Puc1 is the Cln-type (G1) cyclin of the fission yeast Schizosaccharomyces pombe. It has no catalytic activity of its own: it binds the single cell-cycle cyclin-dependent kinase Cdc2 and generates a Puc1-Cdc2 kinase that, unlike the Cdc13-Cdc2 and Cig2-Cdc2 complexes, is largely resistant to the G1 CDK inhibitor Rum1 and can phosphorylate Rum1 on the residues (Thr58/Thr62) that target it for SCF-dependent destruction. Through this Rum1-directed activity Puc1 helps open the G1 gate: redundantly with the B-type cyclins Cig1 and Cig2 it shortens G1 and couples entry into S phase to cell size, so that puc1 deletion alone is nearly silent whereas cig1 cig2 puc1 cells have a long G1, enter S phase at a larger size and arrest in G1 after fewer divisions when nitrogen is withdrawn. Puc1 cannot itself drive DNA replication, which requires the B-type cyclin-Cdc2 complexes; its role is to relieve G1 inhibition. puc1+ was discovered by its ability to complement budding-yeast cells lacking the G1 cyclins CLN1, CLN2 and CLN3, and the Puc1 cyclin associates in vivo with the Ran1/Pat1 kinase and with Cdc10, the DNA-binding subunit of the MBF Start transcription factor, under Ran1 control. Puc1 also governs the choice between continued proliferation and sexual differentiation: its transcript rises on nitrogen starvation while the protein is held down post-transcriptionally by the RNA-binding protein Zfs1, and Puc1 levels set, in a dose-dependent way, how readily cells exit the mitotic cycle to mate - overexpression blocks sexual development and rescues the lethal meiosis of pat1ts cells, while loss of puc1 restores mating to zfs1 mutants and accelerates G1 arrest under nitrogen limitation. Puc1 is non-essential, is nearly undetectable during meiotic prophase and has no specific meiotic function. Localization data come only from a proteome-wide YFP screen, which placed Puc1 in the nucleus and cytosol.
| GO Term | Evidence | Action | Reason |
|---|---|---|---|
| GO:0000082 G1/S transition of mitotic cell cycle | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic (PAINT) annotation of G1/S transition of the mitotic cell cycle from the G1-cyclin node PTN000019791 (cyclin D, Cln1/2/3, Cig1/Cig2, Puc1). Puc1 is the fission-yeast Cln-type cyclin: it complements budding-yeast cln1 cln2 cln3 deficiency, and in S. pombe the Puc1-Cdc2 kinase phosphorylates the CDK inhibitor Rum1 and, redundantly with Cig1 and Cig2, sets the length of G1 and the cell size at which S phase begins. Reason: The node placement is sound - promoting the G1/S transition is the ancestral function of the Cln/cyclin-D clade - and the target has its own direct support: complementation of G1-arrested cln- budding yeast (PMID:1828291), Puc1-Cdc2 phosphorylation of Rum1 with a marked G1 delay and increased size at S-phase entry in cig1 cig2 puc1 cells (Martin-Castellanos et al. 2000, cited via the deep-research file), and the Ran1/Cdc10 association at Start (PMID:9201720). Core function, although executed redundantly with Cig1/Cig2. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000019791 · PTN000019791 SUPPORTS TRANSFER G1-cyclin ancestral node; Puc1 is inside the Cln-like clade and has target-specific genetic and biochemical G1/S evidence. Supporting Evidence: PMID:1828291 We have isolated a G1-type cyclin gene called puc1+ from S. pombe, using a functional assay in S. cerevisiae file:SCHPO/puc1/puc1-deep-research-falcon.md The principal biological role of Puc1 is to promote progression through G1 and help couple Start/S-phase entry to cell size. file:SCHPO/puc1/puc1-deep-research-falcon.md Puc1 and Cdc2 immunocomplexes phosphorylated Rum1 in vitro at Thr58 and Thr62. PMID:30640914 Cig1, Cig2 and Puc1 cyclins control G1 progression, meanwhile Cdc13 is essential to promote chromosome segregations |
| GO:0000307 cyclin-dependent protein kinase holoenzyme complex | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic annotation placing Puc1 in a cyclin-dependent protein kinase holoenzyme complex. Puc1 is a non-catalytic cyclin that binds the single fission-yeast cell-cycle CDK Cdc2; Puc1 immunocomplexes carry Cdc2-dependent histone H1 and Rum1 kinase activity that, unlike Cdc13-Cdc2 and Cig2-Cdc2, is resistant to Rum1 inhibition. Reason: Being the regulatory subunit of a cyclin-CDK holoenzyme is the family-wide property behind this node, and it is directly demonstrated for Puc1 by the Puc1-Cdc2 kinase assays of Martin-Castellanos et al. 2000 (cited via the deep-research file) and by the in vivo Puc1 complexes of Caligiuri et al. 1997. Core. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000019791 · PTN000019791 SUPPORTS TRANSFER Cyclin-CDK holoenzyme membership is family-wide; the Puc1-Cdc2 kinase has been assayed directly. Supporting Evidence: file:SCHPO/puc1/puc1-deep-research-falcon.md At 10 nM Rum1, Cdc2–Cdc13 activity was inhibited and Cdc2–Cig2 activity was almost completely inhibited, whereas Puc1-associated activity was not significantly inhibited. file:SCHPO/puc1/puc1-deep-research-falcon.md Puc1 and Cdc2 immunocomplexes phosphorylated Rum1 in vitro at Thr58 and Thr62. PMID:9201720 We demonstrate that the Puc1 cyclin associates with Ran1 and Cdc10 in vivo and that the Ran1 protein kinase functions to control the association between Puc1 and Cdc10 |
| GO:0005634 nucleus | HDA PMID:16823372 ORFeome cloning and global analysis of protein localization ... | ACCEPT | Summary: High-throughput localization from the Matsuyama et al. 2006 ORFeome YFP screen (about 90% of the proteome imaged); PomBase recorded Puc1-YFP in the nucleus (and cytosol, separate row). The record is abstract-only, so the Puc1 image itself cannot be inspected here. Reason: Consistent with the nuclear location of the known Puc1-Cdc2 targets and partners (Rum1, the MBF subunit Cdc10, Ste11) and with the IBA nucleus row; the nucleus is where the G1 cyclin-CDK acts on Start and on the differentiation decision. Core location, with the caveat that no targeted localization study of endogenous Puc1 exists. Supporting Evidence: PMID:16823372 we determined the localization of 4,431 proteins, corresponding to approximately 90% of the fission yeast proteome, by tagging each ORF with the yellow fluorescent protein PMID:9201720 We demonstrate that the Puc1 cyclin associates with Ran1 and Cdc10 in vivo and that the Ran1 protein kinase functions to control the association between Puc1 and Cdc10 file:SCHPO/puc1/puc1-deep-research-falcon.md The retrieved Puc1-specific studies do **not** establish a definitive localization by direct microscopy or fractionation. |
| GO:0005634 nucleus | IBA GO_REF:0000033 | ACCEPT | Summary: Phylogenetic annotation that Puc1 is active in the nucleus, from node PTN000019791 with cyclins from plants, animals and fungi as donors. Puc1-YFP was scored nuclear in the ORFeome screen and the substrates of the Puc1-Cdc2 kinase (Rum1, and via Ran1 the MBF subunit Cdc10) are nuclear proteins. Reason: Concordant with the HDA nucleus row and with the nuclear site of the core G1/S function; sound propagation. Propagation Review Root cause: NO FAILURE CORE Sources checked: PANTHER:PTN000019791 · PTN000019791 SUPPORTS TRANSFER Nuclear site of action of cyclin-CDKs is ancestral and corroborated for Puc1 by the ORFeome screen. Supporting Evidence: PMID:16823372 we determined the localization of 4,431 proteins, corresponding to approximately 90% of the fission yeast proteome, by tagging each ORF with the yellow fluorescent protein PMID:9201720 We demonstrate that the Puc1 cyclin associates with Ran1 and Cdc10 in vivo and that the Ran1 protein kinase functions to control the association between Puc1 and Cdc10 |
| GO:0005737 cytoplasm | IBA GO_REF:0000033 | KEEP AS NON CORE | Summary: Phylogenetic annotation that Puc1 is active in the cytoplasm, propagated from the cyclin node whose donors include cyclins with genuine cytoplasmic functions (Cln1/Cln2, cyclin D, mitotic B-type cyclins). For Puc1 the ORFeome screen also recorded a cytosolic signal (HDA row below), so a cytoplasmic pool is documented; but no cytoplasm-specific Puc1-Cdc2 activity has been described and its known targets are nuclear. Reason: Not wrong as a location (target-specific HDA cytosol data exist), but the functional site of the G1 cyclin is the nucleus, where Rum1, Cdc10/MBF and Ste11 are phosphorylated; graded non-core rather than a core site of activity, in line with the treatment of the same propagation for the fission-yeast cig2 and budding-yeast Cln3 reviews. Propagation Review Root cause: NO FAILURE NON CORE Sources checked: PANTHER:PTN000019791 · PTN000019791 SUPPORTS TRANSFER Cytoplasmic pool is corroborated by the ORFeome screen for Puc1 itself, but no cytoplasmic function of Puc1-Cdc2 is known. Supporting Evidence: PMID:16823372 we determined the localization of 4,431 proteins, corresponding to approximately 90% of the fission yeast proteome, by tagging each ORF with the yellow fluorescent protein file:SCHPO/puc1/puc1-deep-research-falcon.md The retrieved Puc1-specific studies do **not** establish a definitive localization by direct microscopy or fractionation. |
| GO:0005829 cytosol | HDA PMID:16823372 ORFeome cloning and global analysis of protein localization ... | KEEP AS NON CORE | Summary: High-throughput ORFeome YFP localization: PomBase recorded Puc1-YFP in the cytosol as well as the nucleus. Abstract-only record. Reason: A documented but functionally uncharacterised pool: cyclins are synthesised in the cytosol and Cln-type cyclins often show diffuse signal, but every characterised Puc1-Cdc2 output (Rum1 phosphorylation, Cdc10/MBF association, restraint of Ste11-driven differentiation) is nuclear. Retained as a non-core location. Supporting Evidence: PMID:16823372 we determined the localization of 4,431 proteins, corresponding to approximately 90% of the fission yeast proteome, by tagging each ORF with the yellow fluorescent protein |
| GO:0016538 cyclin-dependent protein serine/threonine kinase regulator activity | IBA GO_REF:0000033 | MODIFY | Summary: Phylogenetic annotation of cyclin-dependent protein serine/threonine kinase regulator activity, the defining function of the cyclin family; puc1 (PomBase:SPBC19F5.01c) is itself among the experimental donors, as expected because PomBase carries the IGI row from Forsburg & Nurse 1991. Puc1 binds Cdc2 and confers on it a Rum1-resistant kinase activity that phosphorylates Rum1 T58/T62. Reason: The IBD node placement is sound - CDK-regulatory activity is ancestral to the whole cyclin family and Puc1 is inside the clade with its own evidence - but every member of node PTN000019791 is an activating cyclin (the node contains no CDK inhibitors), and for Puc1 specifically association with Cdc2 generates kinase activity (Martin-Castellanos et al. 2000) and Puc1 restores proliferation to cln-deficient budding yeast. The child term cyclin-dependent protein serine/threonine kinase activator activity (GO:0061575) is the accurate description; the parent 'regulator' term is not wrong, only less informative. Same refinement as applied in the budding-yeast CLN3 review. Propagation Review Root cause: TERM SCOPING PROBLEM Sources checked: PANTHER:PTN000019791 · PTN000019791 SUPPORTS TRANSFER Valid family-level transfer with target-specific grounding; the term is simply broader than the activator activity shared by all members of the node. Proposed replacements: cyclin-dependent protein serine/threonine kinase activator activity Supporting Evidence: file:SCHPO/puc1/puc1-deep-research-falcon.md Puc1 and Cdc2 immunocomplexes phosphorylated Rum1 in vitro at Thr58 and Thr62. file:SCHPO/puc1/puc1-deep-research-falcon.md At 10 nM Rum1, Cdc2–Cdc13 activity was inhibited and Cdc2–Cig2 activity was almost completely inhibited, whereas Puc1-associated activity was not significantly inhibited. PMID:1828291 We have isolated a G1-type cyclin gene called puc1+ from S. pombe, using a functional assay in S. cerevisiae |
| GO:0016538 cyclin-dependent protein serine/threonine kinase regulator activity | IEA GO_REF:0000117 | MODIFY | Summary: ARBA machine-learning annotation of CDK regulator activity derived from the cyclin family signature. Correct at family level and redundant with the IBA and IGI rows. Reason: The automated inference stops at the generic parent; the experimental evidence (Puc1-associated Cdc2 kinase activity toward histone H1 and Rum1, complementation of CLN loss) shows that Puc1 activates Cdc2, so the activator child term (GO:0061575) proposed on the IBA and IGI rows is the consistent replacement. Proposed replacements: cyclin-dependent protein serine/threonine kinase activator activity Supporting Evidence: file:SCHPO/puc1/puc1-deep-research-falcon.md At 10 nM Rum1, Cdc2–Cdc13 activity was inhibited and Cdc2–Cig2 activity was almost completely inhibited, whereas Puc1-associated activity was not significantly inhibited. file:SCHPO/puc1/puc1-deep-research-falcon.md Puc1 expression could rescue a budding-yeast background lacking CLN1, CLN2, and CLN3. |
| GO:0016538 cyclin-dependent protein serine/threonine kinase regulator activity | IGI PMID:1828291 Identification of a G1-type cyclin puc1+ in the fission yeas... | MODIFY | Summary: Genetic-interaction annotation (with S. cerevisiae CLN3, SGD:S000000038) from the paper that cloned puc1+ by complementation of budding-yeast G1-cyclin deficiency: puc1+ restores proliferation to cells lacking Cln function, i.e. it can supply the cyclin that activates Cdc28 at Start, and its expression in S. pombe gives a cyclin-like role distinct from the B-type mitotic cyclin. Reason: The complementation assay demonstrates that Puc1 can activate a CDK (Cdc28) whose G1 activity otherwise depends on Cln1/2/3, and in S. pombe Puc1-Cdc2 is an active, Rum1-resistant kinase. The evidence therefore supports the more specific child term cyclin-dependent protein serine/threonine kinase activator activity (GO:0061575) rather than the generic 'regulator' parent. The cached record is abstract-only; the curator's reading of the full text is not contested. Proposed replacements: cyclin-dependent protein serine/threonine kinase activator activity Supporting Evidence: PMID:1828291 We have isolated a G1-type cyclin gene called puc1+ from S. pombe, using a functional assay in S. cerevisiae PMID:1828291 At least one is required for progression through the G1-S phase, and deletion of all three leads to G1 arrest PMID:1828291 Expression of puc1+ in S. pombe indicates that it has a cyclin-like role in the fission yeast distinct from the role of the B-type mitotic cyclin file:SCHPO/puc1/puc1-deep-research-falcon.md Puc1 expression could rescue a budding-yeast background lacking CLN1, CLN2, and CLN3. |
| GO:0023052 signaling | NAS GO_REF:0000051 | MARK AS OVER ANNOTATED | Summary: PomBase keyword-mapping (NAS) annotation to the root-level term 'signaling'. Puc1 is a cyclin; its regulatory role in the nutrient-responsive decision between cycling and sexual differentiation is real, but it is executed as the activating subunit of the Cdc2 kinase, and GO already captures that with the specific G1/S-regulation and mitotic-to-meiotic switching terms on this gene. Reason: The term is not strictly false - Puc1 abundance integrates nitrogen/TOR input (via Zfs1) into the G1 decision - but 'signaling' at the root of the branch conveys no information about what Puc1 does, and the specific terms (GO:1900087, GO:0110045) are already annotated. A generic keyword mapping of this kind is an over-annotation rather than a function to retain. Supporting Evidence: PMID:29084823 We found that Zfs1 negatively regulates the G1 cyclin Puc1, and deregulated Puc1 levels inhibit differentiation in the zfs1Δ mutant PMID:8006074 We conclude that puc1 contributes to negative regulation of the timing of sexual development in fission yeast, and functions at the transition between cycling and non-cycling cells |
| GO:0044843 cell cycle G1/S phase transition | IEA GO_REF:0000117 | ACCEPT | Summary: ARBA electronic annotation to the generic 'cell cycle G1/S phase transition', the parent of the mitotic-specific term carried by the IBA row. Reason: Correct, if general: Puc1 functions at the mitotic G1/S transition redundantly with Cig1 and Cig2 (Martin-Castellanos et al. 2000) and the mitotic-specific child GO:0000082 is already annotated by IBA. Family-level electronic inferences may legitimately be broader than the experimental rows. Supporting Evidence: PMID:30640914 Cig1, Cig2 and Puc1 cyclins control G1 progression, meanwhile Cdc13 is essential to promote chromosome segregations file:SCHPO/puc1/puc1-deep-research-falcon.md The principal biological role of Puc1 is to promote progression through G1 and help couple Start/S-phase entry to cell size. |
| GO:0044843 cell cycle G1/S phase transition | IMP PMID:8006074 Analysis of the Schizosaccharomyces pombe cyclin puc1: evide... | ACCEPT | Summary: Mutant-phenotype annotation from Forsburg & Nurse 1994, the molecular characterisation of puc1. The abstract records that no puc1 function could be detected at the mitotic G1/S transition in otherwise wild-type cells, but that puc1 acts at the transition between cycling and non-cycling cells: puc1 expression rises in nitrogen starvation, puc1 affects the timing of sexual development, and puc1 overexpression blocks sexual development and rescues pat1ts lethal meiosis. The full text (not cached) documents the G1 behaviour of puc1 mutant and overexpressing cells on which PomBase based this IMP. Reason: The curator read the full text and the G1/S assignment is biologically correct for Puc1: its contribution to G1 progression is masked by Cig1/Cig2 in rich medium (which explains the negative result in the abstract) and becomes visible when nutrients decline or the other G1 cyclins are absent - Martin-Castellanos et al. 2000 later showed a marked G1 delay and increased size at S-phase entry in cig1 cig2 puc1 cells. The generic term is acceptable here because the paper's phenotype concerns whether cells make the G1/S decision at all rather than the mitotic transition machinery per se; the mitotic-specific term is carried by the IBA row. Not overruled from an abstract-only cache. Supporting Evidence: PMID:8006074 We fail to identify any function of this cyclin at the mitotic G1/S transition in S. pombe, but demonstrate that it does function in exit from the mitotic cycle PMID:8006074 Expression of the puc1+ gene is increased during nitrogen starvation, and puc1 affects the timing of sexual development in response to starvation PMID:29084823 although it functions redundantly with other cyclins in the fission yeast mitotic cell cycle (Martin-Castellanos et al., 2000), it has been suggested that it has a role in mitotic cycle exit (Forsburg and Nurse, 1994) file:SCHPO/puc1/puc1-deep-research-falcon.md The principal biological role of Puc1 is to promote progression through G1 and help couple Start/S-phase entry to cell size. |
| GO:0051726 regulation of cell cycle | IEA GO_REF:0000117 | MODIFY | Summary: ARBA electronic annotation to the very general 'regulation of cell cycle'. Puc1 regulates a specific transition, G1/S, in the positive direction, and this is already annotated experimentally. Reason: The mapping is correct but uninformative; the specific process is positive regulation of the G1/S transition of the mitotic cell cycle (GO:1900087), supported by the EXP row (PMID:9201720), the complementation of cln-deficient budding yeast (PMID:1828291) and the Rum1-directed kinase activity of Puc1-Cdc2 (Martin-Castellanos et al. 2000). Proposed replacements: positive regulation of G1/S transition of mitotic cell cycle Supporting Evidence: PMID:9201720 We demonstrate that the Puc1 cyclin associates with Ran1 and Cdc10 in vivo and that the Ran1 protein kinase functions to control the association between Puc1 and Cdc10 file:SCHPO/puc1/puc1-deep-research-falcon.md Accordingly, the favored mechanism is that Cdc2–Puc1 helps mark Rum1 for degradation near the end of G1. |
| GO:0110045 negative regulation of cell cycle switching, mitotic to meiotic cell cycle | IGI PMID:29084823 Phosphorylation of the RNA-binding protein Zfs1 modulates se... | ACCEPT | Summary: Genetic-interaction annotation with zfs1 (PomBase:SPBC1718.07c) from Navarro, Chakravarty & Nurse 2017 (full text cached). Zfs1 binds puc1+ mRNA and limits Puc1 accumulation; in zfs1 deletion cells Puc1 is elevated and mating efficiency drops about five-fold, and deleting puc1+ - but not cig1+ or cig2+ to the same extent - restores mating and the timely G1 arrest on nitrogen removal. Ectopic Puc1 inhibits mating in a dose-dependent manner. This confirms and extends Forsburg & Nurse 1994, where puc1 overexpression blocked sexual development and rescued pat1ts lethal meiosis. Reason: Puc1 is the cyclin that keeps nutrient-limited cells in the mitotic cycle and restrains entry into the sexual/meiotic programme; the effect is Puc1-specific among the G1 cyclins and is exerted through the Puc1-Cdc2 kinase (Rum1-resistant activity, proposed extended inhibitory phosphorylation of Ste11). This is a bona fide, well-supported core function of Puc1 rather than an indirect consequence of a cell-cycle defect, and the term matches PomBase usage for pombe differentiation regulators. Supporting Evidence: PMID:29084823 We found that Zfs1 negatively regulates the G1 cyclin Puc1, and deregulated Puc1 levels inhibit differentiation in the zfs1Δ mutant PMID:29084823 However, deletion of the puc1+ gene in the zfs1Δ mutant increased mating efficiency to WT values, suggesting that deregulation of puc1+ gene expression in the zfs1Δ mutant was a major contributor to the sexual differentiation defect PMID:29084823 Neither cig1+ nor cig2+ gene deletion suppressed the mating defect of the zfs1Δ mutant as efficiently as puc1+ gene deletion, indicating a specific role of Puc1 cyclin in the phenotype of the zfs1Δ mutant PMID:29084823 This experiment showed that Puc1 has a dose-dependent inhibitory effect over sexual differentiation, with increasing levels of Puc1 reducing mating efficiency to the levels observed in the zfs1Δ mutant PMID:29084823 The zfs1Δ mutant was able to arrest in G1 phase upon nitrogen depletion, but it did so with slower kinetics compared with the kinetics of the WT strain, a delay in cell cycle arrest that was suppressed by the deletion of the puc1+ gene PMID:29084823 This might be due to the ability of the Puc1–Cdc2 complex to phosphorylate and probably inactivate the CDK inhibitor Rum1 (Martin-Castellanos et al., 2000). Rum1, in contrast, cannot inactivate the Puc1–Cdc2 complex, and therefore, small changes in cyclin levels can result in dramatic changes in activity PMID:8006074 Overexpression of the puc1 protein blocks sexual development, and rescues pat1ts cells, which would otherwise undergo a lethal meiosis |
| GO:1900087 positive regulation of G1/S transition of mitotic cell cycle | EXP PMID:9201720 Ran1 functions to control the Cdc10/Sct1 complex through Puc... | ACCEPT | Summary: Experimental annotation from Caligiuri, Connolly & Beach 1997: Puc1 associates in vivo with the Ran1 (Pat1) protein kinase and with Cdc10, the DNA-binding subunit of the Sct1/Cdc10 (MBF) Start transcription complex; Ran1 controls the Puc1-Cdc10 association and Cdc10 phosphorylation changes when Ran1 is inactivated. Start execution requires Cdc2 and MBF, so the paper places the Puc1 cyclin physically at the Start transcription complex under Ran1 control. Reason: Direct biochemical evidence that the G1 cyclin engages the Start machinery, consistent with the positive G1/S role established genetically (complementation of cln deficiency; G1 delay of cig1 cig2 puc1 cells) and biochemically (Puc1-Cdc2 phosphorylation of Rum1). The cached record is abstract-only, but the abstract states the result explicitly; the curator's positive-regulation reading is accepted. Supporting Evidence: PMID:9201720 The execution of Start requires the activity of the Cdc2 protein kinase and the Sct1/Cdc10 transcription complex PMID:9201720 We demonstrate that the Puc1 cyclin associates with Ran1 and Cdc10 in vivo and that the Ran1 protein kinase functions to control the association between Puc1 and Cdc10 PMID:9201720 These results provide biochemical evidence that demonstrate one mechanism by which the Ran1 protein kinase serves to control cell fate through Cdc10 and Puc1 file:SCHPO/puc1/puc1-deep-research-falcon.md Accordingly, the favored mechanism is that Cdc2–Puc1 helps mark Rum1 for degradation near the end of G1. |
| GO:2000045 regulation of G1/S transition of mitotic cell cycle | IEA GO_REF:0000002 | MODIFY | Summary: InterPro2GO mapping of the CLN-type cyclin family signature (IPR014399 Cyclin_CLN) to regulation of the G1/S transition of the mitotic cell cycle. Reason: Correct family-level mapping - the Cln-type signature is exactly the family whose members regulate G1/S - but the direction of Puc1's effect is unambiguously positive (complementation of G1-arrested cln cells; Puc1-Cdc2 phosphorylation of Rum1), so the same signed child term proposed on the IGI row, positive regulation of G1/S transition of mitotic cell cycle (GO:1900087), is the consistent replacement. Proposed replacements: positive regulation of G1/S transition of mitotic cell cycle Supporting Evidence: PMID:1828291 We have isolated a G1-type cyclin gene called puc1+ from S. pombe, using a functional assay in S. cerevisiae PMID:1828291 At least one is required for progression through the G1-S phase, and deletion of all three leads to G1 arrest file:SCHPO/puc1/puc1-deep-research-falcon.md Accordingly, the favored mechanism is that Cdc2–Puc1 helps mark Rum1 for degradation near the end of G1. |
| GO:2000045 regulation of G1/S transition of mitotic cell cycle | IGI PMID:1828291 Identification of a G1-type cyclin puc1+ in the fission yeas... | MODIFY | Summary: Genetic-interaction annotation (with S. cerevisiae CLN3) from Forsburg & Nurse 1991: puc1+ was isolated because it rescues budding-yeast cells lacking G1-cyclin (CLN) function, which otherwise arrest in G1, and puc1+ expression in S. pombe indicates a G1-type cyclin role distinct from the mitotic B-type cyclin. Reason: The essence is right, but the direction of the effect is unambiguously positive: puc1+ relieves the G1 arrest of cln-deficient cells and, in S. pombe, Puc1-Cdc2 promotes G1 progression by phosphorylating Rum1. Positive regulation of G1/S transition of mitotic cell cycle (GO:1900087) - already carried by the EXP row - is the precise term; the unsigned parent adds nothing. Proposed replacements: positive regulation of G1/S transition of mitotic cell cycle Supporting Evidence: PMID:1828291 At least one is required for progression through the G1-S phase, and deletion of all three leads to G1 arrest PMID:1828291 We have isolated a G1-type cyclin gene called puc1+ from S. pombe, using a functional assay in S. cerevisiae file:SCHPO/puc1/puc1-deep-research-falcon.md Accordingly, the favored mechanism is that Cdc2–Puc1 helps mark Rum1 for degradation near the end of G1. |
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Download this section (compressed HTML)Q: Martin-Castellanos et al. 2000 (MBoC 11:543), the paper that established Puc1-Cdc2 phosphorylation of Rum1 T58/T62, the Rum1-resistance of the Puc1-Cdc2 kinase and the G1/size phenotype of cig1 cig2 puc1 cells, is not among the GOA references for puc1; should it be curated (IGI with cig1/cig2 for G1/S transition, and a Cdc2 has-input Rum1 relationship in a GO-CAM of the fission-yeast Start module)?
Q: What is the physiological substrate through which Puc1-Cdc2 restrains sexual differentiation - Rum1 destabilisation, extended inhibitory phosphorylation of Ste11, or the Cdc10/MBF complex it associates with under Ran1 control - and is 'negative regulation of cell cycle switching, mitotic to meiotic cell cycle' the intended level, given that the measured phenotype is mating (conjugation) efficiency and G1 arrest kinetics?
Q: Where is endogenous Puc1 through the cell cycle and during nitrogen starvation? The only localization data are a proteome-wide YFP screen (nucleus and cytosol); is the cytosolic pool a site of action or a sequestered/synthesis pool as for budding-yeast Cln3?
Experiment: Combine an analog-sensitive cdc2-as allele with a rapidly degradable (AID) Puc1 in zfs1 deletion cells, and follow Ste11 and Rum1 phosphorylation and Ste11-dependent transcription (ste11+, mei2+) by phospho-proteomics and RNA-seq within minutes of Puc1 depletion during nitrogen withdrawal; test phospho-site mutants of Ste11 and Rum1 (T58A/T62A) for suppression of the Puc1-overexpression mating block.
Hypothesis: Puc1-Cdc2 restrains sexual differentiation by direct phosphorylation of Ste11 and/or Rum1 rather than through bulk CDK activity.
Experiment: Image endogenously tagged Puc1 (an mNeonGreen knock-in at the puc1 locus preserving the UTRs, as in the puc1-V5 allele) in single cells across the cycle and during nitrogen starvation, quantify nuclear/cytosolic ratios, and test NLS/NES-tagged Puc1 variants for rescue of the cig1 cig2 puc1 G1 delay and of the zfs1 mating defect.
Hypothesis: Puc1 accumulates in the nucleus in late G1 and at the cycling/non-cycling transition, and nuclear localization is required for its function.
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