Biology subjects

Nurse, P.

Publications and source records attributed to Nurse, P..

8 recordsLinked to original sources

bioRxiv2026

AlphaFold-Multimer reveals diverse cyclin-CDK substrate docking interactions

Cyclin-dependent kinases (CDKs) control eukaryotic cell-cycle progression by phosphorylating specific substrates with substrate recognition often involving cyclin-specific docking interactions. However, in minimal cell cycle control systems driven by a single cyclin-CDK complex, how docking interactions contribute to the differential timing of substrate phosphorylation remains unclear. Here, we used AlphaFold-Multimer to systematically predict interactions between the fission yeast mitotic cyclin-CDK fusion Cdc13-L-Cdc2 and its known in vivo CDK substrates. We found that many substrates are predicted to interact with the cyclin hydrophobic patch, and have identified a previously uncharacterised docking motif, [FVIPWGLAM](x)xER[LMV] (ERL motif), with features consistent with an atypical RxL motif. We show that ERL motifs can functionally substitute for canonical RxL motifs to promote phosphorylation of a model CDK substrate by Cdc13-Cdc2, while the S-phase cyclin-CDK Cig2-Cdc2 was found to preferentially phosphorylate substrates containing canonical RxL motifs. Finally, we investigated whether Cdc13-L-Cdc2 is predicted to preferentially bind DNA replication substrates over mitotic substrates but found no evidence of differential binding. These results reveal diversity in cyclin-CDK substrate recognition beyond established docking motifs.

Cell Biology↗

bioRxiv2025

Control of CDK activity and the cell cycle by CKS proteins

The eukaryotic cell cycle is orchestrated by the activity of Cyclin-Dependent Kinases (CDKs)1. Although most mechanisms controlling CDK activity are well understood, one class of proteins - the CDK regulatory subunit (CKS) proteins - remain highly enigmatic. There is no generally accepted consistent molecular or functional characterisation of CKS in vivo, despite being essential across eukaryotes and implicated in a range of cell cycle processes and cancer2,3. Here, we provide a unifying framework for CKS function. We show in a single, genetically tractable system, the fission yeast, that CKS regulates the onset and progression of both S-phase and mitosis. We find that CKS modulates the phosphorylation of more than 200 CDK phosphosites in vivo, located on 133 substrate proteins. These are involved in diverse processes across the entire cell cycle, including DNA replication, chromosome condensation, the spindle assembly checkpoint, and the metaphase-anaphase transition. We demonstrate that CKS enhances CDK activity to drive phosphorylation of sites with low affinity for CDK. This acts both on specific substrates, likely by stabilizing CDK-substrate interactions, and through control of overall CDK activity, by regulating its interaction with Wee1 and Cdc25. Our findings establish CKS proteins as major multifaceted regulators of the cell cycle, operating through the global and local control of CDK activity.

cell biology↗

bioRxiv2025

Phosphatase specificity influences phosphorylation timing of CDK substrates during the cell cycle

Cell cycle events are ordered by cyclin-dependent kinases (CDKs), which phosphorylate hundreds of substrates. Multiple phosphatases oppose CDK substrate phosphorylation, yet a systematic understanding of how these phosphatases collectively influence phosphorylation timing is lacking. Here, we show that phosphatases influence the timing of CDK substrate phosphorylation during G2 and mitosis in fission yeast. We identify substrates of four phosphatases (PP2A-B55, PP2A-B56, CDC14, and PP1), showing that each phosphatase targets a distinct subset of CDK substrate sites. On average, sites dephosphorylated by CDC14 and PP2A-B56 are phosphorylated earlier during G2, followed by sites dephosphorylated by PP1 and then PP2A-B55. This suggests that the identity of the phosphatase impacts the timing of CDK substrate phosphorylation, establishing different phosphorylation thresholds at the G2/M transition. Consistent with this, depletion of PP2A-B55 and CDC14 advances mitotic onset independently of CDK activity regulation, likely due to the earlier phosphorylation of their respective CDK substrates.

cell biology↗

bioRxiv2024

Spatiotemporal Orchestration of Mitosis by Cyclin-Dependent Kinase

Mitotic onset is a critical transition for eukaryotic cell proliferation. The prevailing view for its control is that cyclin-dependent kinase (CDK) is activated first in the cytoplasm, at the centrosome, which then initiates mitosis1-3. Bistability in CDK activation ensures the transition is irreversible but how this unfolds in a spatially compartmentalized cell is unknown4-8. Here using fission yeast, we show that CDK is actually activated in the nucleus first, not the cytoplasm, and that the bistable responses dramatically differ within the nucleus and cytoplasm. There is a stronger response in the nucleus permitting mitotic signal propagation from there to the cytoplasm. Abolishing cyclin-CDK localization to the yeast centrosome led to activation occurring only in the nucleus, spatially uncoupling the nucleus and cytoplasm mitotically, suggesting centrosomal cyclin-CDK acts as a "signal relayer". We propose that the key mitotic regulatory system operates in the nucleus in proximity to DNA, allowing incomplete DNA replication and DNA damage to be effectively monitored to preserve genome integrity and for integration of ploidy within the CDK control network. This spatiotemporal regulatory framework establishes core principles for control of the onset of mitosis in vivo, which will help inform how CDK controls mitotic onset in other eukaryotes.

cell biology↗

bioRxiv2023

CDK activity at the centrosome regulates the cell cycle

Cyclin-dependent kinases (CDKs) complexed with cyclins drive progression through the eukaryotic cell cycle. From yeast to human cells, cyclin-CDK localises to the centrosome, but the importance of this localisation is unclear. The conserved hydrophobic patch substrate docking site on human Cyclin B1 and on the equivalent fission yeast Cdc13 mediates their localisation to the centrosome and the spindle-pole body (SPB, yeast centrosome equivalent). A hydrophobic patch mutant (HPM) of Cdc13 cannot enter mitosis, but whether this mitotic defect is due to defective SPB localisation or defective cyclin-substrate docking is unknown. Here we show that artificially restoring Cdc13HPM SPB localisation in fission yeast partially rescues both mitosis and defective CDK substrate phosphorylation at both the SPB and within the cytoplasm. In addition, we found that an HPM of the S-phase cyclin Cig2 has defective SPB localisation but is still able to perform bulk DNA synthesis. Our results demonstrate that the hydrophobic patch mediates the SPB localisation of both S- and M-phase cyclins, and that Cdc13 SPB localisation is essential for mitotic entry and for full phosphorylation of CDK substrates, supporting the view that the centrosome plays a role as a signalling hub regulating CDK cell cycle control.

cell biology↗

bioRxiv2022

Rates of global cellular translation and transcription during cell growth and the cell cycle in fission yeast.

Proliferating eukaryotic cells grow and undergo cycles of cell division. Growth is continuous whilst the cell cycle consists of discrete events. How the production of biomass is controlled as cells increase in size and proceed through the cell cycle is important for understanding the regulation of global cellular growth. This has been studied for decades but has not yielded consistent results. Previous studies investigating how cell size, the amount of DNA, and cell cycle events affect the global cellular production of proteins and RNA molecules have led to highly conflicting results, probably due to perturbations induced by the synchronisation methods used. To avoid these perturbations, we have developed a system to assay unperturbed exponentially growing populations of fission yeast cells. We generated thousands of single-cell measurements of cell size, of cell cycle stage, and of the levels of global cellular translation and transcription. This has allowed us to determine how cellular changes arising from progression through the cell cycle and cells growing in size affect global cellular translation and transcription. We show that translation scales with size, and additionally increases at late S-phase/early G2, then increases early in mitosis and decreases later in mitosis, suggesting that cell cycle controls are operative over global cellular translation. Transcription increases with both size and the amount of DNA, suggesting that the level of transcription of a cell may be the result of a dynamic equilibrium between the number of RNA polymerases associating and disassociating from DNA.

cell biology↗

bioRxiv2022

A quantitative and spatial analysis of cell cycle regulators during the fission yeast cell cycle

We have carried out a systems-level analysis of the spatial and temporal dynamics of cell cycle regulators in the fission yeast Schizosaccharomyces pombe. In a comprehensive single cell analysis we have precisely quantified the levels of 38 proteins previously identified as regulators of the G2 to mitosis transition, and of 7 proteins acting at the G1 to S-phase transition. Only two of the 38 mitotic regulators exhibit changes in concentration at the whole cell level, the mitotic B-type cyclin Cdc13 which accumulates continually throughout the cell cycle, and the regulatory phosphatase Cdc25 which exhibits a complex cell cycle pattern. Both proteins show similar patterns of change within the nucleus as in the whole cell but at higher concentrations. In addition, the concentrations of the major fission yeast cyclin dependent kinase (CDK) Cdc2, the CDK regulator Suc1 and the inhibitory kinase Wee1 also increase in the nucleus peaking at mitotic onset but are constant in the whole cell. The significant increase in concentration with size for Cdc13 supports the model that mitotic B-type cyclin accumulation acts as a cell size sensor. We propose a two-step process for the control of mitosis. First, Cdc13 accumulates in a size-dependent manner which drives increasing CDK activity. Second, from mid G2 the increasing nuclear accumulation of Cdc25 and the counteracting Wee1 introduces a bistability switch that results in a rapid rise of CDK activity at the end of G2 and thus brings about an orderly progression into mitosis. Significance StatementAcross eukaryotes the increasing level of cyclin dependent kinase (CDK) activity drives progression through the cell cycle. As most cells divide at specific sizes, information responding to the size of the cell must feed into the regulation of CDK activity. In this study, we use fission yeast to precisely measure how proteins that have been previously identified in genome wide screens as cell cycle regulators change in their levels with cell cycle progression. We identify the mitotic B-type cyclin Cdc13 and mitotic inhibitory phosphatase Cdc25 as the only two proteins that change in both whole cell and nuclear concentration through the cell cycle, making them candidates for universal cell size sensors at the onset of mitosis and cell division.

cell biology↗

bioRxiv2020

Synergistic CDK control pathways maintain cell size homeostasis

To coordinate cell size with cell division, cell size must be computed by the cyclin-CDK control network to trigger division appropriately. Here we dissect determinants of cyclin-CDK activity using a novel high-throughput single-cell in vivo system. We show that inhibitory phosphorylation of CDK encodes cell size information and works synergistically with PP2A to prevent division in smaller cells. However, even in the absence of all canonical regulators of cyclin-CDK, small cells with high cyclin-CDK levels are restricted from dividing. We find that diploid cells of equivalent size to haploid cells exhibit lower CDK activity in response to equal cyclin-CDK enzyme concentrations, suggesting that CDK activity is reduced by DNA concentration. Thus, multiple pathways directly regulate cyclin-CDK activity to maintain robust cell size homeostasis.

cell biology↗