A nuclear tale of two yeasts

2001 ◽  
Vol 114 (10) ◽  
pp. 1798-1799
Author(s):  
S.K. Evans ◽  
V. Lundblad

The Yeast Nucleus edited by P. Fantes and J. Beggs Oxford University Press (2000) 338 pages. ISBN 0–19-963772-5?32.50 Without question, numerous studies in yeast and mammals have revealed a striking commonality of underlying mechanisms that govern basic biological operations. Perhaps the most famous example from recent years has been the recognition that genes required for maintaining the yeast genome play a critical role in preventing cancer in humans. However, examining the molecular differences - the variations on a common theme, so to speak - can also be useful for understanding core biological processes. These ideas are the foundation for The Yeast Nucleus, a valuable contribution to Oxford University Press's ‘Frontiers in Molecular Biology’ series. The textbook compares and contrasts various nuclear processes in budding yeast (Saccharomyces cerevisiae) and fission yeast (Schizosaccharomyces pombe), pointing out the similarities - and differences - that make these two somewhat unrelated yeasts the dominant model systems for studying fundamental eukaryotic processes. Each of the nine chapters is an authoritative review written by experts in the field. The opening chapter surveys the technologies that have propelled efforts to elucidate the functions of the ~6000 predicted protein-encoding genes in S. cerevisiae; this chapter includes sections on bioinformatics, genome-wide transcription and proteome analysis. The next four chapters - covering DNA replication, the mitotic cell cycle, cell cycle checkpoints and nuclear division - form a well-integrated quartet that describes the complex molecular and genetic pathways governing faithful chromosome replication and segregation. The cell cycle chapter, in particular, is presented from a unique perspective: rather than focusing on the physiological changes that occur at each stage, it instead illustrates the molecular machines (i.e. the cyclin-dependent kinases) that propel the cell cycle. The fifth chapter provides a comprehensive discussion on RNA polymerase II transcription in S. cerevisiae that incorporates sections on general transcription factors, coactivators and repressors. It also includes a brief synopsis of the effects of chromatin on transcription, which creates a nice segue to the following chapter on the structure of chromatin at centromeres and telomeres. The final two chapters, on pre-mRNA splicing and nuclear transport of RNA and proteins, focus mainly on the mechanisms identified in budding yeast. The only obvious shortcoming with respect to the scope of this textbook is that it fails to include in-depth discussions of DNA repair and recombination. This publication has several attributes that make it an excellent reference source. First, it is a comprehensive review that weaves a great deal of supplementary information into each chapter. It not only is extensively referenced, but also frequently includes citations to reviews and to yeast database websites for further details. Second, the book is well written and readable. Each chapter is organized in a logical sequence - for example, the chapter on DNA replication starts with origin recognition and ends with Okazaki fragment processing. Furthermore, although the descriptions of genetic and molecular pathways are often encyclopedic, extensive summary tables and/or simple diagrams supplement the discussions and assist the reader in grasping the information. The value of such summary tables can be greatly appreciated when navigating through the maelstrom of mismatched S. cerevisiae and S. pombe CDC and RAD gene nomenclature. Lastly, there is an overall congruity that pulls together the topics of the separate chapters and relates them to one another. For instance, examples of genome-wide analyses are highlighted in several chapters to convey the practicality and usefulness of this approach, and the chapters on splicing and nuclear transport both include small sections that link these activities to other nuclear processes that have been discussed. It is important to note, however, that a complete understanding of many of the sections will require prior knowledge of fundamental genetic principles and molecular biology techniques; for this reason, the book may be better suited to the more advanced reader. The Yeast Nucleus is designed to stimulate thinking - not only about the similarities and differences between the budding and fission yeasts, but about whether comparable mechanisms might be used in other organisms as well. To achieve this goal, it goes beyond a comparative analysis of the two yeasts, and draws parallels with bacteriophage, viral and a variety of metazoan systems when applicable. The result is a well-integrated view that succeeds in providing a foundation for provoking thought about the unity of basic biological mechanisms. Moreover, each chapter concludes with an insightful look at the future direction of the field. In these regards, this publication will serve as a fabulous guidebook for experts as well as students.

2006 ◽  
Vol 5 (10) ◽  
pp. 1780-1787 ◽  
Author(s):  
Jeffrey Linger ◽  
Jessica K. Tyler

ABSTRACT The eukaryotic genome is packaged together with histone proteins into chromatin following DNA replication. Recent studies have shown that histones can also be assembled into chromatin independently of DNA replication and that this dynamic exchange of histones may be biased toward sites undergoing transcription. Here we show that epitope-tagged histone H4 can be incorporated into nucleosomes throughout the budding yeast (Saccharomyces cerevisiae) genome regardless of the phase of the cell cycle, the transcriptional status, or silencing of the region. Direct comparisons reveal that the amount of histone incorporation that occurs in G1-arrested cells is similar to that occurring in cells undergoing DNA replication. Additionally, we show that this histone incorporation is not dependent on the histone H3/H4 chaperones CAF-1, Asf1, and Hir1 individually. This study demonstrates that DNA replication and transcription are not necessary prerequisites for histone exchange in budding yeast, indicating that chromatin is more dynamic than previously thought.


2011 ◽  
Vol 22 (13) ◽  
pp. 2185-2197 ◽  
Author(s):  
Erica Raspelli ◽  
Corinne Cassani ◽  
Giovanna Lucchini ◽  
Roberta Fraschini

Timely down-regulation of the evolutionarily conserved protein kinase Swe1 plays an important role in cell cycle control, as Swe1 can block nuclear division through inhibitory phosphorylation of the catalytic subunit of cyclin-dependent kinase. In particular, Swe1 degradation is important for budding yeast cell survival in case of DNA replication stress, whereas it is inhibited by the morphogenesis checkpoint in response to alterations in actin cytoskeleton or septin structure. We show that the lack of the Dma1 and Dma2 ubiquitin ligases, which moderately affects Swe1 localization and degradation during an unperturbed cell cycle with no apparent phenotypic effects, is toxic for cells that are partially defective in Swe1 down-regulation. Moreover, Swe1 is stabilized, restrained at the bud neck, and hyperphosphorylated in dma1Δ dma2Δ cells subjected to DNA replication stress, indicating that the mechanism stabilizing Swe1 under these conditions is different from the one triggered by the morphogenesis checkpoint. Finally, the Dma proteins are required for proper Swe1 ubiquitylation. Taken together, the data highlight a previously unknown role of these proteins in the complex regulation of Swe1 and suggest that they might contribute to control, directly or indirectly, Swe1 ubiquitylation.


Author(s):  
Cory Haluska ◽  
Fengzhi Jin ◽  
Yanchang Wang

DNA replication stress activates the S-phase checkpoint that arrests the cell cycle, but it is poorly understood how cells recover from this arrest. Cyclin-dependent kinase (CDK) and Protein Phosphatase 2A (PP2A) are key cell cycle regulators, and Cdc55 is a regulatory subunit of PP2A in budding yeast. We found that yeast cells lacking functional PP2ACdc55 showed slow growth in the presence of hydroxyurea (HU), a DNA synthesis inhibitor, without obvious viability loss. Moreover, PP2A mutants exhibited delayed anaphase entry and sustained levels of anaphase inhibitor Pds1 after HU treatment. A DNA damage checkpoint Chk1 phosphorylates and stabilizes Pds1. We showed that chk1Δ and mutation of the Chk1 phosphorylation sites in Pds1 largely restored efficient anaphase entry in PP2A mutants after HU treatment. In addition, deletion of SWE1 that encodes the inhibitory kinase for CDK or mutation of the Swe1 phosphorylation site in CDK ( cdc28F19) also suppressed the anaphase entry delay in PP2A mutants after HU treatment. Our genetic data suggest that Swe1/CDK acts upstream of Pds1. Surprisingly, cdc55Δ showed significant suppression to the viability loss of S-phase checkpoint mutants during DNA synthesis block. Together, our results uncover a PP2A-Swe1-CDK-Chk1-Pds1 axis that promotes recovery from DNA replication stress.


2017 ◽  
Vol 2 ◽  
pp. 2 ◽  
Author(s):  
Colette Fox ◽  
Juan Zou ◽  
Juri Rappsilber ◽  
Adele L. Marston

Background Gametes are generated through a specialized cell division called meiosis, in which ploidy is reduced by half because two consecutive rounds of chromosome segregation, meiosis I and meiosis II, occur without intervening DNA replication. This contrasts with the mitotic cell cycle where DNA replication and chromosome segregation alternate to maintain the same ploidy. At the end of mitosis, CDKs are inactivated. This low CDK state in late mitosis/G1 allows for critical preparatory events for DNA replication and centrosome/spindle pole body (SPB) duplication. However, their execution is inhibited until S phase, where further preparatory events are also prevented. This “licensing” ensures that both the chromosomes and the centrosomes/SPBs replicate exactly once per cell cycle, thereby maintaining constant ploidy. Crucially, between meiosis I and meiosis II, centrosomes/SPBs must be re-licensed, but DNA re-replication must be avoided. In budding yeast, the Cdc14 protein phosphatase triggers CDK down regulation to promote exit from mitosis. Cdc14 also regulates the meiosis I to meiosis II transition, though its mode of action has remained unclear. Methods Fluorescence and electron microscopy was combined with proteomics to probe SPB duplication in cells with inactive or hyperactive Cdc14. Results We demonstrate that Cdc14 ensures two successive nuclear divisions by re-licensing SPBs at the meiosis I to meiosis II transition. We show that Cdc14 is asymmetrically enriched on a single SPB during anaphase I and provide evidence that this enrichment promotes SPB re-duplication. Cells with impaired Cdc14 activity fail to promote extension of the SPB half-bridge, the initial step in morphogenesis of a new SPB. Conversely, cells with hyper-active Cdc14 duplicate SPBs, but fail to induce their separation. Conclusion Our findings implicate reversal of key CDK-dependent phosphorylations in the differential licensing of cyclical events at the meiosis I to meiosis I transition.


1995 ◽  
Vol 129 (3) ◽  
pp. 739-749 ◽  
Author(s):  
D J Lew ◽  
S I Reed

Checkpoint controls are regulatory pathways that inhibit cell cycle progression in cells that have not faithfully completed a prior step in the cell cycle. In the budding yeast Saccharomyces cerevisiae, DNA replication and spindle assembly are monitored by checkpoint controls that prevent nuclear division in cells that have failed to complete these processes. During the normal cell cycle, bud formation is temporally coincident with DNA replication and spindle assembly, and the nucleus divides along the mother-bud axis in mitosis. In this report, we show that inhibition of bud formation also causes a dramatic delay in nuclear division. This allows cells to recover from a transient disruption of cell polarity without becoming binucleate. The delay occurs after DNA replication and spindle assembly, and results from delayed activation of the master cell cycle regulatory kinase, Cdc28. Cdc28 activation is inhibited by phosphorylation of Cdc28 on tyrosine 19, and by delayed accumulation of the B-type cyclins Clb1 and Clb2. These results suggest the existence of a novel checkpoint that monitors cell morphogenesis in budding yeast.


2020 ◽  
Author(s):  
Arun Mouli Kolinjivadi ◽  
Siao Ting Chong ◽  
Joanne Ngeow

Co-ordinated oscillation of mammalian circadian clock and cell cycle is essential for cellular and organismal homeostasis. Existing preclinical, epidemiological, molecular and biochemical evidence reveal a robust interplay between circadian clock, genome instability and cancer. Furthermore, recent investigations have demonstrated that the alterations in circadian clock perturb genome stability by modulating the cell cycle timing, altering DNA replication fork progression, influencing DNA Damage Response (DDR) and DNA repair efficiency. In this review, we examine the most recent findings from different eukaryotic model systems and discuss the functional interaction between circadian factors with key DNA replication, DDR and DNA repair genes.


1996 ◽  
Vol 109 (2) ◽  
pp. 319-326 ◽  
Author(s):  
N. Okishio ◽  
Y. Adachi ◽  
M. Yanagida

The nda1+ and nda4+ genes of the fission yeast Schizosaccharomyces pombe encode proteins similar to budding yeast MCM2 and MCM5/CDC46, respectively, which are required for the early stages of DNA replication. The budding yeast Mcm proteins display cell-cycle dependent localization. They are present in the nucleus specifically from late M phase until the beginning of S phase, so that they were suggested to be components of a replication licensing factor, a positive factor for the onset of replication, which is thought to be inactivated after use, thus restricting replication to only once in a cell cycle. In the present study, we raised antibodies against Nda1 or Nda4 and identified 115 kDa and 80 kDa proteins, respectively. Their immunolocalization was examined in wild-type cells and in various cell-cycle mutants. Both Nda1 and Nda4 proteins remained primarily in the nucleus throughout the cell cycle. In mutants arrested in G1, S, and G2 phases, these proteins were also enriched in the nucleus. These results indicate that the dramatic change in subcellular localization as seen in budding yeast is not essential in fission yeast for the functions of Nda1 and Nda4 proteins to be executed. The histidine-tagged nda1+ gene was constructed and integrated into the chromosome to replace the wild-type nda1+ gene. The resulting His-tagged Nda1 protein was adsorbed to the Ni-affinity column, and co-eluted with the untagged Nda4 protein, suggesting that they formed a complex.


2007 ◽  
Vol 18 (8) ◽  
pp. 2805-2816 ◽  
Author(s):  
Lina Ma ◽  
Jennifer McQueen ◽  
Lara Cuschieri ◽  
Jackie Vogel ◽  
Vivien Measday

The kinetochore, a protein complex that links chromosomes to microtubules (MTs), is required to prevent spindle expansion during S phase in budding yeast, but the mechanism of how the kinetochore maintains integrity of the bipolar spindle before mitosis is not well understood. Here, we demonstrate that a mutation of Spc24, a component of the conserved Ndc80 kinetochore complex, causes lethality when cells are exposed to the DNA replication inhibitor hydroxyurea (HU) due to premature spindle expansion and segregation of incompletely replicated DNA. Overexpression of Stu1, a CLASP-related MT-associated protein or a truncated form of the XMAP215 orthologue Stu2 rescues spc24-9 HU lethality and prevents spindle expansion. Truncated Stu2 likely acts in a dominant-negative manner, because overexpression of full-length STU2 does not rescue spc24-9 HU lethality, and spindle expansion in spc24-9 HU-treated cells requires active Stu2. Stu1 and Stu2 localize to the kinetochore early in the cell cycle and Stu2 kinetochore localization depends on Spc24. We propose that mislocalization of Stu2 results in premature spindle expansion in S phase stalled spc24-9 mutants. Identifying factors that restrain spindle expansion upon inhibition of DNA replication is likely applicable to the mechanism by which spindle elongation is regulated during a normal cell cycle.


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