lac1 (UniProt O59735) encodes one of the two ceramide synthase subunits of fission yeast (Lag1 and Lac1; TLC-domain sphinganine N-acyltransferases), which acylate sphingoid bases with very-long-chain acyl-CoA to make ceramide. Lac1 and Lag1 co-immunoprecipitate and co-localise at the ER but make different ceramide and complex sphingolipid species. Lac1, but not Lag1, is needed for proper control of cell growth and size.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0005783 endoplasmic reticulum | EXP PMID:35008733 The Ceramide Synthase Subunit Lac1 Regulates Cell Growth and... | ACCEPT | Summary: Lac1 and Lag1 co-localise at the ER. Supporting Evidence: PMID:35008733 We showed that Lac1 and Lag1 co-immunoprecipitate and co-localize at the endoplasmic reticulum. |
| GO:0005783 endoplasmic reticulum | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT inference of ER localization; confirmed for S. pombe Lac1. Reason: ER is a root organelle term and the claim holds for this gene: Lac1-GFP co-localizes with the luminal ER marker mCherry-AHDL in S. pombe (PMID:35008733, the source of the separate EXP row, cited here as independent corroboration of the IBA), and UniProt records ER membrane localization by similarity with a multi-pass topology. Supporting Evidence: PMID:35008733 In rapidly growing cells, Lac1 and Lag1 co-localized completely with the ER marker (Figure 2B), confirming that ceramide synthase localizes at the ER in fission yeast. file:SCHPO/lac1/lac1-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane {ECO:0000250}; |
| GO:0005789 endoplasmic reticulum membrane | IEA GO_REF:0000044 | ACCEPT | Summary: ER membrane (UniProt subcellular location mapping). Reason: UniProt places Lac1 in the ER membrane by similarity (to the S. cerevisiae ceramide synthase subunits) as a multi-pass membrane protein, consistent with the predicted transmembrane helices; experimental co-localization with an ER marker in S. pombe (PMID:35008733) supports the ER part, and the multi-pass topology supports the membrane part. Supporting Evidence: file:SCHPO/lac1/lac1-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane {ECO:0000250}; file:SCHPO/lac1/lac1-uniprot.txt Multi-pass membrane protein {ECO:0000250}. PMID:35008733 In rapidly growing cells, Lac1 and Lag1 co-localized completely with the ER marker (Figure 2B), confirming that ceramide synthase localizes at the ER in fission yeast. |
| GO:0005789 endoplasmic reticulum membrane | NAS GO_REF:0000051 | ACCEPT | Summary: ER membrane (PomBase keyword mapping/author statement). Reason: Same claim as the IEA ER membrane row: UniProt places Lac1 in the ER membrane by similarity as a multi-pass membrane protein, and experimental co-localization with an ER marker in S. pombe (PMID:35008733) supports the ER part. Supporting Evidence: file:SCHPO/lac1/lac1-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane {ECO:0000250}; file:SCHPO/lac1/lac1-uniprot.txt Multi-pass membrane protein {ECO:0000250}. PMID:35008733 In rapidly growing cells, Lac1 and Lag1 co-localized completely with the ER marker (Figure 2B), confirming that ceramide synthase localizes at the ER in fission yeast. |
| GO:0016020 membrane | IEA GO_REF:0000002 | TOO GENERAL | Summary: Generic membrane; true but entailed by the endoplasmic reticulum membrane rows in this review. Reason: Correct but uninformative. Lac1 is a multi-pass membrane protein (seven predicted TRANSMEM segments; TLC domain, InterPro IPR006634) and S. pombe Lac1 co-localises with the ER marker (PMID:35008733). GO:0005789 endoplasmic reticulum membrane, asserted in this review, is part_of membrane. Supporting Evidence: PMID:35008733 In rapidly growing cells, Lac1 and Lag1 co-localized completely with the ER marker (Figure 2B), confirming that ceramide synthase localizes at the ER in fission yeast. file:SCHPO/lac1/lac1-uniprot.txt SUBCELLULAR LOCATION: Endoplasmic reticulum membrane {ECO:0000250}; file:SCHPO/lac1/lac1-uniprot.txt Multi-pass membrane protein {ECO:0000250}. |
| GO:0046513 ceramide biosynthetic process | EXP PMID:35008733 The Ceramide Synthase Subunit Lac1 Regulates Cell Growth and... | ACCEPT | Summary: Lac1 and Lag1 each make distinct ceramide species. Supporting Evidence: PMID:35008733 However, each protein generates different species of ceramides and complex sphingolipids. |
| GO:0046513 ceramide biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT inference of ceramide biosynthesis; supported by lipid analysis of lac1 deletion cells. Reason: Lipid labelling and ceramide-fraction analysis in S. pombe show lac1 deletion cells lack phytoceramide and the authors conclude Lac1 is the main ceramide synthase subunit (PMID:35008733); family membership (sphingosine N-acyltransferase family) matches the PAINT node. Supporting Evidence: PMID:35008733 In contrast, lac1∆ cells do not synthesize PH-Cer but generate both short- (lipid A) and long-chain DH-Cer (lipid B and C). PMID:35008733 Our genetic and lipid analysis strongly suggest that Lac1 is the fundamental subunit of the ceramide synthase in fission yeast. file:SCHPO/lac1/lac1-uniprot.txt SIMILARITY: Belongs to the sphingosine N-acyltransferase family. |
| GO:0046513 ceramide biosynthetic process | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro mapping (Lag1/Lac1-like family) to ceramide biosynthesis. Reason: The InterPro Lag1/Lac1-like family mapping is borne out for this gene: lac1 deletion cells lack phytoceramide and Lac1 is concluded to be the main ceramide synthase subunit in S. pombe (PMID:35008733). Supporting Evidence: PMID:35008733 In contrast, lac1∆ cells do not synthesize PH-Cer but generate both short- (lipid A) and long-chain DH-Cer (lipid B and C). PMID:35008733 Our genetic and lipid analysis strongly suggest that Lac1 is the fundamental subunit of the ceramide synthase in fission yeast. file:SCHPO/lac1/lac1-uniprot.txt SIMILARITY: Belongs to the sphingosine N-acyltransferase family. |
| GO:0050291 sphingosine N-acyltransferase activity | IBA GO_REF:0000033 | ACCEPT | Summary: Ceramide synthase (sphingoid base N-acyltransferase) activity (PAINT). Reason: Lac1 belongs to the sphingosine N-acyltransferase family and UniProt records the ceramide synthase reaction (EC 2.3.1.24). Direct enzyme assay of S. pombe Lac1 is not available; the in vivo evidence is that lac1 deletion cells fail to make phytoceramide from labelled sphingoid base, which the authors interpret as loss of the ceramide synthase step (PMID:35008733). Together with family membership this supports the activity. Supporting Evidence: file:SCHPO/lac1/lac1-uniprot.txt SIMILARITY: Belongs to the sphingosine N-acyltransferase family. file:SCHPO/lac1/lac1-uniprot.txt Reaction=sphing-4-enine + a fatty acyl-CoA = an N-acylsphing-4-enine PMID:35008733 Our genetic and lipid analysis strongly suggest that Lac1 is the fundamental subunit of the ceramide synthase in fission yeast. |
| GO:0050291 sphingosine N-acyltransferase activity | IEA GO_REF:0000120 | ACCEPT | Summary: Ceramide synthase (sphingoid base N-acyltransferase) activity (EC/Rhea mapping). Reason: Same claim as the IBA row: family membership (sphingosine N-acyltransferase family) and the UniProt-recorded EC 2.3.1.24 reaction, with in vivo lipid evidence that Lac1 is the main ceramide synthase subunit in S. pombe (PMID:35008733). Supporting Evidence: file:SCHPO/lac1/lac1-uniprot.txt SIMILARITY: Belongs to the sphingosine N-acyltransferase family. file:SCHPO/lac1/lac1-uniprot.txt Reaction=sphing-4-enine + a fatty acyl-CoA = an N-acylsphing-4-enine PMID:35008733 Our genetic and lipid analysis strongly suggest that Lac1 is the fundamental subunit of the ceramide synthase in fission yeast. |
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