evidence that JEM1 itself is a canonical UPR regulator is limited in the retrieved Jem1-focused papers, but Jem1p clearly functions within the broader ER proteostasis stress network with Kar2 and Scj1. UPR-related conclusions are stronger for Scj1 and combined ER folding stress than for Jem1 alone.	Scj1 loss induces UPR and combined loss of Scj1/Jem1 exacerbates folding stress in the ER; reviews place Jem1 among ER proteostasis factors assisting Kar2 during ERQC/ERAD. Because direct Jem1-specific UPR regulation was not established in the core Jem1 primary papers retrieved, this annotation should be treated as contextual rather than primary (silberstein1998arolefor pages 1-2, makio2008identificationandcharacterization pages 1-3, nishikawa2001molecularchaperonesin pages 1-2).	Silberstein et al. 1998, https://doi.org/10.1083/jcb.143.4.921; Makio et al. 2008, https://doi.org/10.1111/j.1365-2443.2008.01223.x; Nishikawa et al. 2001, https://doi.org/10.1083/jcb.153.5.1061 (silberstein1998arolefor pages 1-2, makio2008identificationandcharacterization pages 1-3, nishikawa2001molecularchaperonesin pages 1-2)

Table: This table summarizes the experimentally supported functional annotation of Saccharomyces cerevisiae JEM1/KAR8/YJL073W (UniProt P40358), including topology, mechanism, pathways, interaction partners, and key phenotypes. It is useful as a compact evidence map linking core claims to primary sources and quantitative data.

9) Practical takeaways for functional annotation

Primary molecular role: Jem1p is an ER-membrane J-protein (Hsp40) whose luminal J-domain (HPD motif-dependent) supports Kar2/BiP-dependent proteostasis (nishikawa1997theyeastjem1p pages 4-5, nishikawa2001molecularchaperonesin pages 1-2).
Process-level functions: Jem1p is required for karyogamy/nuclear fusion during mating and participates in ERQC/ERAD (particularly for soluble luminal substrates) with partial redundancy to Scj1p (nishikawa1997theyeastjem1p pages 4-5, nishikawa2001molecularchaperonesin pages 1-2, nishikawa1997theyeastjem1p pages 2-3).
Localization: Jem1p is an ER membrane protein with lumen-facing J-domain, consistent with its roles in luminal folding and ERAD client management (nishikawa1997theyeastjem1p pages 4-5, nishikawa1997theyeastjem1p media cb077d07).

Key sources (publication date, URL)

Nishikawa S, Endo T. May 1997. J Biol Chem. “The Yeast JEM1p Is a DnaJ-like Protein of the Endoplasmic Reticulum Membrane Required for Nuclear Fusion.” https://doi.org/10.1074/jbc.272.20.12889 (nishikawa1997theyeastjem1p pages 4-5)
Nishikawa S, Fewell SW, Kato Y, Brodsky JL, Endo T. May 2001. J Cell Biol. “Molecular Chaperones in the Yeast Endoplasmic Reticulum Maintain the Solubility of Proteins for Retrotranslocation and Degradation.” https://doi.org/10.1083/jcb.153.5.1061 (nishikawa2001molecularchaperonesin pages 1-2)
Makio T, Nishikawa S, Nakayama T, Nagai H, Endo T. Oct 2008. Genes to Cells. “Identification and characterization of a Jem1p ortholog… dissection of Jem1p functions in karyogamy and protein quality control…” https://doi.org/10.1111/j.1365-2443.2008.01223.x (makio2008identificationandcharacterization pages 1-3, makio2008identificationandcharacterization pages 11-12)
Vembar SS, Jonikas MC, Hendershot LM, Weissman JS, Brodsky JL. Jul 2010. J Biol Chem. “J Domain Co-chaperone Specificity Defines the Role of BiP during Protein Translocation.” https://doi.org/10.1074/jbc.m110.102186 (vembar2010jdomaincochaperone pages 1-2)
Buck TM, Kolb AR, Boyd CR, Kleyman TR, Brodsky JL. Mar 2010. Mol Biol Cell. “The ERAD of the epithelial sodium channel requires a unique complement of molecular chaperones.” https://doi.org/10.1091/mbc.e09-11-0944 (buck2010theendoplasmicreticulum–associated pages 1-2)
Berner N, Reutter K-R, Wolf DH. Jun 2018. Annu Rev Biochem. “Protein Quality Control of the ER and ubiquitin-proteasome-triggered degradation…” https://doi.org/10.1146/annurev-biochem-062917-012749 (makio2008identificationandcharacterization pages 12-12)
Famá MC et al. Feb 2007. BBA - Mol Cell Res. “YFR041C/ERJ5 … required to preserve the folding capacity of the ER.” (includes Δjem1 quantitative UPR metrics) https://doi.org/10.1016/j.bbamcr.2006.10.011 (fama2007thesaccharomycescerevisiae pages 8-9)

References

(nishikawa1997theyeastjem1p pages 1-2): Shuh-ichi Nishikawa and Toshiya Endo. The yeast jem1p is a dnaj-like protein of the endoplasmic reticulum membrane required for nuclear fusion*. The Journal of Biological Chemistry, 272:12889-12892, May 1997. URL: https://doi.org/10.1074/jbc.272.20.12889, doi:10.1074/jbc.272.20.12889. This article has 137 citations.
(nishikawa1997theyeastjem1p pages 2-3): Shuh-ichi Nishikawa and Toshiya Endo. The yeast jem1p is a dnaj-like protein of the endoplasmic reticulum membrane required for nuclear fusion*. The Journal of Biological Chemistry, 272:12889-12892, May 1997. URL: https://doi.org/10.1074/jbc.272.20.12889, doi:10.1074/jbc.272.20.12889. This article has 137 citations.
(nishikawa2001molecularchaperonesin pages 1-2): Shuh-ichi Nishikawa, Sheara W. Fewell, Yoshihito Kato, Jeffrey L. Brodsky, and Toshiya Endo. Molecular chaperones in the yeast endoplasmic reticulum maintain the solubility of proteins for retrotranslocation and degradation. The Journal of Cell Biology, 153:1061-1070, May 2001. URL: https://doi.org/10.1083/jcb.153.5.1061, doi:10.1083/jcb.153.5.1061. This article has 442 citations.
(vembar2010jdomaincochaperone pages 1-2): Shruthi S. Vembar, Martin C. Jonikas, Linda M. Hendershot, Jonathan S. Weissman, and Jeffrey L. Brodsky. J domain co-chaperone specificity defines the role of bip during protein translocation. Journal of Biological Chemistry, 285:22484-22494, Jul 2010. URL: https://doi.org/10.1074/jbc.m110.102186, doi:10.1074/jbc.m110.102186. This article has 62 citations and is from a domain leading peer-reviewed journal.
(nishikawa1997theyeastjem1p pages 4-5): Shuh-ichi Nishikawa and Toshiya Endo. The yeast jem1p is a dnaj-like protein of the endoplasmic reticulum membrane required for nuclear fusion*. The Journal of Biological Chemistry, 272:12889-12892, May 1997. URL: https://doi.org/10.1074/jbc.272.20.12889, doi:10.1074/jbc.272.20.12889. This article has 137 citations.
(nishikawa1997theyeastjem1p media cb077d07): Shuh-ichi Nishikawa and Toshiya Endo. The yeast jem1p is a dnaj-like protein of the endoplasmic reticulum membrane required for nuclear fusion*. The Journal of Biological Chemistry, 272:12889-12892, May 1997. URL: https://doi.org/10.1074/jbc.272.20.12889, doi:10.1074/jbc.272.20.12889. This article has 137 citations.
(nishikawa1997theyeastjem1p media 2f50a63f): Shuh-ichi Nishikawa and Toshiya Endo. The yeast jem1p is a dnaj-like protein of the endoplasmic reticulum membrane required for nuclear fusion*. The Journal of Biological Chemistry, 272:12889-12892, May 1997. URL: https://doi.org/10.1074/jbc.272.20.12889, doi:10.1074/jbc.272.20.12889. This article has 137 citations.
(makio2008identificationandcharacterization pages 11-12): T. Makio, S. Nishikawa, T. Nakayama, Hiroyuki Nagai, and T. Endo. Identification and characterization of a jem1p ortholog of candida albicans: dissection of jem1p functions in karyogamy and protein quality control in saccharomyces cerevisiae. Genes to Cells, Oct 2008. URL: https://doi.org/10.1111/j.1365-2443.2008.01223.x, doi:10.1111/j.1365-2443.2008.01223.x. This article has 9 citations and is from a peer-reviewed journal.
(makio2008identificationandcharacterization pages 1-3): T. Makio, S. Nishikawa, T. Nakayama, Hiroyuki Nagai, and T. Endo. Identification and characterization of a jem1p ortholog of candida albicans: dissection of jem1p functions in karyogamy and protein quality control in saccharomyces cerevisiae. Genes to Cells, Oct 2008. URL: https://doi.org/10.1111/j.1365-2443.2008.01223.x, doi:10.1111/j.1365-2443.2008.01223.x. This article has 9 citations and is from a peer-reviewed journal.
(fama2007thesaccharomycescerevisiae pages 8-9): M. Carla Famá, David Raden, Nicolás Zacchi, Darío R. Lemos, Anne S. Robinson, and Susana Silberstein. The saccharomyces cerevisiae yfr041c/erj5 gene encoding a type i membrane protein with a j domain is required to preserve the folding capacity of the endoplasmic reticulum. Biochimica et Biophysica Acta (BBA) - Molecular Cell Research, 1773:232-242, Feb 2007. URL: https://doi.org/10.1016/j.bbamcr.2006.10.011, doi:10.1016/j.bbamcr.2006.10.011. This article has 41 citations and is from a peer-reviewed journal.
(buck2010theendoplasmicreticulum–associated pages 1-2): Teresa M. Buck, Alexander R. Kolb, Cary R. Boyd, Thomas R. Kleyman, and Jeffrey L. Brodsky. The endoplasmic reticulum–associated degradation of the epithelial sodium channel requires a unique complement of molecular chaperones. Molecular Biology of the Cell, 21:1047-1058, Mar 2010. URL: https://doi.org/10.1091/mbc.e09-11-0944, doi:10.1091/mbc.e09-11-0944. This article has 116 citations and is from a domain leading peer-reviewed journal.
(buck2010theendoplasmicreticulum–associated pages 2-3): Teresa M. Buck, Alexander R. Kolb, Cary R. Boyd, Thomas R. Kleyman, and Jeffrey L. Brodsky. The endoplasmic reticulum–associated degradation of the epithelial sodium channel requires a unique complement of molecular chaperones. Molecular Biology of the Cell, 21:1047-1058, Mar 2010. URL: https://doi.org/10.1091/mbc.e09-11-0944, doi:10.1091/mbc.e09-11-0944. This article has 116 citations and is from a domain leading peer-reviewed journal.
(makio2008identificationandcharacterization pages 12-12): T. Makio, S. Nishikawa, T. Nakayama, Hiroyuki Nagai, and T. Endo. Identification and characterization of a jem1p ortholog of candida albicans: dissection of jem1p functions in karyogamy and protein quality control in saccharomyces cerevisiae. Genes to Cells, Oct 2008. URL: https://doi.org/10.1111/j.1365-2443.2008.01223.x, doi:10.1111/j.1365-2443.2008.01223.x. This article has 9 citations and is from a peer-reviewed journal.
(silberstein1998arolefor pages 1-2): Susana Silberstein, Gabriel Schlenstedt, Pam A. Silver, and Reid Gilmore. A role for the dnaj homologue scj1p in protein folding in the yeast endoplasmic reticulum. The Journal of Cell Biology, 143:921-933, Nov 1998. URL: https://doi.org/10.1083/jcb.143.4.921, doi:10.1083/jcb.143.4.921. This article has 124 citations.

Citations

nishikawa2001molecularchaperonesin pages 1-2
makio2008identificationandcharacterization pages 11-12
vembar2010jdomaincochaperone pages 1-2
makio2008identificationandcharacterization pages 1-3
fama2007thesaccharomycescerevisiae pages 8-9
makio2008identificationandcharacterization pages 12-12
silberstein1998arolefor pages 1-2
https://doi.org/10.1074/jbc.272.20.12889
https://doi.org/10.1074/jbc.272.20.12889;
https://doi.org/10.1111/j.1365-2443.2008.01223.x;
https://doi.org/10.1074/jbc.m110.102186
https://doi.org/10.1083/jcb.143.4.921
https://doi.org/10.1083/jcb.153.5.1061
https://doi.org/10.1083/jcb.143.4.921;
https://doi.org/10.1111/j.1365-2443.2008.01223.x
https://doi.org/10.1091/mbc.e09-11-0944
https://doi.org/10.1146/annurev-biochem-062917-012749
https://doi.org/10.1016/j.bbamcr.2006.10.011
https://doi.org/10.1074/jbc.272.20.12889,
https://doi.org/10.1083/jcb.153.5.1061,
https://doi.org/10.1074/jbc.m110.102186,
https://doi.org/10.1111/j.1365-2443.2008.01223.x,
https://doi.org/10.1016/j.bbamcr.2006.10.011,
https://doi.org/10.1091/mbc.e09-11-0944,
https://doi.org/10.1083/jcb.143.4.921,

📄 View Raw YAML

id: P40358
gene_symbol: JEM1
product_type: PROTEIN
status: COMPLETE
aliases:
- KAR8
- YJL073W
taxon:
  id: NCBITaxon:559292
  label: Saccharomyces cerevisiae
description: >-
  JEM1/KAR8 encodes an ER membrane DnaJ/Hsp40-family co-chaperone with a
  lumen-facing J-domain. Jem1 works with the ER Hsp70 Kar2/BiP and overlaps
  partly with Scj1 to support ER protein folding and ERAD of soluble luminal
  misfolded substrates by keeping them soluble and retrotranslocation competent.
  Jem1 is also required for nuclear membrane fusion during mating karyogamy at
  the ER/nuclear envelope membrane system.
existing_annotations:
- term:
    id: GO:0051087
    label: protein-folding chaperone binding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: IBA is consistent with Jem1 as an ER J-domain co-chaperone for Kar2/BiP.
    action: ACCEPT
    reason: J-domain co-chaperone function is the best-supported molecular role.
    supported_by:
    - reference_id: PMID:9148890
      supporting_text: JEM1p likely assists the functions of BiP, Hsp70 in the ER, including karyogamy.
    - reference_id: file:yeast/JEM1/JEM1-deep-research-falcon.md
      supporting_text: Jem1p is an ER J-domain co-chaperone working within the Kar2/BiP chaperone system.
- term:
    id: GO:0005783
    label: endoplasmic reticulum
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: Phylogenetic inference agrees with direct ER membrane localization.
    action: ACCEPT
    reason: The ER is the compartment for Jem1's folding, ERAD, and karyogamy functions.
    supported_by:
    - reference_id: PMID:9148890
      supporting_text: protein was anchored in the endoplasmic reticulum (ER) membrane and its J-domain
- term:
    id: GO:0034975
    label: protein folding in endoplasmic reticulum
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: This matches Jem1/Scj1/Kar2 roles in ER folding and quality control.
    action: ACCEPT
    reason: Jem1 supports ER folding and ERAD substrate handling.
    supported_by:
    - reference_id: PMID:11381090
      supporting_text: Jem1p and Scj1p function as major partners for BiP in the ERAD process.
    - reference_id: PMID:9817751
      supporting_text: Jem1p and Scj1p appear to have partially overlapping functions as cofactors for Kar2p.
- term:
    id: GO:0051787
    label: misfolded protein binding
  evidence_type: IBA
  original_reference_id: GO_REF:0000033
  review:
    summary: Misfolded protein binding fits the ERAD substrate-solubility evidence.
    action: ACCEPT
    reason: This term is more informative than generic unfolded protein binding for the ERAD role.
    supported_by:
    - reference_id: PMID:11381090
      supporting_text: aberrant immature proteins aggregated and migrated in the densest fraction
- term:
    id: GO:0005789
    label: endoplasmic reticulum membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: UniProt subcellular mapping is consistent with direct ER membrane evidence.
    action: ACCEPT
    reason: Jem1 is a single-pass ER membrane protein with a lumen-facing J-domain.
    supported_by:
    - reference_id: PMID:9148890
      supporting_text: protein was anchored in the endoplasmic reticulum (ER) membrane and its J-domain
- term:
    id: GO:0031965
    label: nuclear membrane
  evidence_type: IEA
  original_reference_id: GO_REF:0000044
  review:
    summary: Nuclear membrane localization is plausible but broad.
    action: KEEP_AS_NON_CORE
    reason: Keep as valid context for karyogamy, but the ER membrane/nuclear outer membrane network terms are more precise.
    supported_by:
    - reference_id: PMID:15282802
      supporting_text: localization data for 21 other proteins
- term:
    id: GO:0005515
    label: protein binding
  evidence_type: IPI
  original_reference_id: PMID:12493774
  review:
    summary: The MPS3/Nep98 interaction is relevant but GO:0005515 is uninformative.
    action: MARK_AS_OVER_ANNOTATED
    reason: Protein binding hides the more specific J-domain co-chaperone and karyogamy biology.
    supported_by:
    - reference_id: PMID:12493774
      supporting_text: screened for partner proteins for Jem1p by the yeast two-hybrid...identified Nep98p
- term:
    id: GO:0036503
    label: ERAD pathway
  evidence_type: IMP
  original_reference_id: PMID:11381090
  review:
    summary: Direct ERAD assays support this process annotation.
    action: ACCEPT
    reason: Jem1 helps keep soluble luminal ERAD substrates retrotranslocation competent.
    supported_by:
    - reference_id: PMID:11381090
      supporting_text: one role for the lumenal Hsp70 chaperone system in the export of aberrant proteins
- term:
    id: GO:0051082
    label: unfolded protein binding
  evidence_type: IMP
  original_reference_id: PMID:9148890
  review:
    summary: Unfolded protein binding is too broad for the evidence.
    action: MODIFY
    reason: Misfolded protein binding better captures Jem1's ERAD substrate-handling role.
    proposed_replacement_terms:
    - id: GO:0051787
      label: misfolded protein binding
    supported_by:
    - reference_id: PMID:11381090
      supporting_text: BiP-Jem1p-Scj1p chaperone system is to retain ERAD substrates as lower molecular weight species.
- term:
    id: GO:0051087
    label: protein-folding chaperone binding
  evidence_type: IGI
  original_reference_id: PMID:9148890
  review:
    summary: Genetic evidence supports chaperone binding as the J-domain co-chaperone function.
    action: ACCEPT
    reason: Jem1 works with Kar2/BiP during ER and nuclear fusion processes.
    supported_by:
    - reference_id: PMID:9148890
      supporting_text: DnaJ-like proteins are functional partners for Hsp70 molecular chaperones.
- term:
    id: GO:0005783
    label: endoplasmic reticulum
  evidence_type: HDA
  original_reference_id: PMID:26928762
  review:
    summary: High-throughput ER localization is consistent with direct evidence.
    action: ACCEPT
    reason: ER localization is core to Jem1 function.
    supported_by:
    - reference_id: PMID:9148890
      supporting_text: protein was anchored in the endoplasmic reticulum (ER) membrane
- term:
    id: GO:0000742
    label: karyogamy involved in conjugation with cellular fusion
  evidence_type: IMP
  original_reference_id: PMID:10069807
  review:
    summary: Jem1/Kar8 has a defining role in nuclear fusion during mating.
    action: ACCEPT
    reason: Karyogamy is a directly characterized JEM1 process, not a generic downstream phenotype.
    supported_by:
    - reference_id: PMID:10069807
      supporting_text: Overexpression of KAR8/JEM1 (but not SEC63) strongly suppressed the mating...defect of kar2-1
- term:
    id: GO:0005783
    label: endoplasmic reticulum
  evidence_type: IDA
  original_reference_id: PMID:9148890
  review:
    summary: Direct experimental localization supports ER annotation.
    action: ACCEPT
    reason: The ER is the core cellular compartment for Jem1.
    supported_by:
    - reference_id: PMID:9148890
      supporting_text: protein was anchored in the endoplasmic reticulum (ER) membrane
- term:
    id: GO:0034975
    label: protein folding in endoplasmic reticulum
  evidence_type: IGI
  original_reference_id: PMID:9817751
  review:
    summary: Genetic evidence supports overlapping Jem1/Scj1 ER folding functions.
    action: ACCEPT
    reason: Jem1 and Scj1 are functionally overlapping ER DnaJ proteins.
    supported_by:
    - reference_id: PMID:9817751
      supporting_text: Jem1p and Scj1p appear to have partially overlapping functions as cofactors for Kar2p.
- term:
    id: GO:0042175
    label: nuclear outer membrane-endoplasmic reticulum membrane network
  evidence_type: IDA
  original_reference_id: PMID:15282802
  review:
    summary: The ER/nuclear-envelope localization fits Jem1 biology, but the PMID:15282802 IDA claim cannot be independently verified from the accessible abstract.
    action: UNDECIDED
    reason: PMID:15282802 is a GFP localization survey whose accessible abstract does not name Jem1/KAR8, and the full text is unavailable here. PMID:9148890 supports ER membrane anchoring as biological context, but it does not directly verify this specific PMID:15282802 IDA localization record.
    supported_by:
    - reference_id: PMID:15282802
      supporting_text: localization data for 21 other proteins
    - reference_id: PMID:9148890
      supporting_text: protein was anchored in the endoplasmic reticulum (ER) membrane and its J-domain
references:
- id: GO_REF:0000033
  title: Annotation inferences using phylogenetic trees
  findings: []
- id: GO_REF:0000044
  title: Gene Ontology annotation based on UniProtKB/Swiss-Prot Subcellular Location vocabulary mapping
  findings: []
- id: PMID:9148890
  title: The yeast JEM1p is a DnaJ-like protein of the endoplasmic reticulum membrane required for nuclear fusion.
  findings:
  - statement: Jem1 is an ER membrane DnaJ-like protein with a lumen-facing J-domain
    supporting_text: The JEM1 protein was anchored in the ER membrane and its J-domain faced the ER lumen.
- id: PMID:9817751
  title: A role for the DnaJ homologue Scj1p in protein folding in the yeast endoplasmic reticulum.
  findings:
  - statement: Jem1 and Scj1 have overlapping ER chaperone functions
    supporting_text: Cells lacking both Jem1p and Scj1p are temperature sensitive.
- id: PMID:11381090
  title: Molecular chaperones in the yeast endoplasmic reticulum maintain the solubility of proteins for retrotranslocation and degradation.
  findings:
  - statement: Jem1 and Scj1 maintain soluble ERAD substrates
    supporting_text: BiP cooperates with Jem1p and Scj1p to facilitate export of ERAD substrates by preventing aggregation in the ER lumen.
- id: PMID:10069807
  title: Genetic interactions between KAR7/SEC71, KAR8/JEM1, KAR5, and KAR2 during nuclear fusion in Saccharomyces cerevisiae.
  findings:
  - statement: JEM1/KAR8 genetically interacts with KAR2 during nuclear fusion
    supporting_text: Overexpression of KAR8/JEM1 strongly suppressed the mating defect of kar2-1.
- id: PMID:12493774
  title: Nep98p is a component of the yeast spindle pole body and essential for nuclear division and fusion.
  findings: []
- id: PMID:15282802
  title: Localization of proteins that are coordinately expressed with Cln2 during the cell cycle.
  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/JEM1/JEM1-deep-research-falcon.md
  title: Falcon deep research report for JEM1
  findings:
  - statement: Jem1 is an ER J-domain co-chaperone for Kar2/BiP
    supporting_text: The report identifies ER J-domain co-chaperone activity within the Kar2/BiP system as Jem1's best-supported molecular role.
core_functions:
- description: >-
    ER membrane J-domain co-chaperone activity in the Kar2/BiP system. Jem1 helps
    maintain soluble luminal misfolded proteins for ERAD and overlaps with Scj1
    in ER protein folding.
  molecular_function:
    id: GO:0051087
    label: protein-folding chaperone binding
  directly_involved_in:
  - id: GO:0034975
    label: protein folding in endoplasmic reticulum
  - id: GO:0036503
    label: ERAD pathway
  locations:
  - id: GO:0005789
    label: endoplasmic reticulum membrane
  supported_by:
  - reference_id: PMID:11381090
    supporting_text: Jem1p and Scj1p function as major partners for BiP in the ERAD process.
  - reference_id: file:yeast/JEM1/JEM1-deep-research-falcon.md
    supporting_text: Jem1 is an ER J-domain co-chaperone in the Kar2/BiP system.
- description: J-domain-dependent support of nuclear membrane fusion during mating karyogamy.
  molecular_function:
    id: GO:0051087
    label: protein-folding chaperone binding
  directly_involved_in:
  - id: GO:0000742
    label: karyogamy involved in conjugation with cellular fusion
  locations:
  - id: GO:0005789
    label: endoplasmic reticulum membrane
  supported_by:
  - reference_id: PMID:10069807
    supporting_text: Overexpression of KAR8/JEM1 (but not SEC63) strongly suppressed the mating...defect of kar2-1
proposed_new_terms: []
suggested_questions:
- question: Should JEM1/SCJ1-like ER J-proteins use GO:0051787 rather than GO:0051082 when the evidence is ERAD substrate solubility?
suggested_experiments: []

Gene Description

Existing Annotations Review

Core Functions

ER membrane J-domain co-chaperone activity in the Kar2/BiP system. Jem1 helps maintain soluble luminal misfolded proteins for ERAD and overlaps with Scj1 in ER protein folding.

J-domain-dependent support of nuclear membrane fusion during mating karyogamy.