Bgs4 (also called Cwg1, Orb11 and Pbr1) is one of the four Schizosaccharomyces pombe 1,3-beta-glucan synthases (Bgs1-4), large plasma membrane proteins of glycosyltransferase family 48 (FKS family) with 16 predicted transmembrane helices. Bgs4 is essential and accounts for most of the membrane 1,3-beta-glucan synthase activity of the cell. It is required for the major branched beta-1,3-glucan of the cell wall, which gives the cell its shape and mechanical integrity. Bgs4 localizes to the plasma membrane of the growing cell tips in interphase and moves, through the late Golgi, to the division site after contractile ring assembly and septum initiation. There it builds the secondary septum and reinforces the edge of the primary septum. Loss of Bgs4 thins the wall at the poles and abolishes the secondary septum; cells lyse at growing poles and mainly at the septum around cell separation. Bgs4-derived glucan is also needed to keep the actomyosin ring correctly positioned and coupled to septum growth. Bgs4 is also found at mating projections, the zygote fusion site, forming spore walls and the germinating spore. Like other FKS synthases it is activated by the Rho1 GTPase, the regulatory subunit of the glucan synthase. Bgs4 is the target of the antifungal glucan synthase inhibitors papulacandin B, enfumafungin and the echinocandins; point mutations in bgs4 (pbr1 alleles) confer resistance.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000148 1,3-beta-D-glucan synthase complex | IEA GO_REF:0000002 | ACCEPT | Summary: InterPro2GO mapping from the glycosyltransferase 48 domain (IPR003440) to the 1,3-beta-D-glucan synthase complex. Reason: Bgs4 is a full-length GT48 (FKS) catalytic subunit. Cortes et al. 2005 found Bgs4 to be the only Bgs subunit shown to be part of the membrane GS enzyme and argued that it forms part of a GS catalytic multiprotein complex, so the complex term is sound. Supporting Evidence: file:SCHPO/bgs4/bgs4-uniprot.txt InterPro; IPR003440; Glyco_trans_48_dom. PMID:15615781 Bgs4p is the only subunit found to be a part of the GS enzyme and essential for maintaining cell integrity during cytokinesis and polarized growth PMID:15615781 Bgs4p forms part of a GS catalytic multiprotein complex |
| GO:0000148 1,3-beta-D-glucan synthase complex | NAS GO_REF:0000051 | ACCEPT | Summary: S. pombe keyword mapping placing Bgs4 in the 1,3-beta-D-glucan synthase complex. Reason: Same claim as the IEA row and consistent with it. Bgs4 is the catalytic subunit of the Rho1-activated GS complex; Rho1 is the regulatory subunit. Supporting Evidence: file:SCHPO/bgs4/bgs4-uniprot.txt SUBUNIT: Component of the 1,3-beta-glucan synthase (GS) complex, PMID:15615781 Bgs4p is the only subunit found to be a part of the GS enzyme and essential for maintaining cell integrity during cytokinesis and polarized growth PMID:35049972 the essential GTPase Rho1 is the Ξ²-GS regulatory subunit responsible for the activation of GS catalytic subunits Bgs1 to Bgs4 |
| GO:0000935 division septum | IDA PMID:15615781 The novel fission yeast (1,3)beta-D-glucan synthase catalyti... | ACCEPT | Summary: GFP-Bgs4 at the medial ring and the growing septum (Cortes et al. 2005). Reason: Bgs4 relocalizes from the cell ends to the assembling septum after contractile ring formation and arrives after septum initiation. It makes the septum branched beta-1,3-glucan and is required for the secondary septum. Light microscopy cannot separate the plasma membrane lining the septum from the septum itself; the division septum term is PomBase practice for septum synthases and correctly names where Bgs4 acts. Supporting Evidence: PMID:15615781 Bgs4p localizes to the growing ends, the medial ring and septum, and at each stage of wall synthesis or remodeling that occurs during sexual differentiation file:SCHPO/bgs4/bgs4-uniprot.txt Following nuclear division and formation of the contractile ring, relocalizes from the cell ends to the assembling division septum. PMID:24165938 Bgs4-derived Ξ²(1,3)glucan is essential for secondary septum formation and correct primary septum completion. |
| GO:0000936 primary cell septum | IDA PMID:24165938 Extracellular cell wall Ξ²(1,3)glucan is required to couple s... | KEEP AS NON CORE | Summary: Bgs4 at the primary septum (Munoz et al. 2013). Reason: Full text cached. Bgs4-derived branched glucan is needed for correct primary septum completion and for the integrity of the primary septum base where it anchors to the wall, and the PomBase GO-CAM places Bgs4 activity in the primary septum. Its main septal role is the secondary septum (Bgs1 makes the primary septum linear glucan), so this is kept as a correct but non-core location. Supporting Evidence: PMID:24165938 Bgs4 is responsible for the SS formation and necessary for the integrity of the PS base needed for its anchorage into the cell wall. PMID:24165938 Bgs4-derived Ξ²(1,3)glucan is essential for secondary septum formation and correct primary septum completion. |
| GO:0003843 1,3-beta-D-glucan synthase activity | IBA GO_REF:0000033 | MODIFY | Summary: PAINT IBA placing 1,3-beta-glucan synthase activity at the fungal FKS node (sources include S. cerevisiae Fks1/Gsc2, C. albicans Gsc1 and S. pombe Bgs1, Bgs3, Bgs4). Reason: The activity is correct and ancestral; Bgs4 is a full-length GT48 member and its own experimental annotation is among the sources, as expected. But the gene carries the more specific child GO:0140752 branched 1,3-beta-D-glucan synthase activity (TAS, PMID:34959732), which is_a this term, so the row is refined to it. The branched-product assignment rests on the composition of the walls of bgs4 mutants and on Bgs4 carrying most membrane GS activity, not on a reconstituted enzyme; whether Bgs4 itself makes the beta-1,6 branch points, or relies on a partner remodeler as Bgs3 relies on Ghs2, is open (Ghs2 does not co-immunoprecipitate with Bgs4). Propagation Review Root cause: NO FAILURE CORE Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN001272353 SUPPORTS TRANSFER Fungal FKS node; beta-1,3-glucan synthase activity is ancestral and Bgs4 is inside the clade. MODIFY only refines to the branched child that PomBase uses for Bgs4. Proposed replacements: branched 1,3-beta-D-glucan synthase activity Supporting Evidence: file:SCHPO/bgs4/bgs4-uniprot.txt Pfam; PF02364; Glucan_synthase; 1. PMID:34959732 It synthesizes the branched Ξ²(1,3)-D-glucan and is responsible for most GS activity |
| GO:0003843 1,3-beta-D-glucan synthase activity | IDA PMID:24165938 Extracellular cell wall Ξ²(1,3)glucan is required to couple s... | MODIFY | Summary: Bgs4 is responsible for the major membrane beta(1,3)-glucan synthase activity and the cell wall branched beta-glucan (Munoz et al. 2013). Reason: The activity claim is sound and core. The paper attributes to Bgs4 both the major GS activity and the branched beta(1,3)glucan (B-BG), so the specific child GO:0140752, which the gene carries, is the better term. The branched-product assignment rests on the composition of the walls of bgs4 mutants and on Bgs4 carrying most membrane GS activity, not on a reconstituted enzyme; whether Bgs4 itself makes the beta-1,6 branch points, or relies on a partner remodeler as Bgs3 relies on Ghs2, is open (Ghs2 does not co-immunoprecipitate with Bgs4). Proposed replacements: branched 1,3-beta-D-glucan synthase activity Supporting Evidence: PMID:24165938 Bgs4 is responsible for the cell wall B-BG synthesis and the major Ξ²(1,3)GS activity. PMID:24165938 The essential protein Bgs4 synthesizes the main cell wall Ξ²(1,3)glucan. |
| GO:0003843 1,3-beta-D-glucan synthase activity | IEA GO_REF:0000120 | MODIFY | Summary: Combined automated annotation (InterPro GT48 domain, Rhea 21476, EC 2.4.1.34) for 1,3-beta-glucan synthase activity. Reason: Same claim as the IBA row. Correct but general; refined to GO:0140752, which the gene carries. The branched-product assignment rests on the composition of the walls of bgs4 mutants and on Bgs4 carrying most membrane GS activity, not on a reconstituted enzyme; whether Bgs4 itself makes the beta-1,6 branch points, or relies on a partner remodeler as Bgs3 relies on Ghs2, is open (Ghs2 does not co-immunoprecipitate with Bgs4). Proposed replacements: branched 1,3-beta-D-glucan synthase activity Supporting Evidence: file:SCHPO/bgs4/bgs4-uniprot.txt SIMILARITY: Belongs to the glycosyltransferase 48 family. PMID:34959732 It synthesizes the branched Ξ²(1,3)-D-glucan and is responsible for most GS activity |
| GO:0003843 1,3-beta-D-glucan synthase activity | IMP PMID:15615781 The novel fission yeast (1,3)beta-D-glucan synthase catalyti... | MODIFY | Summary: The cwg1-1 allele of bgs4 reduces cell wall beta-glucan and in vitro GS activity (Cortes et al. 2005). Reason: Abstract-only cache; the abstract states the reduced GS catalytic activity of cwg1-1. Correct and core, but refined to the branched child GO:0140752 used for Bgs4. The branched-product assignment rests on the composition of the walls of bgs4 mutants and on Bgs4 carrying most membrane GS activity, not on a reconstituted enzyme; whether Bgs4 itself makes the beta-1,6 branch points, or relies on a partner remodeler as Bgs3 relies on Ghs2, is open (Ghs2 does not co-immunoprecipitate with Bgs4). Proposed replacements: branched 1,3-beta-D-glucan synthase activity Supporting Evidence: PMID:15615781 cwg1-1 shows reduced cell-wall beta-glucan and GS catalytic activity PMID:34959732 It synthesizes the branched Ξ²(1,3)-D-glucan and is responsible for most GS activity |
| GO:0005737 cytoplasm | HDA PMID:16823372 ORFeome cloning and global analysis of protein localization ... | MARK AS OVER ANNOTATED | Summary: Genome-wide YFP ORFeome localization screen (Matsuyama et al. 2006) scoring Bgs4 as cytoplasmic. Reason: Bgs4 is a 16-TM plasma membrane synthase that acts at tips and septum. A cytoplasmic call for an overexpressed C-terminally tagged protein in a high-throughput screen most likely reflects secretory/endosomal transit (Bgs4 cycles through the Golgi between tips and septum). The observation is not removed, but is_active_in cytoplasm is not where the enzyme works. Supporting Evidence: file:SCHPO/bgs4/bgs4-uniprot.txt SUBCELLULAR LOCATION: Cell membrane {ECO:0000269|PubMed:15615781}; PMID:25977474 Cells without Rga7p moved Bgs4p normally from the poles to the Golgi complex near to the cell center |
| GO:0005794 Golgi apparatus | IDA PMID:25977474 A role for F-BAR protein Rga7p during cytokinesis in S. pomb... | KEEP AS NON CORE | Summary: Bgs4 moves from the poles to late Golgi compartments near the cell center before delivery to the cleavage site (Arasada and Pollard 2015). Reason: Direct imaging evidence for a Golgi location, which under the root-organelle policy is kept. The Golgi is a transit compartment in Bgs4 recycling from poles to the division site, not where the synthase acts, so it is non-core. Supporting Evidence: PMID:25977474 Cells without Rga7p moved Bgs4p normally from the poles to the Golgi complex near to the cell center PMID:25977474 does participate in the transport of a Ξ²-glucan synthetase (Bgs4p) from the late Golgi compartments to plasma membrane that is adjacent to the contractile ring |
| GO:0005886 plasma membrane | EXP PMID:15615781 The novel fission yeast (1,3)beta-D-glucan synthase catalyti... | ACCEPT | Summary: Plasma membrane localization of Bgs4 (Cortes et al. 2005), the source of UniProt experimental Cell membrane assignment. Reason: Bgs4 is an integral plasma membrane protein with 16 predicted TM helices that extrudes glucan into the wall; this is where the core activity happens. Supporting Evidence: file:SCHPO/bgs4/bgs4-uniprot.txt SUBCELLULAR LOCATION: Cell membrane {ECO:0000269|PubMed:15615781}; file:SCHPO/bgs4/bgs4-uniprot.txt TRANSMEM 519..539 |
| GO:0005886 plasma membrane | IBA GO_REF:0000033 | ACCEPT | Summary: PAINT IBA for plasma membrane at the fungal FKS node (sources S. cerevisiae Fks1, C. albicans Gsc1, S. pombe Bgs1 and Bgs4). Reason: FKS synthases are integral plasma membrane proteins. Bgs4 itself is among the experimental sources, which is the expected grounding, not circularity. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000787437 SUPPORTS TRANSFER FKS node; plasma membrane location is ancestral and directly observed for Bgs4. Supporting Evidence: file:SCHPO/bgs4/bgs4-uniprot.txt SUBCELLULAR LOCATION: Cell membrane {ECO:0000269|PubMed:15615781}; PMID:29930085 Interestingly, during PORTLI growth, Bgs4 appears as transient and mobile patches on the plasma membrane instead of being distributed homogeneously. |
| GO:0005886 plasma membrane | IEA GO_REF:0000044 | ACCEPT | Summary: UniProt subcellular location mapping (Cell membrane, SL-0039) to plasma membrane. Reason: The UniProt location is experimental (PubMed:15615781) and correct. Supporting Evidence: file:SCHPO/bgs4/bgs4-uniprot.txt SUBCELLULAR LOCATION: Cell membrane {ECO:0000269|PubMed:15615781}; |
| GO:0006075 (1->3)-beta-D-glucan biosynthetic process | IBA GO_REF:0000033 | MODIFY | Summary: PAINT IBA for (1->3)-beta-D-glucan biosynthesis at the fungal FKS node. Reason: Correct but general. Bgs4 makes the major cell wall branched (1->3)-beta-D-glucan, and the gene already carries the descendant GO:0071970 (IMP, three papers). Propagation Review Root cause: NO FAILURE CORE Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN001272353 SUPPORTS TRANSFER Fungal FKS node; beta-1,3-glucan synthesis is ancestral and Bgs4 is a full-length member. MODIFY only refines to the fungal cell wall descendant. Proposed replacements: fungal-type cell wall (1->3)-beta-D-glucan biosynthetic process Supporting Evidence: PMID:24165938 The essential protein Bgs4 synthesizes the main cell wall Ξ²(1,3)glucan. PMID:42786154 The biosynthesis of linear Ξ²β1,3-glucans is carried out by the essential integral membrane synthases Bgs1, Bgs3 and Bgs4 as well as the meiosis-specific Bgs2 |
| GO:0006075 (1->3)-beta-D-glucan biosynthetic process | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from the GT48 domain to (1->3)-beta-D-glucan biosynthesis. Reason: Correct but general. Bgs4 makes the major cell wall branched (1->3)-beta-D-glucan, and the gene already carries the descendant GO:0071970 (IMP, three papers). Proposed replacements: fungal-type cell wall (1->3)-beta-D-glucan biosynthetic process Supporting Evidence: file:SCHPO/bgs4/bgs4-uniprot.txt InterPro; IPR003440; Glyco_trans_48_dom. PMID:24165938 The essential protein Bgs4 synthesizes the main cell wall Ξ²(1,3)glucan. |
| GO:0016020 membrane | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping from the GT48 domain to membrane. Reason: Correct but general; the membrane is the plasma membrane, which the gene carries by EXP, IBA and IEA. Proposed replacements: plasma membrane Supporting Evidence: file:SCHPO/bgs4/bgs4-uniprot.txt SUBCELLULAR LOCATION: Cell membrane {ECO:0000269|PubMed:15615781}; file:SCHPO/bgs4/bgs4-uniprot.txt TRANSMEM 519..539 |
| GO:0030427 site of polarized growth | IDA PMID:15615781 The novel fission yeast (1,3)beta-D-glucan synthase catalyti... | ACCEPT | Summary: Bgs4 localizes to growing ends, septum, mating projections, and sites of wall synthesis during sexual differentiation and spore germination. Reason: The abstract documents localization at all sites of wall growth across the life cycle, for which the general term is the right level; specific tip and division-site rows complement it. Supporting Evidence: PMID:15615781 Bgs4p localizes to the growing ends, the medial ring and septum, and at each stage of wall synthesis or remodeling that occurs during sexual differentiation |
| GO:0030428 cell septum | EXP PMID:15615781 The novel fission yeast (1,3)beta-D-glucan synthase catalyti... | MODIFY | Summary: Bgs4 at the cell septum (Cortes et al. 2005). Reason: Correct but general. The septum Bgs4 builds is the cytokinetic division septum, and the gene already carries the descendant GO:0000935 division septum (IDA, same paper). Proposed replacements: division septum Supporting Evidence: file:SCHPO/bgs4/bgs4-uniprot.txt Cell septum {ECO:0000269|PubMed:15615781}. Spore wall {ECO:0000269|PubMed:15615781}. file:SCHPO/bgs4/bgs4-uniprot.txt Following nuclear division and formation of the contractile ring, relocalizes from the cell ends to the assembling division septum. |
| GO:0030428 cell septum | IEA GO_REF:0000044 | MODIFY | Summary: UniProt subcellular location mapping (Cell septum, SL-0455). Reason: Correct but general. The septum Bgs4 builds is the cytokinetic division septum, and the gene already carries the descendant GO:0000935 division septum (IDA, same paper). Proposed replacements: division septum Supporting Evidence: file:SCHPO/bgs4/bgs4-uniprot.txt Cell septum {ECO:0000269|PubMed:15615781}. Spore wall {ECO:0000269|PubMed:15615781}. file:SCHPO/bgs4/bgs4-uniprot.txt Following nuclear division and formation of the contractile ring, relocalizes from the cell ends to the assembling division septum. |
| GO:0031160 spore wall | EXP PMID:15615781 The novel fission yeast (1,3)beta-D-glucan synthase catalyti... | KEEP AS NON CORE | Summary: Bgs4 at forming spore walls (Cortes et al. 2005). Reason: Bgs4 decorates the forming spore walls and is needed for spore germination, but spore wall maturation is mainly Bgs2-dependent, and imaging cannot resolve the forespore membrane from the wall. Kept as a correct, peripheral location. Supporting Evidence: file:SCHPO/bgs4/bgs4-uniprot.txt During sexual development, localizes to the mating projection, the contact region at the cell-cell fusion site, and to the forming spore walls. PMID:15615781 Bgs4p localizes to the growing ends, the medial ring and septum, and at each stage of wall synthesis or remodeling that occurs during sexual differentiation |
| GO:0031160 spore wall | IEA GO_REF:0000044 | KEEP AS NON CORE | Summary: UniProt subcellular location mapping (Spore wall, SL-0254). Reason: Bgs4 decorates the forming spore walls and is needed for spore germination, but spore wall maturation is mainly Bgs2-dependent, and imaging cannot resolve the forespore membrane from the wall. Kept as a correct, peripheral location. Supporting Evidence: file:SCHPO/bgs4/bgs4-uniprot.txt During sexual development, localizes to the mating projection, the contact region at the cell-cell fusion site, and to the forming spore walls. PMID:15615781 Bgs4p localizes to the growing ends, the medial ring and septum, and at each stage of wall synthesis or remodeling that occurs during sexual differentiation |
| GO:0031520 plasma membrane of cell tip | IDA PMID:24165938 Extracellular cell wall Ξ²(1,3)glucan is required to couple s... | ACCEPT | Summary: GFP-Bgs4 at the plasma membrane of the cell tips (Munoz et al. 2013). Reason: Bgs4 at the tip plasma membrane builds the polar wall; Bgs4 depletion thins the tip wall and causes lysis there. This is a precise core location. Supporting Evidence: PMID:24165938 Bgs4 absence generates a thin cell wall (red arrow) in both new end (close to FS) and OE. PMID:29930085 Interestingly, during PORTLI growth, Bgs4 appears as transient and mobile patches on the plasma membrane instead of being distributed homogeneously. |
| GO:0032153 cell division site | IDA PMID:26702831 Oligomerization but Not Membrane Bending Underlies the Funct... | ACCEPT | Summary: Bgs4 at the cell division site, used as a septum marker in a cytokinesis/trafficking study. Reason: Only the abstract is cached and it does not mention Bgs4, so this defers to the curator. Division-site localization is independently shown by Cortes et al. 2005 and Arasada and Pollard 2015, and it is where Bgs4 builds the septum, so it is a core location. Supporting Evidence: file:SCHPO/bgs4/bgs4-uniprot.txt Following nuclear division and formation of the contractile ring, relocalizes from the cell ends to the assembling division septum. PMID:25977474 does participate in the transport of a Ξ²-glucan synthetase (Bgs4p) from the late Golgi compartments to plasma membrane that is adjacent to the contractile ring |
| GO:0032153 cell division site | IDA PMID:27974503 Traffic Through the Trans-Golgi Network and the Endosomal Sy... | ACCEPT | Summary: Bgs4 at the cell division site, used as a septum marker in a cytokinesis/trafficking study. Reason: Only the abstract is cached and it does not mention Bgs4, so this defers to the curator. Division-site localization is independently shown by Cortes et al. 2005 and Arasada and Pollard 2015, and it is where Bgs4 builds the septum, so it is a core location. Supporting Evidence: file:SCHPO/bgs4/bgs4-uniprot.txt Following nuclear division and formation of the contractile ring, relocalizes from the cell ends to the assembling division septum. PMID:25977474 does participate in the transport of a Ξ²-glucan synthetase (Bgs4p) from the late Golgi compartments to plasma membrane that is adjacent to the contractile ring |
| GO:0032154 cleavage furrow | IDA PMID:25977474 A role for F-BAR protein Rga7p during cytokinesis in S. pomb... | ACCEPT | Summary: Bgs4 delivered from late Golgi to the plasma membrane adjacent to the contractile ring (Arasada and Pollard 2015). Reason: The cleavage furrow is the ingressing plasma membrane at the division site, an accurate description of where Bgs4 sits while it builds the septum. Late or reduced Bgs4 delivery there causes septal defects and lysis. Supporting Evidence: PMID:25977474 does participate in the transport of a Ξ²-glucan synthetase (Bgs4p) from the late Golgi compartments to plasma membrane that is adjacent to the contractile ring |
| GO:0035841 new growing cell tip | IDA PMID:24165938 Extracellular cell wall Ξ²(1,3)glucan is required to couple s... | KEEP AS NON CORE | Summary: Bgs4 at the new growing end (Munoz et al. 2013). Reason: Accurate and as precise as the evidence, but a subset of the cell tip location; the core location is the cell tip plasma membrane. Supporting Evidence: PMID:24165938 Bgs4 absence generates a thin cell wall (red arrow) in both new end (close to FS) and OE. |
| GO:0043332 mating projection tip | IDA PMID:25825517 A formin-nucleated actin aster concentrates cell wall hydrol... | KEEP AS NON CORE | Summary: Bgs4-GFP decorates the whole shmoo tip during mating, unlike the focalized glucanases (Dudin et al. 2015). Reason: Full text cached and supports the localization. It reflects Bgs4 at a site of polarized wall growth during sexual differentiation, peripheral to the vegetative core role. Supporting Evidence: PMID:25825517 the cell wall synthases Bgs1 and Bgs4 do not concentrate at the fusion focus but rather decorate the entire shmoo tip throughout the fusion process |
| GO:0051278 fungal-type cell wall polysaccharide biosynthetic process | IBA GO_REF:0000033 | MODIFY | Summary: PAINT IBA for fungal-type cell wall polysaccharide biosynthesis at the fungal FKS node. Reason: Correct but general. The polysaccharide is (1->3)-beta-D-glucan, and the gene already carries the descendant GO:0071970. Propagation Review Root cause: NO FAILURE CORE Failure modes: GRANULARITY MISMATCH Sources checked: PANTHER:PTN001272353 SUPPORTS TRANSFER Fungal FKS node; Bgs4 is a full-length member. MODIFY only refines to the cell wall (1->3)-beta-D-glucan descendant. Proposed replacements: fungal-type cell wall (1->3)-beta-D-glucan biosynthetic process Supporting Evidence: PMID:24165938 The essential protein Bgs4 synthesizes the main cell wall Ξ²(1,3)glucan. |
| GO:0051286 cell tip | IDA PMID:15615781 The novel fission yeast (1,3)beta-D-glucan synthase catalyti... | ACCEPT | Summary: Bgs4 at the growing cell ends (Cortes et al. 2005). Reason: Core location for polarized wall growth; lysis occurs at growing poles on bgs4 shut-off. Supporting Evidence: PMID:15615781 Bgs4p localizes to the growing ends, the medial ring and septum, and at each stage of wall synthesis or remodeling that occurs during sexual differentiation |
| GO:0051286 cell tip | IDA PMID:20870879 Reorganization of the growth pattern of Schizosaccharomyces ... | ACCEPT | Summary: Bgs4 concentrated at the growing tip of invasive filament cells (Dodgson et al. 2010). Reason: Full text cached; Bgs4 tracks the growing tip. Consistent core location. Supporting Evidence: PMID:20870879 comprising Spo20, Bgs4, activated Cdc42, and Crn1, are all concentrated at the growing tip |
| GO:0051286 cell tip | IDA PMID:25977474 A role for F-BAR protein Rga7p during cytokinesis in S. pomb... | ACCEPT | Summary: Bgs4 at the poles before its relocation to the division site (Arasada and Pollard 2015). Reason: Consistent with the other cell tip rows. Supporting Evidence: PMID:25977474 Cells without Rga7p moved Bgs4p normally from the poles to the Golgi complex near to the cell center |
| GO:0051286 cell tip | IDA PMID:27974503 Traffic Through the Trans-Golgi Network and the Endosomal Sy... | ACCEPT | Summary: Bgs4 at cell tips in an exomer/clathrin adaptor trafficking study (Hoya et al. 2017). Reason: Abstract-only and does not name Bgs4; defers to the curator. Tip localization is independently established. Supporting Evidence: PMID:15615781 Bgs4p localizes to the growing ends, the medial ring and septum, and at each stage of wall synthesis or remodeling that occurs during sexual differentiation PMID:29930085 In control 3-BrB-PP1-treated cells, mCherry-Bgs4 remained highly polarized at cell tips, and cells grew in a polarized manner. |
| GO:0071970 fungal-type cell wall (1->3)-beta-D-glucan biosynthetic process | IMP PMID:15615781 The novel fission yeast (1,3)beta-D-glucan synthase catalyti... | ACCEPT | Summary: bgs4 mutants (cwg1-1) have reduced cell wall beta-glucan; shut-off causes lysis at poles and septum. Reason: The most specific accurate process term for Bgs4 core role: synthesis of the main cell wall branched beta-1,3-glucan. Supporting Evidence: PMID:15615781 cwg1-1 shows reduced cell-wall beta-glucan and GS catalytic activity PMID:24165938 The essential protein Bgs4 synthesizes the main cell wall Ξ²(1,3)glucan. |
| GO:0071970 fungal-type cell wall (1->3)-beta-D-glucan biosynthetic process | IMP PMID:24165938 Extracellular cell wall Ξ²(1,3)glucan is required to couple s... | ACCEPT | Summary: Bgs4-derived beta(1,3)glucan is the main cell wall glucan; its loss thins the wall (Munoz et al. 2013). Reason: Full text supports the IMP; core process. Supporting Evidence: PMID:24165938 The essential protein Bgs4 synthesizes the main cell wall Ξ²(1,3)glucan. PMID:24165938 Bgs4 is responsible for the cell wall B-BG synthesis and the major Ξ²(1,3)GS activity. |
| GO:0071970 fungal-type cell wall (1->3)-beta-D-glucan biosynthetic process | IMP PMID:7592316 Papulacandin B resistance in budding and fission yeasts: iso... | ACCEPT | Summary: pbr1 (papulacandin B resistant) mutants, later shown to be bgs4 alleles, alter the sensitivity of the membrane (1,3)beta-D-glucan synthase to papulacandin B. Reason: Abstract-only; the abstract shows pbr1 mutations change the particulate (catalytic) fraction of the GS enzyme. pbr1-8 is a point mutation in bgs4 (PMID:34959732). Defer to the curator; consistent with the other IMP rows. Supporting Evidence: PMID:7592316 Detergent dissociation of the S. pombe synthase into soluble and particulate fractions and subsequent reconstitution indicated that the resistance character of pbr1 mutants resides in the particulate fraction of the enzyme. PMID:34959732 These two mutants are exclusively due to point mutations in the bgs4+ sequence. |
| GO:0110085 mitotic actomyosin contractile ring | IDA PMID:29930085 Local and global Cdc42 guanine nucleotide exchange factors f... | MODIFY | Summary: IDA for Bgs4 at the cytokinetic ring from a Cdc42 GEF polarity study (PMID:29930085). The cached text contains no statement about Bgs4 at the ring, so the basis of the row could not be located; the correction below rests on Bgs4's membrane topology. Reason: Bgs4 is an integral plasma membrane synthase, not a component of the actomyosin cytoskeletal ring; it is delivered to the plasma membrane adjacent to the ring and colocalizes with it at light-microscopy resolution. The essence (Bgs4 at the ring site) is right; the accurate term is cleavage furrow, which the gene already carries (IDA, PMID:25977474). Proposed replacements: cleavage furrow Supporting Evidence: PMID:25977474 does participate in the transport of a Ξ²-glucan synthetase (Bgs4p) from the late Golgi compartments to plasma membrane that is adjacent to the contractile ring PMID:15615781 Bgs4p localizes to the growing ends, the medial ring and septum, and at each stage of wall synthesis or remodeling that occurs during sexual differentiation |
| GO:0140752 branched 1,3-beta-D-glucan synthase activity | TAS PMID:34959732 Echinocandin Drugs Induce Differential Effects in Cytokinesi... | ACCEPT | Summary: Bgs4 synthesizes the branched beta(1,3)-D-glucan and accounts for most GS activity (Martins et al. 2022). Reason: The most specific MF term; PomBase defined GO:0140752 with this paper and uses it for Bgs4 in its GO-CAM for septum assembly. Bgs4 is the major GS activity and is required for the major branched beta-1,3-glucan of the wall. The branched-product assignment rests on the composition of the walls of bgs4 mutants and on Bgs4 carrying most membrane GS activity, not on a reconstituted enzyme; whether Bgs4 itself makes the beta-1,6 branch points, or relies on a partner remodeler as Bgs3 relies on Ghs2, is open (Ghs2 does not co-immunoprecipitate with Bgs4). Supporting Evidence: PMID:34959732 It synthesizes the branched Ξ²(1,3)-D-glucan and is responsible for most GS activity PMID:24165938 Bgs4 is responsible for the cell wall B-BG synthesis and the major Ξ²(1,3)GS activity. PMID:34959732 The branched Ξ²(1,3)-D-glucan produced by Bgs4 is vital for maintaining cell shape and septum formation and completion. |
| GO:1902716 cell cortex of growing cell tip | IDA PMID:29930085 Local and global Cdc42 guanine nucleotide exchange factors f... | MODIFY | Summary: mCherry-Bgs4 at growing cell tips used as a polarity marker (Cdc42 GEF study). Reason: Full text cached. The paper describes Bgs4 on the plasma membrane at tips. Bgs4 is an integral membrane protein, not a cortical (sub-membrane) protein, so the accurate term is plasma membrane of cell tip, which the gene already carries. Proposed replacements: plasma membrane of cell tip Supporting Evidence: PMID:29930085 In control 3-BrB-PP1-treated cells, mCherry-Bgs4 remained highly polarized at cell tips, and cells grew in a polarized manner. PMID:29930085 Interestingly, during PORTLI growth, Bgs4 appears as transient and mobile patches on the plasma membrane instead of being distributed homogeneously. |
| GO:1990344 secondary cell septum biogenesis | IMP PMID:24165938 Extracellular cell wall Ξ²(1,3)glucan is required to couple s... | ACCEPT | Summary: Without Bgs4 the septum completely lacks the secondary septum (Munoz et al. 2013). Reason: Full text cached and directly supports it. Bgs4 synthesizes the branched glucan that forms the secondary septum; this is a core process, also used for Bgs4 in the PomBase GO-CAM. Supporting Evidence: PMID:24165938 Bgs4 absence causes the total absence of SS. PMID:24165938 Bgs4-derived Ξ²(1,3)glucan is essential for secondary septum formation and correct primary septum completion. |
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Download this section (compressed HTML)Q: Does Bgs4 itself introduce the beta-1,6 branch points of the major cell wall branched beta-1,3-glucan, or does a partner remodeler do so, as Ghs2 is proposed to do for Bgs3? Ghs2 does not bind Bgs4 (PMID:42786154), so any Bgs4 partner is unidentified.
Q: Should GO keep GO:0140752 branched 1,3-beta-D-glucan synthase activity as a catalytic activity of the synthase, given that FKS enzymes are thought to extrude linear chains and the branched assignment rests on wall composition of bgs4 mutants rather than on a reconstituted enzyme?
Q: How does Rho1 (via the GEFs Rgf1-3) regulate Bgs4 differently at the cell tips and at the septum, and what targets Bgs4 to the septum only after Bgs1 and septum initiation?
Experiment: Purify or reconstitute Bgs4 with Rho1-GTP in proteoliposomes, feed UDP-[13C]glucose, and determine the linkage composition of the product (methylation analysis or solid-state NMR) to test whether Bgs4 alone makes branched or linear beta-1,3-glucan.
Experiment: Proteomic search for Bgs4 partners (affinity purification of functional GFP-Bgs4 from membranes, or proximity labelling) to find a GH16/GH72-type transglycosylase that could branch the Bgs4 product, analogous to Ghs2 for Bgs3.
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