KEI1 (YDR367W) encodes an essential multi-pass medial-Golgi membrane protein that is the non-catalytic regulatory subunit of inositol phosphorylceramide (IPC) synthase. It forms a complex with the catalytic subunit Aur1 and is required both for IPC synthase activity (Aur1 alone has hardly detectable activity) and for retaining Aur1 in the Golgi, where phosphoinositol is transferred from phosphatidylinositol to ceramide to make IPC, the first complex sphingolipid. Kei1 is cleaved by Kex2 into N- and C-terminal chains after Arg-135, recycles between medial and late Golgi via COPI, and the temperature-sensitive kei1-1 allele confers aureobasidin A hypersensitivity and a thermolabile IPC synthase.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000139 Golgi membrane | IBA GO_REF:0000033 | ACCEPT | Summary: IBA is_active_in Golgi membrane from PTN001998811 (yeast KEI1 donor). Correct. Reason: Site of IPC synthesis. Supporting Evidence: PMID:19726565 We find that Kei1 is localized in the medial-Golgi and that Kei1 is cleaved by Kex2 |
| GO:0000139 Golgi membrane | IDA PMID:19726565 Kei1: a novel subunit of inositolphosphorylceramide synthase... | ACCEPT | Summary: Sato et al. 2009 IDA: Kei1 is a medial-Golgi membrane protein that recycles between medial and late Golgi (Kex2-cleaved). Reason: Core location. Supporting Evidence: PMID:19726565 We find that Kei1 is localized in the medial-Golgi and that Kei1 is cleaved by Kex2 |
| GO:0000139 Golgi membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt SubCell 'Golgi apparatus membrane' mapping. Correct. Reason: Correct. Supporting Evidence: file:yeast/KEI1/KEI1-uniprot.txt SUBCELLULAR LOCATION: Golgi apparatus membrane |
| GO:0005515 protein binding | IPI PMID:19726565 Kei1: a novel subunit of inositolphosphorylceramide synthase... | MODIFY | Summary: Sato et al. 2009 IPI with Aur1 (P36107), the catalytic IPC synthase subunit. The interaction is real and functionally important, but 'protein binding' does not express it; Kei1 binding is what makes Aur1 active and Golgi-retained. Reason: Replace uninformative protein binding with the regulator activity that the Aur1 interaction underlies. Proposed replacements: inositol phosphoceramide synthase regulator activity Supporting Evidence: PMID:19726565 Aur1 and Kei1 proteins form a complex in vivo PMID:19726565 Aur1 without Kei1 has hardly detectable IPC synthase activity |
| GO:0005515 protein binding | IPI PMID:37968396 The social and structural architecture of the yeast protein ... | REMOVE | Summary: Michaelis et al. 2023 high-throughput AP-MS interaction of Kei1 with Aur1. Correct interaction, uninformative term; the complex membership is captured by GO:0070916. Reason: Uninformative protein binding term; removal does not mean the interaction is false. Supporting Evidence: PMID:19726565 Aur1 and Kei1 proteins form a complex in vivo |
| GO:0005737 cytoplasm | HDA PMID:14562095 Global analysis of protein localization in budding yeast. | KEEP AS NON CORE | Summary: Huh et al. 2003 HDA 'cytoplasm'. Kei1 is a Golgi membrane protein, and the Golgi lies within the cytoplasm, so the term is true but uninformative. Reason: True but uninformative; Golgi membrane is the precise location. Supporting Evidence: PMID:19726565 We find that Kei1 is localized in the medial-Golgi and that Kei1 is cleaved by Kex2 |
| GO:0005794 Golgi apparatus | HDA PMID:14690591 Assigning function to yeast proteins by integration of techn... | ACCEPT | Summary: Hazbun et al. 2003 HDA (integrated localisation of essential uncharacterised ORFs): Golgi apparatus. Consistent with later work. Reason: Correct. Supporting Evidence: PMID:19726565 We find that Kei1 is localized in the medial-Golgi and that Kei1 is cleaved by Kex2 |
| GO:0006673 inositol phosphoceramide metabolic process | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN001998811. Kei1 is required for IPC synthesis; GO has no IPC biosynthetic process term, so this metabolic process term is the best available. Reason: Correct. Supporting Evidence: PMID:19726565 we conclude that Kei1 is essential for both the activity and the Golgi localization of IPC synthase |
| GO:0006673 inositol phosphoceramide metabolic process | IDA PMID:19726565 Kei1: a novel subunit of inositolphosphorylceramide synthase... | ACCEPT | Summary: Sato et al. 2009 IDA: IPC synthase activity in kei1-1 membranes is thermolabile. Reason: Correct. Supporting Evidence: PMID:19726565 The kei1-1 mutant is hypersensitive to aureobasidin A, a specific inhibitor of IPC synthesis, and the IPC synthase activity in the mutant membranes is thermolabile |
| GO:0006673 inositol phosphoceramide metabolic process | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro IPR013862 (Kei1 family) mapping. Correct. Reason: Correct. Supporting Evidence: file:yeast/KEI1/KEI1-uniprot.txt FUNCTION: Regulatory component of the inositol phosphorylceramide (ICP) |
| GO:0006673 inositol phosphoceramide metabolic process | IMP PMID:19726565 Kei1: a novel subunit of inositolphosphorylceramide synthase... | ACCEPT | Summary: Sato et al. 2009 IMP: kei1-1 mutants are aureobasidin A hypersensitive and have thermolabile IPC synthase. Reason: Correct. Supporting Evidence: PMID:19726565 The kei1-1 mutant is hypersensitive to aureobasidin A, a specific inhibitor of IPC synthesis, and the IPC synthase activity in the mutant membranes is thermolabile |
| GO:0030148 sphingolipid biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: IBA sphingolipid biosynthetic process (PTN001998811). IPC formation is the first complex-sphingolipid step; correct parent process. Reason: Correct. Supporting Evidence: PMID:19726565 we conclude that Kei1 is essential for both the activity and the Golgi localization of IPC synthase |
| GO:0030148 sphingolipid biosynthetic process | IPI PMID:19726565 Kei1: a novel subunit of inositolphosphorylceramide synthase... | ACCEPT | Summary: Sato et al. 2009 (IPI evidence code) for sphingolipid biosynthesis, based on the Aur1-Kei1 complex. Correct process. Reason: Correct. Supporting Evidence: PMID:19726565 Aur1 and Kei1 proteins form a complex in vivo PMID:19726565 we conclude that Kei1 is essential for both the activity and the Golgi localization of IPC synthase |
| GO:0070916 inositol phosphoceramide synthase complex | IBA GO_REF:0000033 | ACCEPT | Summary: IBA part_of IPC synthase complex (PTN001998811). Correct. Reason: Core complex. Supporting Evidence: PMID:19726565 we show that an essential protein encoded by KEI1 is a novel subunit of IPC synthase of Saccharomyces cerevisiae |
| GO:0070916 inositol phosphoceramide synthase complex | IPI PMID:19726565 Kei1: a novel subunit of inositolphosphorylceramide synthase... | ACCEPT | Summary: Sato et al. 2009 IPI: Kei1 forms a complex with Aur1 in vivo. Reason: Core complex. Supporting Evidence: PMID:19726565 Aur1 and Kei1 proteins form a complex in vivo |
| GO:0070916 inositol phosphoceramide synthase complex | IPI PMID:19726565 Kei1: a novel subunit of inositolphosphorylceramide synthase... | ACCEPT | Summary: Sato et al. 2009 IPI with AUR1 (SGD:S000001487). Correct. Reason: Core complex. Supporting Evidence: PMID:19726565 Aur1 and Kei1 proteins form a complex in vivo |
| GO:0070917 inositol phosphoceramide synthase regulator activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PTN001998811. Correct. Reason: Core MF. Supporting Evidence: PMID:19726565 Aur1 without Kei1 has hardly detectable IPC synthase activity |
| GO:0070917 inositol phosphoceramide synthase regulator activity | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro IPR013862 (Kei1 family) mapping. Correct. Reason: Core MF. Supporting Evidence: file:yeast/KEI1/KEI1-uniprot.txt FUNCTION: Regulatory component of the inositol phosphorylceramide (ICP) |
| GO:0070917 inositol phosphoceramide synthase regulator activity | IMP PMID:19726565 Kei1: a novel subunit of inositolphosphorylceramide synthase... | ACCEPT | Summary: Sato et al. 2009 IMP: Aur1 without Kei1 has hardly detectable IPC synthase activity. Reason: Core MF; Kei1 is an essential activating subunit. Supporting Evidence: PMID:19726565 Aur1 without Kei1 has hardly detectable IPC synthase activity PMID:19726565 we conclude that Kei1 is essential for both the activity and the Golgi localization of IPC synthase |
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Download this section (compressed HTML)Q: Does Kei1 contribute residues to the Aur1 active site (making it a co-catalytic rather than purely regulatory subunit), as structural studies of the Aur1-Kei1 complex might resolve?
Experiment: Purify Aur1 with wild-type Kei1, kei1-1 and Golgi-retention-defective Kei1 variants and compare IPC synthase kinetics in detergent micelles independent of localisation.
Hypothesis: Kei1 is required for Aur1 folding or active-site conformation rather than only localisation
Type: biochemistry
Component of inositol phosphorylceramide (IPC) synthase; forms a complex with Aur1p and regulates its activity; required for IPC synthase complex localization to the Golgi; post-translationally processed by Kex2p; KEI1 is an essential gene
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