The research report should be a detailed narrative explaining the function, biological processes, and localization of the gene product. Citations should be given for all claims.
You should prioritize authoritative reviews and primary scientific literature when conducting research. You can supplement
this with annotations you find in gene/protein databases, but these can be outdated or inaccurate.
We are specifically interested in the primary function of the gene - for enzymes, what reaction is catalyzed, and what is the substrate specificity? For transporters, what is the substrate? For structural proteins or adapters, what is the broader structural role? For signaling molecules, what is the role in the pathway.
We are interested in where in or outside the cell the gene product carries out its function.
We are also interested in the signaling or biochemical pathways in which the gene functions. We are less interested in broad pleiotropic effects, except where these elucidate the precise role.
Include evidence where possible. We are interested in both experimental evidence as well as inference from structure, evolution, or bioinformatic analysis. Precise studies should be prioritized over high-throughput, where available.
The requested identity is verified: puc1 (SPBC19F5.01c; UniProt P25009) encodes the fission-yeast cyclin Puc1, a Cln-related/G1-type cyclin in Schizosaccharomyces pombe. This agrees with the supplied cyclin, cyclin-like, Cyclin_CLN, and Cyclin_N domain assignments. The literature reviewed here concerns the correct organism and protein; findings about similarly named genes were not used.
Puc1 is not itself an enzyme. Its primary molecular function is to act as a regulatory cyclin for the principal cell-cycle CDK, Cdc2. The best-supported biochemical mechanism is that the Cdc2–Puc1 kinase complex promotes late-G1 progression by phosphorylating the CDK inhibitor Rum1 at Thr58 and Thr62, facilitating Rum1 down-regulation and thereby releasing B-type Cdc2–cyclin activities needed for S phase. Puc1 is partly redundant with Cig1 and Cig2: deleting puc1 alone causes little phenotype, whereas deleting all three cyclins markedly prolongs G1, increases the size threshold for S phase, and accelerates starvation-induced G1 arrest and mating. Puc1 can facilitate G1 progression but cannot independently execute DNA replication in the absence of the relevant B-type cyclins. Its precise subcellular localization and a broad physiological substrate spectrum remain unresolved.
| Topic | Best-supported conclusion | Evidence type | Key quantitative observation | Source/year |
|---|---|---|---|---|
| Identity | Puc1/P25009 is the S. pombe G1 cyclin described as Cln-like; this matches the supplied UniProt cyclin-family/domain annotation. | Sequence relationship plus functional complementation and genetics | Expression rescued a Saccharomyces cerevisiae cln1Δ cln2Δ cln3Δ background. | Forsburg & Nurse, 1991; Martín-Castellanos et al., 2000 (martıncastellanos2000thepuc1cyclin pages 2-3, martıncastellanos2000thepuc1cyclin pages 1-2) |
| Cdc2 association | Puc1 associates with the principal cell-cycle CDK Cdc2 and functions as its regulatory cyclin rather than as an enzyme itself. | Biochemical association; kinase immunocomplex assays | No binding constant or complex stoichiometry was reported in the available evidence. | Martín-Castellanos et al., 2000 (martıncastellanos2000thepuc1cyclin pages 1-2) |
| Rum1 phosphorylation and resistance | Cdc2–Puc1 can phosphorylate the CDK inhibitor Rum1 at T58 and T62 in vitro, sites linked to SCF-dependent Rum1 degradation; unlike Cdc2–Cdc13 and Cdc2–Cig2, its kinase activity is comparatively resistant to Rum1 inhibition. | Site-mutant substrate and immunoprecipitated-kinase assays | Wild-type Rum1 shifted from 34 to 36 kDa after phosphorylation; the T58A/T62A substrate did not shift. At 10 nM Rum1, Cdc13 activity was inhibited and Cig2 activity was nearly abolished, whereas Puc1-associated activity was not significantly inhibited. | Martín-Castellanos et al., 2000 (martıncastellanos2000thepuc1cyclin pages 5-7, martıncastellanos2000thepuc1cyclin pages 9-10) |
| Redundancy with Cig1/Cig2 | Puc1 has a partly redundant G1-promoting role with Cig1 and Cig2. A puc1Δ single mutant has little overt phenotype, but loss of all three cyclins strongly prolongs G1; the triple mutant remains viable because other cyclin–CDK activity can support the cycle. | Single-, double-, and triple-deletion genetics; flow cytometry | G1 fractions were about 6% in cig2Δ puc1Δ and 17% in cig1Δ cig2Δ puc1Δ cells; in a wee1-50 background these rose to approximately 20% and 40%, respectively. | Martín-Castellanos et al., 2000 (martıncastellanos2000thepuc1cyclin pages 2-3, martıncastellanos2000thepuc1cyclin pages 3-4) |
| G1 and cell-size control | Puc1 helps couple G1 progression to attainment of critical cell size, especially when Cig1/Cig2 are absent or nutrients are limiting. The phenotype depends strongly on Rum1. | Deletion genetics, cell-size measurements, flow cytometry, and epistasis | Triple-mutant cells were approximately 15% larger than wild type during vegetative growth and entered S phase after growing to about 2.5-fold wild-type size following nitrogen refeeding; deleting rum1 abolished the excess G1 population. | Martín-Castellanos et al., 2000 (martıncastellanos2000thepuc1cyclin pages 4-5, martıncastellanos2000thepuc1cyclin pages 5-7, martıncastellanos2000thepuc1cyclin pages 9-10) |
| Nitrogen starvation and hyperfertility | Cig1/Cig2/Puc1 collectively delay premature G1 arrest and mating as nutrients decline; the triple mutant exits the mitotic cycle earlier and is hyperfertile. This establishes a pathway-level role but does not assign the phenotype uniquely to Puc1. | Nitrogen-starvation time course, flow cytometry, microscopy, and mating phenotype | After nitrogen withdrawal, more than 90% of triple-mutant cells were in G1 by 3 h and 100% by 4 h after one division; approximately 25% had begun conjugation by 4 h, before wild-type cells. | Martín-Castellanos et al., 2000 (martıncastellanos2000thepuc1cyclin pages 7-9, martıncastellanos2000thepuc1cyclin pages 3-4) |
| Capacity to drive S phase | Puc1 promotes progression through G1 but, unlike B-type cyclins, cannot independently trigger DNA replication. Its best-supported primary role is relief of G1 inhibition, not direct execution of S phase. | Cyclin-deletion and complementation genetics; mechanistic interpretation | Puc1 did not induce S-phase entry in cells lacking cig1, cig2, and cdc13. | Fisher & Nurse, 1996; Martín-Castellanos et al., 2000 (martıncastellanos2000thepuc1cyclin pages 10-11, martıncastellanos2000thepuc1cyclin pages 9-10) |
| Meiosis | A direct, nonredundant meiotic function for Puc1 is not established. Triple-mutant cells can mate, undergo meiosis and sporulation, and produce colony-forming spores; Puc1 was excluded from a later meiotic-recombination analysis because its meiotic-prophase expression was nearly undetectable. | Genetic viability/fertility observations and expression-based study design | No Puc1-specific recombination statistic was reported; expression during meiotic prophase was described as almost undetectable and below vegetative levels. | Martín-Castellanos et al., 2000; Bustamante-Jaramillo et al., 2019 (bustamantejaramillo2019cdkcontributionto pages 3-5, martıncastellanos2000thepuc1cyclin pages 9-10) |
| Localization | The available Puc1-specific literature does not establish a definitive subcellular localization. Nuclear action is mechanistically plausible because Cdc2–Puc1 acts on cell-cycle regulators, but it should not be asserted as experimentally demonstrated for Puc1 from these sources. | Evidence gap; inference explicitly withheld | The 2022 spatial survey quantified thousands of cells for numerous regulators but the available passage does not report a Puc1 localization measurement. | Curran et al., 2022 (curran2022aquantitativeand pages 7-8) |
Table: Evidence supporting the functional annotation of Schizosaccharomyces pombe Puc1/P25009, with direct findings separated from pathway-level inference and unresolved localization or meiotic roles.
The foundational literature identifies puc1 as an S. pombe G1-type cyclin closely related to the Cln cyclins of budding yeast. Functional complementation supports this classification: Puc1 expression could rescue a budding-yeast background lacking CLN1, CLN2, and CLN3. Subsequent work placed Puc1 among the cyclins that associate with S. pombe Cdc2. These observations are fully consistent with the UniProt accession, description, organism, and cyclin-family/domain information supplied in the query. (martıncastellanos2000thepuc1cyclin pages 2-3, martıncastellanos2000thepuc1cyclin pages 1-2)
The symbol is potentially searchable in unrelated contexts, but the relevant literature consistently uses Puc1/puc1+ for the fission-yeast cyclin. No functional claim in this report is transferred from a different organism or similarly named protein.
Puc1 is a noncatalytic regulatory subunit that associates with Cdc2, the major S. pombe cell-cycle CDK. Cyclin binding activates and helps determine the timing and substrate engagement of CDK activity. Thus, the relevant catalytic activity belongs to Cdc2–Puc1, not isolated Puc1. (martıncastellanos2000thepuc1cyclin pages 1-2)
The strongest direct substrate evidence concerns Rum1, a G1 CDK inhibitor. Puc1 and Cdc2 immunocomplexes phosphorylated Rum1 in vitro at Thr58 and Thr62. Phosphorylated wild-type Rum1 shifted electrophoretically from approximately 34 to 36 kDa, whereas a T58A/T62A Rum1 mutant did not shift. These residues are associated with recognition by the SCF^Pop1/Pop2 ubiquitin-proteolysis pathway. Accordingly, the favored mechanism is that Cdc2–Puc1 helps mark Rum1 for degradation near the end of G1. (martıncastellanos2000thepuc1cyclin pages 5-7, martıncastellanos2000thepuc1cyclin pages 9-10)
Cdc2–Puc1 is well suited to initiate this transition because its measured histone-H1 kinase activity was comparatively resistant to Rum1. 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. This suggests a feedback-breaking role: Cdc2–Puc1 can remain active in the presence of Rum1, phosphorylate Rum1, and thereby permit activation of Rum1-sensitive B-type cyclin complexes. (martıncastellanos2000thepuc1cyclin pages 5-7)
Rum1 Thr58/Thr62 is the best-supported Puc1-complex substrate in the retrieved evidence. Histone H1 was used as a generic kinase-assay substrate, not established as a physiological Puc1 target. Ste9/APC has been proposed as another downstream target or pathway component, but the available Puc1-specific evidence does not establish direct Ste9 phosphorylation. Therefore, it would be premature to assign Cdc2–Puc1 a broad or unique physiological substrate motif from these studies. (martıncastellanos2000thepuc1cyclin pages 1-2, martıncastellanos2000thepuc1cyclin pages 5-7, martıncastellanos2000thepuc1cyclin pages 9-10)
The principal biological role of Puc1 is to promote progression through G1 and help couple Start/S-phase entry to cell size. Early in G1, Rum1 and Ste9/APC maintain low Cdc2–cyclin activity. As cells reach the appropriate size, Cdc2–Puc1 and related complexes help reverse that inhibitory state, enabling B-type cyclin–Cdc2 activity and subsequent S-phase entry. (martıncastellanos2000thepuc1cyclin pages 1-2, martıncastellanos2000thepuc1cyclin pages 9-10)
Puc1's contribution is masked by redundancy. A puc1Δ single mutant, and even puc1Δ cig1Δ, showed little overt vegetative phenotype. However, deleting puc1 in a cig1Δ cig2Δ background produced a marked G1 delay and increased the cell size at which DNA replication began. The triple mutant was approximately 15% larger than wild type during vegetative growth. The observed G1 fractions were approximately 6% in cig2Δ puc1Δ and 17% in cig1Δ cig2Δ puc1Δ cells; in a sensitized wee1-50 background these values increased to about 20% and 40%, respectively. (martıncastellanos2000thepuc1cyclin pages 2-3, martıncastellanos2000thepuc1cyclin pages 3-4, martıncastellanos2000thepuc1cyclin pages 9-10)
The genetic relationship to Rum1 is strong. Deleting rum1 from the triple-cyclin mutant completely abolished the excess G1 population and yielded a phenotype resembling rum1Δ. This epistasis supports the interpretation that excess or prolonged Rum1 activity is a major cause of the G1 delay when Puc1, Cig1, and Cig2 are absent. Nevertheless, Rum1 was eventually degraded and cells remained viable, showing that Cdc13-associated or other activity can compensate. (martıncastellanos2000thepuc1cyclin pages 5-7, martıncastellanos2000thepuc1cyclin pages 9-10)
Puc1 should be annotated as a G1-promoting cyclin, not as the cyclin that directly performs all S-phase functions. Puc1 did not cause S-phase entry in cells lacking cig1, cig2, and cdc13. The literature consequently distinguishes relief of G1 inhibition by Puc1 from the replication-promoting activity of B-type Cdc2–cyclin complexes. (martıncastellanos2000thepuc1cyclin pages 10-11, martıncastellanos2000thepuc1cyclin pages 9-10)
Puc1 acts within a broader nutrient-responsive G1 control system. Under nitrogen starvation, wild-type cells normally complete approximately two divisions before accumulating in G1. The cig1Δ cig2Δ puc1Δ mutant arrested after only one division: more than 90% of cells were in G1 by 3 hours and 100% by 4 hours. Approximately 25% of homothallic triple-mutant cells had initiated conjugation at 4 hours, when wild-type cells had not yet begun conjugating. This establishes that the three cyclins collectively restrain premature cell-cycle exit and sexual differentiation as nutrients decline. (martıncastellanos2000thepuc1cyclin pages 3-4)
After nitrogen starvation, triple-mutant cells arrested at approximately twice wild-type size and had to grow to approximately 2.5 times wild-type size before entering S phase following nitrogen readdition. Rum1 disappearance was delayed from 2–3 hours after refeeding in wild type to 3–5 hours in the triple mutant. These quantitative results connect cyclin-dependent Rum1 down-regulation to nutrient-sensitive size control. (martıncastellanos2000thepuc1cyclin pages 4-5)
The phenotypes cannot be assigned exclusively to Puc1 because they were measured in the triple mutant. The justified interpretation is that Puc1 makes a redundant but physiologically relevant contribution, particularly when other G1 cyclins are absent or growth is nutrient limited.
A unique meiotic function for Puc1 is not established. Cells lacking Puc1, Cig1, and Cig2 could mate, complete meiosis and sporulation, and produce spores capable of colony formation. Later work on meiotic recombination did not include Puc1 in its focused cyclin analysis because puc1 expression was almost undetectable during meiotic prophase and lower than in vegetative cells. That study instead identified contributions from Cig1, Cig2, and Crs1. (bustamantejaramillo2019cdkcontributionto pages 3-5, martıncastellanos2000thepuc1cyclin pages 9-10)
Accordingly, Puc1 may contribute redundantly to early meiotic G1 progression, but evidence does not support annotating it as a principal meiotic-recombination cyclin. Reviews emphasizing that a single Cdc13–Cdc2 module can support broad mitotic and meiotic progression reinforce the extensive functional redundancy of the fission-yeast cyclin network. (mackenzie2020cdkregulationof pages 21-23)
The retrieved Puc1-specific studies do not establish a definitive localization by direct microscopy or fractionation. A nuclear site of action is plausible because Cdc2–Puc1 regulates nuclear cell-cycle transitions and Rum1, but plausibility is not equivalent to demonstrated Puc1 localization.
A 2022 systems-level spatial study found that many S. pombe cell-cycle regulators were nuclear-enriched and that several core CDK regulators also associated with the spindle-pole body. However, the available Puc1-specific evidence did not report a Puc1 localization measurement, so those general observations should not be transferred to Puc1 without direct data. (curran2022aquantitativeand pages 7-8)
Recommended annotation: “Intracellular cell-cycle regulator; precise Puc1 subcellular localization not firmly established in the cited primary literature.”
Puc1 is nonessential under standard laboratory conditions. Even combined deletion of puc1, cig1, and cig2 was viable, although cells were enlarged, delayed in G1, hyperfertile, and more responsive to nitrogen starvation. Cdc13 is sufficient to support essential cell-cycle progression in this genetic context. (martıncastellanos2000thepuc1cyclin pages 2-3, martıncastellanos2000thepuc1cyclin pages 9-10)
This redundancy explains why a single-gene deletion understates Puc1's function. The strongest annotation comes from combinatorial genetics and biochemical assays rather than from the mild puc1Δ phenotype alone. It also cautions against describing Puc1 as either dispensable in every physiological setting or as the sole G1-size sensor.
The recent literature located by this search largely preserves, rather than overturns, the foundational model. A 2024 review of sexual-differentiation initiation classifies Puc1 as the S. pombe G1-type cyclin alongside Cdc13 and the G1/S cyclins. Recent general CDK reviews likewise emphasize that cyclin–CDK systems coordinate cell-cycle progression with transcriptional and physiological state. (kawamukai2024regulationofsexual pages 3-4)
No 2023–2024 primary study retrieved here supplied a new Puc1-specific structure, interactome, localization, physiological substrate, or mechanism. Consequently, the mechanistic annotation still rests chiefly on the 1991 discovery and the detailed 2000 genetic/biochemical analysis. This is an important negative result of the literature review: “latest research” for Puc1 consists mainly of modern pathway context, not a newly defined Puc1 mechanism.
Puc1 has no established clinical, diagnostic, agricultural, or industrial application in the literature reviewed. Its current value is primarily as a basic-research component of the fission-yeast cell-cycle model, with applications in:
The most defensible expert interpretation is that Puc1 is a specialized but redundant G1 gate-opening cyclin. Its importance becomes evident in sensitized genetic or nutritional conditions, while the essential replication and mitotic functions can be carried by B-type cyclin–Cdc2 complexes.
High confidence: correct identity as the S. pombe Cln-like/G1 cyclin; Cdc2 association; nonessentiality; redundant promotion of G1 progression; Rum1 T58/T62 phosphorylation in vitro; resistance of Puc1-associated kinase to Rum1 inhibition; increased G1 duration and size threshold when Puc1, Cig1, and Cig2 are absent. (martıncastellanos2000thepuc1cyclin pages 1-2, martıncastellanos2000thepuc1cyclin pages 5-7, martıncastellanos2000thepuc1cyclin pages 9-10)
Moderate confidence: Cdc2–Puc1 promotes Rum1 destruction in vivo and thereby releases B-type CDK activity. This model is strongly supported by biochemistry and genetic epistasis, but redundancy prevents attribution of all in-vivo Rum1 turnover specifically to Puc1. (martıncastellanos2000thepuc1cyclin pages 5-7, martıncastellanos2000thepuc1cyclin pages 9-10)
Unresolved: direct Puc1 localization; three-dimensional structure; complete physiological substrate spectrum; whether Ste9/APC is a direct Cdc2–Puc1 substrate; Puc1-specific quantitative abundance through the cell cycle; and a unique meiotic role.
References
(martıncastellanos2000thepuc1cyclin pages 2-3): Cristina Martı́n-Castellanos, Miguel A. Blanco, José M. de Prada, and Sergio Moreno. The puc1 cyclin regulates the g1 phase of the fission yeast cell cycle in response to cell size. Molecular biology of the cell, 11 2:543-54, Feb 2000. URL: https://doi.org/10.1091/mbc.11.2.543, doi:10.1091/mbc.11.2.543. This article has 111 citations and is from a domain leading peer-reviewed journal.
(martıncastellanos2000thepuc1cyclin pages 1-2): Cristina Martı́n-Castellanos, Miguel A. Blanco, José M. de Prada, and Sergio Moreno. The puc1 cyclin regulates the g1 phase of the fission yeast cell cycle in response to cell size. Molecular biology of the cell, 11 2:543-54, Feb 2000. URL: https://doi.org/10.1091/mbc.11.2.543, doi:10.1091/mbc.11.2.543. This article has 111 citations and is from a domain leading peer-reviewed journal.
(martıncastellanos2000thepuc1cyclin pages 5-7): Cristina Martı́n-Castellanos, Miguel A. Blanco, José M. de Prada, and Sergio Moreno. The puc1 cyclin regulates the g1 phase of the fission yeast cell cycle in response to cell size. Molecular biology of the cell, 11 2:543-54, Feb 2000. URL: https://doi.org/10.1091/mbc.11.2.543, doi:10.1091/mbc.11.2.543. This article has 111 citations and is from a domain leading peer-reviewed journal.
(martıncastellanos2000thepuc1cyclin pages 9-10): Cristina Martı́n-Castellanos, Miguel A. Blanco, José M. de Prada, and Sergio Moreno. The puc1 cyclin regulates the g1 phase of the fission yeast cell cycle in response to cell size. Molecular biology of the cell, 11 2:543-54, Feb 2000. URL: https://doi.org/10.1091/mbc.11.2.543, doi:10.1091/mbc.11.2.543. This article has 111 citations and is from a domain leading peer-reviewed journal.
(martıncastellanos2000thepuc1cyclin pages 3-4): Cristina Martı́n-Castellanos, Miguel A. Blanco, José M. de Prada, and Sergio Moreno. The puc1 cyclin regulates the g1 phase of the fission yeast cell cycle in response to cell size. Molecular biology of the cell, 11 2:543-54, Feb 2000. URL: https://doi.org/10.1091/mbc.11.2.543, doi:10.1091/mbc.11.2.543. This article has 111 citations and is from a domain leading peer-reviewed journal.
(martıncastellanos2000thepuc1cyclin pages 4-5): Cristina Martı́n-Castellanos, Miguel A. Blanco, José M. de Prada, and Sergio Moreno. The puc1 cyclin regulates the g1 phase of the fission yeast cell cycle in response to cell size. Molecular biology of the cell, 11 2:543-54, Feb 2000. URL: https://doi.org/10.1091/mbc.11.2.543, doi:10.1091/mbc.11.2.543. This article has 111 citations and is from a domain leading peer-reviewed journal.
(martıncastellanos2000thepuc1cyclin pages 7-9): Cristina Martı́n-Castellanos, Miguel A. Blanco, José M. de Prada, and Sergio Moreno. The puc1 cyclin regulates the g1 phase of the fission yeast cell cycle in response to cell size. Molecular biology of the cell, 11 2:543-54, Feb 2000. URL: https://doi.org/10.1091/mbc.11.2.543, doi:10.1091/mbc.11.2.543. This article has 111 citations and is from a domain leading peer-reviewed journal.
(martıncastellanos2000thepuc1cyclin pages 10-11): Cristina Martı́n-Castellanos, Miguel A. Blanco, José M. de Prada, and Sergio Moreno. The puc1 cyclin regulates the g1 phase of the fission yeast cell cycle in response to cell size. Molecular biology of the cell, 11 2:543-54, Feb 2000. URL: https://doi.org/10.1091/mbc.11.2.543, doi:10.1091/mbc.11.2.543. This article has 111 citations and is from a domain leading peer-reviewed journal.
(bustamantejaramillo2019cdkcontributionto pages 3-5): Luisa F. Bustamante-Jaramillo, Celia Ramos, Leticia Alonso, Aroa Sesmero, Mónica Segurado, and Cristina Martín-Castellanos. Cdk contribution to dsb formation and recombination in fission yeast meiosis. PLOS Genetics, 15:e1007876, Jan 2019. URL: https://doi.org/10.1371/journal.pgen.1007876, doi:10.1371/journal.pgen.1007876. This article has 16 citations and is from a domain leading peer-reviewed journal.
(curran2022aquantitativeand pages 7-8): Scott Curran, Gautam Dey, Paul Rees, and Paul Nurse. A quantitative and spatial analysis of cell cycle regulators during the fission yeast cycle. Proceedings of the National Academy of Sciences, Aug 2022. URL: https://doi.org/10.1073/pnas.2206172119, doi:10.1073/pnas.2206172119. This article has 29 citations and is from a highest quality peer-reviewed journal.
(mackenzie2020cdkregulationof pages 21-23): Anne M. MacKenzie and Soni Lacefield. Cdk regulation of meiosis: lessons from s. cerevisiae and s. pombe. Genes, 11:723, Jun 2020. URL: https://doi.org/10.3390/genes11070723, doi:10.3390/genes11070723. This article has 46 citations.
(kawamukai2024regulationofsexual pages 3-4): Makoto Kawamukai. Regulation of sexual differentiation initiation in schizosaccharomyces pombe. Bioscience, biotechnology, and biochemistry, 88:475-492, Mar 2024. URL: https://doi.org/10.1093/bbb/zbae019, doi:10.1093/bbb/zbae019. This article has 17 citations.