Chitin synthase 1 (Chs1p) of Saccharomyces cerevisiae is a multi-pass plasma-membrane glycosyltransferase (GT2 family, class I chitin synthase) that polymerises beta-1,4-linked N-acetylglucosamine from UDP-GlcNAc (EC 2.4.1.16). It accounts for the bulk of chitin synthase activity measured in vitro (chitin synthase I, Mg2+-dependent, trypsin-activated zymogen) yet makes little chitin in vivo. Chs1p acts as a repair or auxiliary enzyme: after cell separation it replenishes chitin in the birth-scar region damaged by the periplasmic chitinase Cts1p at acidic pH, so chs1 null cells show bud lysis in unbuffered acidic medium. Chs1p resides both at the plasma membrane and in intracellular chitosomes (endosome-derived vesicles), with stable levels throughout the cell cycle. It cannot substitute for Chs2p in primary septum formation. CHS1 transcription is induced more than sixfold by mating pheromone through pheromone-responsive TGAAACA elements in its promoter, consistent with the increased chitin synthase zymogen and cell-wall chitin of pheromone-treated cells.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000920 septum digestion after cytokinesis | IMP PMID:2523889 Chitin synthase 1, an auxiliary enzyme for chitin synthesis ... | MARK AS OVER ANNOTATED | Summary: IMP from Cabib et al. 1989: chs1 disruptants lyse at the birth scar after cell separation because the chitinase that digests the septum damages the wall, and Chs1-dependent chitin synthesis normally repairs this damage. The phenotype places Chs1p at the septum-digestion step, but Chs1p does not perform septum digestion (the chitinase Cts1p does); it counteracts excessive digestion by repair synthesis. Reason: Chs1p is required to repair, not to execute, septum digestion. The annotation records a real phenotype linked to cell separation but over-states Chs1p's participation in the digestion process itself. Not removed because the curator read the full text and the mutant phenotype genuinely maps to this stage. Supporting Evidence: PMID:2523889 Because the presence of Chs1 in the cell abolishes lysis, it is concluded that damage to the cell wall is caused by excessive chitinase activity at acidic pH, which can normally be repaired through chitin synthesis by Chs1. PMID:2523889 The latter emerges as an auxiliary or emergency enzyme. |
| GO:0004100 chitin synthase activity | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PANTHER PTN001115588 (broad chitin synthase clade: fungal, insect, nematode, zebrafish). Chs1p has the conserved catalytic QRRRW motif and measured activity; inheritance is well supported. Supporting Evidence: PMID:9760183 Arginine residue mutations in Chs3p, and in Chs1p and Chs2p, resulted in a loss of both function in vivo and enzymatic activity. |
| GO:0004100 chitin synthase activity | IDA PMID:7952171 Subcellular localization, abundance and stability of chitin ... | ACCEPT | Summary: IDA from Leal-Morales et al. 1994: Chs1 activity measured in membrane fractions (chitosomes and plasma membrane) of wild-type cells. Supporting Evidence: PMID:7952171 Chs1 and Chs2 were both present in chitosomes and plasma membrane, but the relative distribution of each chitin synthetase in these two membranous populations varied. |
| GO:0004100 chitin synthase activity | IEA GO_REF:0000120 | ACCEPT | Summary: IEA from InterPro (IPR004835, IPR013616) / RHEA:16637 / EC 2.4.1.16. Correct for this class I chitin synthase. Supporting Evidence: file:yeast/CHS1/CHS1-uniprot.txt Polymerizes chitin, a structural polymer of the cell wall and |
| GO:0004100 chitin synthase activity | RCA GO_REF:0000123 | ACCEPT | Summary: RCA from YeastPathways chitin biosynthesis (PWY3O-15), placing Chs1p on the UDP-GlcNAc + chitin(n) -> chitin(n+1) + UDP reaction (EC 2.4.1.16). Correct. Supporting Evidence: PMID:2523889 Because the presence of Chs1 in the cell abolishes lysis, it is concluded that damage to the cell wall is caused by excessive chitinase activity at acidic pH, which can normally be repaired through chitin synthesis by Chs1. |
| GO:0005829 cytosol | RCA GO_REF:0000123 | REMOVE | Summary: RCA cytosol from the YeastPathways GO-CAM conversion default compartment. Chs1p is a multi-pass (7 TM) integral membrane protein of the plasma membrane and chitosomes; chitin polymerisation occurs at membranes with extrusion of the polymer, not in the cytosol. Reason: Pathway-default compartment contradicted by Chs1p's integral-membrane topology and experimentally determined membrane localization. Supporting Evidence: PMID:7952171 Chs1 and Chs2 were both present in chitosomes and plasma membrane, but the relative distribution of each chitin synthetase in these two membranous populations varied. file:yeast/CHS1/CHS1-uniprot.txt SUBCELLULAR LOCATION: Cell membrane {ECO:0000305|PubMed:2523889}; |
| GO:0005886 plasma membrane | IBA GO_REF:0000033 | ACCEPT | Summary: IBA from PANTHER PTN001115700 (fungal class I/II chitin synthases). Consistent with fractionation showing Chs1 in plasma membrane. Supporting Evidence: PMID:7952171 Chs1 and Chs2 were both present in chitosomes and plasma membrane, but the relative distribution of each chitin synthetase in these two membranous populations varied. |
| GO:0005886 plasma membrane | IDA PMID:8970154 Chs1p and Chs3p, two proteins involved in chitin synthesis, ... | ACCEPT | Summary: IDA from Ziman et al. 1996; Chs1p partitions between the plasma membrane and chitosomes. Supporting Evidence: PMID:8970154 Previous cell fractionation studies demonstrated that chitin synthase I activity (CSI) exists in a plasma membrane form and in intracellular membrane-bound particles called chitosomes. PMID:8970154 We found that Chs1p and Chs3p resided partly in chitosomes and that this distribution was not cell cycle regulated. |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: IEA from UniProt subcellular location (Cell membrane). Correct. Supporting Evidence: file:yeast/CHS1/CHS1-uniprot.txt SUBCELLULAR LOCATION: Cell membrane {ECO:0000305|PubMed:2523889}; |
| GO:0006031 chitin biosynthetic process | IBA GO_REF:0000033 | ACCEPT | Summary: IBA chitin biosynthetic process from the broad chitin synthase clade; Chs1p synthesizes chitin (repair synthesis in vivo). Supporting Evidence: PMID:2523889 Because the presence of Chs1 in the cell abolishes lysis, it is concluded that damage to the cell wall is caused by excessive chitinase activity at acidic pH, which can normally be repaired through chitin synthesis by Chs1. |
| GO:0006031 chitin biosynthetic process | RCA GO_REF:0000123 | ACCEPT | Summary: RCA from YeastPathways PWY3O-15 chitin biosynthesis. Correct; Chs1p catalyses the polymerization step. Supporting Evidence: PMID:2523889 Because the presence of Chs1 in the cell abolishes lysis, it is concluded that damage to the cell wall is caused by excessive chitinase activity at acidic pH, which can normally be repaired through chitin synthesis by Chs1. |
| GO:0016758 hexosyltransferase activity | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO (IPR004835 chitin synthase) maps to parent 'hexosyltransferase activity'. Correct but the specific child term chitin synthase activity is already established. Reason: Replace with chitin synthase activity. Proposed replacements: chitin synthase activity Supporting Evidence: PMID:7952171 Chs1 and Chs2 were both present in chitosomes and plasma membrane, but the relative distribution of each chitin synthetase in these two membranous populations varied. |
| GO:0030428 cell septum | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: IBA cell septum (is_active_in) from PANTHER PTN001115700, propagated mainly from Chs2-type enzymes that build the primary septum. Chs1p cannot substitute for Chs2p in septum formation, but it does act at the septum/birth-scar region in repair synthesis together with Chs2p. Reason: Defensible (repair synthesis at the septum region) but septum formation is Chs2's core role, not Chs1's; non-core. Supporting Evidence: PMID:2523889 Other experiments suggest that both Chs1 and Chs2 collaborate in the repair synthesis of chitin, whereas Chs1 cannot substitute for Chs2 in septum formation. |
| GO:0045009 chitosome | IDA PMID:8970154 Chs1p and Chs3p, two proteins involved in chitin synthesis, ... | ACCEPT | Summary: IDA from Ziman et al. 1996: Chs1p resides partly in chitosomes, an endocytic-derived compartment. Supporting Evidence: PMID:8970154 We found that Chs1p and Chs3p resided partly in chitosomes and that this distribution was not cell cycle regulated. |
| GO:0071944 cell periphery | HDA PMID:26928762 One library to make them all: streamlining the creation of y... | ACCEPT | Summary: HDA from the SWAT-tag library (Yofe et al. 2016) high-throughput localization; 'cell periphery' is consistent with plasma-membrane residence of Chs1p. Supporting Evidence: PMID:7952171 Chs1 and Chs2 were both present in chitosomes and plasma membrane, but the relative distribution of each chitin synthetase in these two membranous populations varied. |
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Download this section (compressed HTML)Q: What protease activates the Chs1p zymogen in vivo, and how is Chs1p activity restricted to the repair situation given its high in vitro activity?
Q: Is there a GO process term suitable for 'cell wall repair' after septum digestion that would better capture Chs1p's in vivo role than 'septum digestion after cytokinesis'?
Experiment: Live imaging of tagged Chs1p relative to Cts1p and the birth scar during cell separation in buffered vs acidic media, combined with chitin quantitation at birth scars in chs1 mutants.
Chitin synthase I; requires activation from zymogenic form in order to catalyze the transfer of N-acetylglucosamine (GlcNAc) to chitin; required for repairing the chitin septum during cytokinesis; transcription activated by mating factor
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