301
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Tanaka T, Fuchs J, Loidl J, Nasmyth K. Cohesin ensures bipolar attachment of microtubules to sister centromeres and resists their precocious separation. Nat Cell Biol 2000; 2:492-9. [PMID: 10934469 DOI: 10.1038/35019529] [Citation(s) in RCA: 255] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
The multisubunit protein complex cohesin is required to establish cohesion between sister chromatids during S phase and to maintain it during G2 and M phases. Cohesin is essential for mitosis, and even partial defects cause very high rates of chromosome loss. In budding yeast, cohesin associates with specific sites which are distributed along the entire length of a chromosome but are more dense in the vicinity of the centromere. Real-time imaging of individual centromeres tagged with green fluorescent protein suggests that cohesin bound to centromeres is important for bipolar attachment to microtubules. This cohesin is, however, incapable of resisting the consequent force, which leads to sister centromere splitting and chromosome stretching. Meanwhile, cohesin bound to sequences flanking the centromeres prevents sister chromatids from completely unzipping and is required to pull back together sister centromeres that have already split. Cohesin therefore has a central role in generating a dynamic tension between microtubules and sister chromatid cohesion at centromeres, which lasts until chromosome segregation is finally promoted by separin-dependent cleavage of the cohesin subunit Scc1p.
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Affiliation(s)
- T Tanaka
- Research Institute of Molecular Pathology, Dr Bohr-Gasse 7, A-1030 Vienna, Austria
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302
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Shonn MA, McCarroll R, Murray AW. Requirement of the spindle checkpoint for proper chromosome segregation in budding yeast meiosis. Science 2000; 289:300-3. [PMID: 10894778 DOI: 10.1126/science.289.5477.300] [Citation(s) in RCA: 177] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The spindle checkpoint was characterized in meiosis of budding yeast. In the absence of the checkpoint, the frequency of meiosis I missegregation increased with increasing chromosome length, reaching 19% for the longest chromosome. Meiosis I nondisjunction in spindle checkpoint mutants could be prevented by delaying the onset of anaphase. In a recombination-defective mutant (spo11Delta), the checkpoint delays the biochemical events of anaphase I, suggesting that chromosomes that are attached to microtubules but are not under tension can activate the spindle checkpoint. Spindle checkpoint mutants reduce the accuracy of chromosome segregation in meiosis I much more than that in meiosis II, suggesting that checkpoint defects may contribute to Down syndrome.
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Affiliation(s)
- M A Shonn
- Department of Biochemistry and Department of Physiology, University of California, San Francisco, CA 94143-0444, USA
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303
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He X, Asthana S, Sorger PK. Transient sister chromatid separation and elastic deformation of chromosomes during mitosis in budding yeast. Cell 2000; 101:763-75. [PMID: 10892747 DOI: 10.1016/s0092-8674(00)80888-0] [Citation(s) in RCA: 228] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022]
Abstract
The accurate segregation of chromosomes at mitosis requires that all pairs of chromatids bind correctly to microtubules prior to the dissolution of sister cohesion and the initiation of anaphase. By analyzing the motion of GFP-tagged S. cerevisiae chromosomes, we show that kinetochore-microtubule attachments impose sufficient tension on sisters during prometaphase to transiently separate centromeric chromatin toward opposite sides of the spindle. Transient separations of 2-10 min duration occur in the absence of cohesin proteolysis, are characterized by independent motion of the sisters along the spindle, and are followed by the apparent reestablishment of sister linkages. The existence of transient sister separation in yeast explains the unusual bilobed localization of kinetochore proteins and supports an alternative model for spindle structure. By analogy with animal cells, we propose that yeast centromeric chromatin acts as a tensiometer.
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Affiliation(s)
- X He
- Massachusetts Institute of Technology, Department of Biology, Cambridge 02139, USA
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304
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Wein H, Bass HW, Cande WZ. DSK1, a kinesin-related protein involved in anaphase spindle elongation, is a component of a mitotic spindle matrix. CELL MOTILITY AND THE CYTOSKELETON 2000; 41:214-24. [PMID: 9829776 DOI: 10.1002/(sici)1097-0169(1998)41:3<214::aid-cm3>3.0.co;2-p] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Abstract
DSK1 is a kinesin-related protein that is involved in anaphase spindle elongation in the diatom Cylindrotheca fuisiformis [Wein et al., 1996: J. Cell Biol. 113:595-604]. DSK1 staining appeared to be concentrated in the gap that forms as the two half-spindles separate, suggesting that DSK1 may be part of a non-microtubule spindle matrix. We set out to investigate this possibility using three-dimensional high-resolution fluorescence microscopy, and biochemical methods of tubulin extraction. Three-dimensional fluorescence microscopy reveals that DSK1 remains in the midzone after the bulk of the microtubules from the two half-spindles have left the region. Biochemical studies show that CaCl2 extraction of tubulin from a mitotic spindle preparation does not extract similar proportions of DSK1 protein. Immunofluorescence confirms that this CaCl2 extraction leaves behind spindle-like bars that are recognized by anti-DSK1, but not by anti-tubulin antibodies. We conclude that DSK1 is part of, or attached to, a non-microtubule scaffold in the diatom central spindle. This discovery has implications for both the structural organization of the mitotic spindle and the mechanism of spindle elongation.
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Affiliation(s)
- H Wein
- Federation of American Scientists, Washington, DC, USA
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305
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Abstract
On monocentric chromosomes the centromere is the chromosomal site at which the kinetochore complex is assembled. This complex mediates the attachment and movement of chromosomes along spindle microtubules. The centromere is usually the last site to retain cohesion between sister centromeres. The location of the main sensor for defective spindle assembly at the kinetochore allows the release of this cohesion, and thus progression through mitosis, to be held in check until key events have been completed. The intricate nature of the centromere-kinetochore complexes and the events they co-ordinate and react to is presently being dissected by studies in several organisms. In particular, several new kinetochore proteins have been identified in many organisms over the last year.
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Affiliation(s)
- A L Pidoux
- Human Genetics Unit, Medical Research Council, Western General Hospital, Edinburgh, EH4 2XU, UK.
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306
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Jin QW, Fuchs J, Loidl J. Centromere clustering is a major determinant of yeast interphase nuclear organization. J Cell Sci 2000; 113 ( Pt 11):1903-12. [PMID: 10806101 DOI: 10.1242/jcs.113.11.1903] [Citation(s) in RCA: 170] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
During interphase in the budding yeast, Saccharomyces cerevisiae, centromeres are clustered near one pole of the nucleus as a rosette with the spindle pole body at its hub. Opposite to the centromeric pole is the nucleolus. Chromosome arms extend outwards from the centromeric pole and are preferentially directed towards the opposite pole. Centromere clustering is reduced by the ndc10 mutation, which affects a kinetochore protein, and by the microtubule poison nocodazole. This suggests that clustering is actively maintained or enforced by the association of centromeres with microtubules throughout interphase. Unlike the Rabl-orientation known from many higher eukaryotes, centromere clustering in yeast is not only a relic of anaphase chromosome polarization, because it can be reconstituted without the passage of cells through anaphase. Within the rosette, homologous centromeres are not arranged in a particular order that would suggest somatic pairing or genome separation.
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Affiliation(s)
- Q W Jin
- Institute of Botany, University of Vienna, Rennweg 14, A-1030 Vienna, Austria
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307
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Lin H, Choi JH, Hasek J, DeLillo N, Lou W, Vancura A. Phospholipase C is involved in kinetochore function in Saccharomyces cerevisiae. Mol Cell Biol 2000; 20:3597-607. [PMID: 10779349 PMCID: PMC85652 DOI: 10.1128/mcb.20.10.3597-3607.2000] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The budding yeast PLC1 gene encodes a homolog of the delta isoform of mammalian phosphoinositide-specific phospholipase C. Here, we present evidence that Plc1p associates with the kinetochore complex CBF3. This association is mediated through interactions with two established kinetochore proteins, Ndc10p and Cep3p. We show by chromatin immunoprecipitation experiments that Plc1p resides at centromeric loci in vivo. Deletion of PLC1, as well as plc1 mutations which abrogate the interaction of Plc1p with the CBF3 complex, results in a higher frequency of minichromosome loss, nocodazole sensitivity, and mitotic delay. Overexpression of Ndc10p suppresses the nocodazole sensitivity of plc1 mutants, implying that the association of Plc1p with CBF3 is important for optimal kinetochore function. Chromatin extracts from plc1Delta cells exhibit reduced microtubule binding to minichromosomes. These results suggest that Plc1p associates with kinetochores and regulates some aspect of kinetochore function and demonstrate an intranuclear function of phospholipase C in eukaryotic cells.
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Affiliation(s)
- H Lin
- Department of Biological Sciences, St. John's University, Jamaica, New York 11439, USA
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308
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Abstract
The budding yeast Saccharomyces cerevisiae provides a unique opportunity for study of the microtubule-based motor proteins that participate in mitotic spindle function. The genome of Saccharomyces encodes a relatively small and genetically tractable set of microtubule-based motor proteins. The single cytoplasmic dynein and five of the six kinesin-related proteins encoded have been implicated in mitotic spindle function. Each motor protein is unique in amino acid sequence. On account of functional overlap, no single motor is uniquely required for cell viability, however. The ability to create and analyze multiple mutants has allowed experimental dissection of the roles performed by each mitotic motor. Some of the motors operate within the nucleus to assemble and elongate the bipolar spindle (kinesin-related Cin8p, Kip1p, Kip3p and Kar3p). Others operate on the cytoplasmic microtubules to effect spindle and nuclear positioning within the cell (dynein and kinesin-related Kip2p, Kip3p and Kar3p). The six motors apparently contribute three fundamental activities to spindle function: motility, microtubule cross-linking and regulation of microtubule dynamics.
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Affiliation(s)
- E R Hildebrandt
- Department of Biology, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218, USA
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309
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Goshima G, Yanagida M. Establishing biorientation occurs with precocious separation of the sister kinetochores, but not the arms, in the early spindle of budding yeast. Cell 2000; 100:619-33. [PMID: 10761928 DOI: 10.1016/s0092-8674(00)80699-6] [Citation(s) in RCA: 243] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Sister kinetochores are bioriented toward the spindle poles in higher eukaryotic prometaphase before chromosome segregation. We show that, in budding yeast, the sister kinetochores are separated in the very early spindle, while the sister arms remain associated. Biorientation of the separated kinetochores is achieved already after replication. Mtw1p, a homolog of fission yeast Mis12 required for biorientation, locates at the centromeres in an Ndc10p-dependent manner. Mtw1p and the sequences 1.8 and 3.8 kb from CEN3 and CEN15, respectively, behave like the precociously separated kinetochores, whereas the sequences 23 and 35 kb distant from CEN3 and CEN5 previously used as the centromere markers behave like a part of the arm. Mtw1p and Ndc10p are identically located except for additional spindle localization of Ndc10p. A model explaining small centromeres and early spindle formation in budding yeast is proposed.
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Affiliation(s)
- G Goshima
- CREST Research Project, Department of Biophysics, Graduate School of Science, Kyoto University, Japan
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310
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Maddox PS, Bloom KS, Salmon ED. The polarity and dynamics of microtubule assembly in the budding yeast Saccharomyces cerevisiae. Nat Cell Biol 2000; 2:36-41. [PMID: 10620805 PMCID: PMC2879060 DOI: 10.1038/71357] [Citation(s) in RCA: 198] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Microtubule assembly in Saccharomyces cerevisiae is initiated from sites within spindle pole bodies (SPBs) in the nuclear envelope. Microtubule plus ends are thought to be organized distal to the SPBs, while minus ends are proximal. Several hypotheses for the function of microtubule motor proteins in force generation and regulation of microtubule assembly propose that assembly and disassembly occur at minus ends as well as at plus ends. Here we analyse microtubule assembly relative to the SPBs in haploid yeast cells expressing green fluorescent protein fused to alpha-tubulin, a microtubule subunit. Throughout the cell cycle, analysis of fluorescent speckle marks on cytoplasmic astral microtubules reveals that there is no detectable assembly or disassembly at minus ends. After laser-photobleaching, metaphase spindles recover about 63% of the bleached fluorescence, with a half-life of about 1 minute. After anaphase onset, photobleached marks in the interpolar spindle are persistent and do not move relative to the SPBs. In late anaphase, the elongated spindles disassemble at the microtubule plus ends. These results show for astral and anaphase interpolar spindle microtubules, and possibly for metaphase spindle microtubules, that microtubule assembly and disassembly occur at plus, and not minus, ends.
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Affiliation(s)
- P S Maddox
- Department of Biology, CB3280, University of North Carolina, Chapel Hill, North Carolina 27599-3280, USA.
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311
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Gordon DM, Roof DM. The kinesin-related protein Kip1p of Saccharomyces cerevisiae is bipolar. J Biol Chem 1999; 274:28779-86. [PMID: 10497250 DOI: 10.1074/jbc.274.40.28779] [Citation(s) in RCA: 45] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Kip1p is a mitotic spindle-associated kinesin-related protein in Saccharomyces cerevisiae that participates in spindle pole separation. Here, we define the domain arrangement and polypeptide composition of the Kip1p holoenzyme. Electron microscopy of rotary shadowed Kip1p molecules revealed two globular domains 14 nm in diameter connected by a 73-nm long stalk. When the Kip1p domain homologous to the kinesin motor domain was decorated with an unrelated protein, the diameter of the globular domains at both ends of the stalk increased, indicating that Kip1p is bipolar. Soluble Kip1p isolated from S. cerevisiae cells was homomeric, based on the similarity of the sedimentation coefficients of native Kip1p from S. cerevisiae and Kip1p which was purified after expression in insect cells. The holoenzyme molecular weight was estimated using the sedimentation coefficient and Stokes radius, and was most consistent with a tetrameric composition. Kip1p exhibited an ionic strength-dependent transition in its sedimentation coefficient, revealing a potential regulatory mechanism. The position of kinesin motor-related domains at each end of the stalk may allow Kip1p to cross-link either parallel or antiparallel microtubules during mitotic spindle assembly and pole separation.
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Affiliation(s)
- D M Gordon
- Department of Physiology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6085, USA
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312
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Zeng X, Kahana JA, Silver PA, Morphew MK, McIntosh JR, Fitch IT, Carbon J, Saunders WS. Slk19p is a centromere protein that functions to stabilize mitotic spindles. J Cell Biol 1999; 146:415-25. [PMID: 10427094 PMCID: PMC3206577 DOI: 10.1083/jcb.146.2.415] [Citation(s) in RCA: 117] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/1999] [Accepted: 06/21/1999] [Indexed: 11/30/2022] Open
Abstract
We have identified a novel centromere-associated gene product from Saccharomyces cerevisiae that plays a role in spindle assembly and stability. Strains with a deletion of SLK19 (synthetic lethal Kar3p gene) exhibit abnormally short mitotic spindles, increased numbers of astral microtubules, and require the presence of the kinesin motor Kar3p for viability. When cells are deprived of both Slk19p and Kar3p, rapid spindle breakdown and mitotic arrest is observed. A functional fusion of Slk19p to green fluorescent protein (GFP) localizes to kinetochores and, during anaphase, to the spindle midzone, whereas Kar3p-GFP was found at the nuclear side of the spindle pole body. Thus, these proteins seem to play overlapping roles in stabilizing spindle structure while acting from opposite ends of the microtubules.
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Affiliation(s)
- X Zeng
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA
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313
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Jones MH, Bachant JB, Castillo AR, Giddings TH, Winey M. Yeast Dam1p is required to maintain spindle integrity during mitosis and interacts with the Mps1p kinase. Mol Biol Cell 1999; 10:2377-91. [PMID: 10397771 PMCID: PMC25456 DOI: 10.1091/mbc.10.7.2377] [Citation(s) in RCA: 62] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
We have identified a mutant allele of the DAM1 gene in a screen for mutations that are lethal in combination with the mps1-1 mutation. MPS1 encodes an essential protein kinase that is required for duplication of the spindle pole body and for the spindle assembly checkpoint. Mutations in six different genes were found to be lethal in combination with mps1-1, of which only DAM1 was novel. The remaining genes encode a checkpoint protein, Bub1p, and four chaperone proteins, Sti1p, Hsc82p, Cdc37p, and Ydj1p. DAM1 is an essential gene that encodes a protein recently described as a member of a microtubule binding complex. We report here that cells harboring the dam1-1 mutation fail to maintain spindle integrity during anaphase at the restrictive temperature. Consistent with this phenotype, DAM1 displays genetic interactions with STU1, CIN8, and KAR3, genes encoding proteins involved in spindle function. We have observed that a Dam1p-Myc fusion protein expressed at endogenous levels and localized by immunofluorescence microscopy, appears to be evenly distributed along short mitotic spindles but is found at the spindle poles at later times in mitosis.
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Affiliation(s)
- M H Jones
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado-Boulder, Boulder Colorado 80309-0347, USA
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314
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Muñoz-Centeno MC, McBratney S, Monterrosa A, Byers B, Mann C, Winey M. Saccharomyces cerevisiae MPS2 encodes a membrane protein localized at the spindle pole body and the nuclear envelope. Mol Biol Cell 1999; 10:2393-406. [PMID: 10397772 PMCID: PMC25459 DOI: 10.1091/mbc.10.7.2393] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The MPS2 (monopolar spindle two) gene is one of several genes required for the proper execution of spindle pole body (SPB) duplication in the budding yeast Saccharomyces cerevisiae (). We report here that the MPS2 gene encodes an essential 44-kDa protein with two putative coiled-coil regions and a hydrophobic sequence. Although MPS2 is required for normal mitotic growth, some null strains can survive; these survivors exhibit slow growth and abnormal ploidy. The MPS2 protein was tagged with nine copies of the myc epitope, and biochemical fractionation experiments show that it is an integral membrane protein. Visualization of a green fluorescent protein (GFP) Mps2p fusion protein in living cells and indirect immunofluorescence microscopy of 9xmyc-Mps2p revealed a perinuclear localization with one or two brighter foci of staining corresponding to the SPB. Additionally, immunoelectron microscopy shows that GFP-Mps2p localizes to the SPB. Our analysis suggests that Mps2p is required as a component of the SPB for insertion of the nascent SPB into the nuclear envelope.
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Affiliation(s)
- M C Muñoz-Centeno
- Service de Biochimie et de Génétique Moléculaire, Commissariat à l'Energie Atomique/Saclay, F-91191 Gif-sur-Yvette, France
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315
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Kim JH, Kang JS, Chan CS. Sli15 associates with the ipl1 protein kinase to promote proper chromosome segregation in Saccharomyces cerevisiae. J Biophys Biochem Cytol 1999; 145:1381-94. [PMID: 10385519 PMCID: PMC2133162 DOI: 10.1083/jcb.145.7.1381] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
The conserved Ipl1 protein kinase is essential for proper chromosome segregation and thus cell viability in the budding yeast Saccharomyces cerevisiae. Its human homologue has been implicated in the tumorigenesis of diverse forms of cancer. We show here that sister chromatids that have separated from each other are not properly segregated to opposite poles of ipl1-2 cells. Failures in chromosome segregation are often associated with abnormal distribution of the spindle pole-associated Nuf2-GFP protein, thus suggesting a link between potential spindle pole defects and chromosome missegregation in ipl1 mutant cells. A small fraction of ipl1-2 cells also appears to be defective in nuclear migration or bipolar spindle formation. Ipl1 associates, probably directly, with the novel and essential Sli15 protein in vivo, and both proteins are localized to the mitotic spindle. Conditional sli15 mutant cells have cytological phenotypes very similar to those of ipl1 cells, and the ipl1-2 mutation exhibits synthetic lethal genetic interaction with sli15 mutations. sli15 mutant phenotype, like ipl1 mutant phenotype, is partially suppressed by perturbations that reduce protein phosphatase 1 function. These genetic and biochemical studies indicate that Sli15 associates with Ipl1 to promote its function in chromosome segregation.
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Affiliation(s)
- J H Kim
- Department of Microbiology and Institute for Cellular and Molecular Biology, The University of Texas, Austin, Texas 78712, USA
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316
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O'Toole ET, Winey M, McIntosh JR. High-voltage electron tomography of spindle pole bodies and early mitotic spindles in the yeast Saccharomyces cerevisiae. Mol Biol Cell 1999; 10:2017-31. [PMID: 10359612 PMCID: PMC25406 DOI: 10.1091/mbc.10.6.2017] [Citation(s) in RCA: 245] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The spindle pole body (SPB) is the major microtubule-organizing center of budding yeast and is the functional equivalent of the centrosome in higher eukaryotic cells. We used fast-frozen, freeze-substituted cells in conjunction with high-voltage electron tomography to study the fine structure of the SPB and the events of early spindle formation. Individual structures were imaged at 5-10 nm resolution in three dimensions, significantly better than can be achieved by serial section electron microscopy. The SPB is organized in distinct but coupled layers, two of which show ordered two-dimensional packing. The SPB central plaque is anchored in the nuclear envelope with hook-like structures. The minus ends of nuclear microtubules (MTs) are capped and are tethered to the SPB inner plaque, whereas the majority of MT plus ends show a distinct flaring. Unbudded cells containing a single SPB retain 16 MTs, enough to attach to each of the expected 16 chromosomes. Their median length is approximately 150 nm. MTs growing from duplicated but not separated SPBs have a median length of approximately 130 nm and interdigitate over the bridge that connects the SPBs. As a bipolar spindle is formed, the median MT length increases to approximately 300 nm and then decreases to approximately 30 nm in late anaphase. Three-dimensional models confirm that there is no conventional metaphase and that anaphase A occurs. These studies complement and extend what is known about the three-dimensional structure of the yeast mitotic spindle and further our understanding of the organization of the SPB in intact cells.
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Affiliation(s)
- E T O'Toole
- Boulder Laboratory for Three-dimensional Fine Structure, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347, USA.
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317
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Tirnauer JS, O'Toole E, Berrueta L, Bierer BE, Pellman D. Yeast Bim1p promotes the G1-specific dynamics of microtubules. J Biophys Biochem Cytol 1999; 145:993-1007. [PMID: 10352017 PMCID: PMC2133138 DOI: 10.1083/jcb.145.5.993] [Citation(s) in RCA: 210] [Impact Index Per Article: 8.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Microtubule dynamics vary during the cell cycle, and microtubules appear to be more dynamic in vivo than in vitro. Proteins that promote dynamic instability are therefore central to microtubule behavior in living cells. Here, we report that a yeast protein of the highly conserved EB1 family, Bim1p, promotes cytoplasmic microtubule dynamics specifically during G1. During G1, microtubules in cells lacking BIM1 showed reduced dynamicity due to a slower shrinkage rate, fewer rescues and catastrophes, and more time spent in an attenuated/paused state. Human EB1 was identified as an interacting partner for the adenomatous polyposis coli (APC) tumor suppressor protein. Like human EB1, Bim1p localizes to dots at the distal ends of cytoplasmic microtubules. This localization, together with data from electron microscopy and a synthetic interaction with the gene encoding the kinesin Kar3p, suggests that Bim1p acts at the microtubule plus end. Our in vivo data provide evidence of a cell cycle-specific microtubule-binding protein that promotes microtubule dynamicity.
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Affiliation(s)
- J S Tirnauer
- Department of Pediatric Oncology, Dana-Farber Cancer Institute, Boston, MA, USA
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318
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Feierbach B, Nogales E, Downing KH, Stearns T. Alf1p, a CLIP-170 domain-containing protein, is functionally and physically associated with alpha-tubulin. J Cell Biol 1999; 144:113-24. [PMID: 9885248 PMCID: PMC2148126 DOI: 10.1083/jcb.144.1.113] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/1998] [Revised: 12/07/1998] [Indexed: 11/25/2022] Open
Abstract
Tubulin is a heterodimer of alpha- and beta-tubulin polypeptides. Assembly of the tubulin heterodimer in vitro requires the CCT chaperonin complex, and a set of five proteins referred to as the tubulin cofactors (Tian, F., Y. Huang, H. Rommelaere, J. Vandekerckhove, C. Ampe, and N.J. Cowan. 1996. Cell. 86:287-296; Tian, G., S.A. Lewis, B. Feierbach, T. Stearns, H. Rommelaere, C. Ampe, and N.J. Cowan. 1997. J. Cell Biol. 138:821-832). We report the characterization of Alf1p, the yeast ortholog of mammalian cofactor B. Alf1p interacts with alpha-tubulin in both two-hybrid and immunoprecipitation assays. Alf1p and cofactor B contain a single CLIP-170 domain, which is found in several microtubule-associated proteins. Mutation of the CLIP-170 domain in Alf1p disrupts the interaction with alpha-tubulin. Mutations in alpha-tubulin that disrupt the interaction with Alf1p map to a domain on the cytoplasmic face of alpha-tubulin; this domain is distinct from the region of interaction between alpha-tubulin and beta-tubulin. Alf1p-green fluorescent protein (GFP) is able to associate with microtubules in vivo, and this localization is abolished either by mutation of the CLIP-170 domain in Alf1p, or by mutation of the Alf1p-binding domain in alpha-tubulin. Analysis of double mutants constructed between null alleles of ALF1 and PAC2, which encodes the other yeast alpha-tubulin cofactor, suggests that Alf1p and Pac2p act in the same pathway leading to functional alpha-tubulin. The phenotype of overexpression of ALF1 suggests that Alf1p can act to sequester alpha-tubulin from interaction with beta-tubulin, raising the possibility that it plays a regulatory role in the formation of the tubulin heterodimer.
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Affiliation(s)
- B Feierbach
- Department of Biological Sciences, Stanford University, Stanford, California 94305-5020, USA
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319
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Sharp DJ, McDonald KL, Brown HM, Matthies HJ, Walczak C, Vale RD, Mitchison TJ, Scholey JM. The bipolar kinesin, KLP61F, cross-links microtubules within interpolar microtubule bundles of Drosophila embryonic mitotic spindles. J Cell Biol 1999; 144:125-38. [PMID: 9885249 PMCID: PMC2148119 DOI: 10.1083/jcb.144.1.125] [Citation(s) in RCA: 247] [Impact Index Per Article: 9.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/19/1998] [Revised: 11/30/1998] [Indexed: 11/22/2022] Open
Abstract
Previous genetic and biochemical studies have led to the hypothesis that the essential mitotic bipolar kinesin, KLP61F, cross-links and slides microtubules (MTs) during spindle assembly and function. Here, we have tested this hypothesis by immunofluorescence and immunoelectron microscopy (immunoEM). We show that Drosophila embryonic spindles at metaphase and anaphase contain abundant bundles of MTs running between the spindle poles. These interpolar MT bundles are parallel near the poles and antiparallel in the midzone. We have observed that KLP61F motors, phosphorylated at a cdk1/cyclin B consensus domain within the BimC box (BCB), localize along the length of these interpolar MT bundles, being concentrated in the midzone region. Nonphosphorylated KLP61F motors, in contrast, are excluded from the spindle and display a cytoplasmic localization. Immunoelectron microscopy further suggested that phospho-KLP61F motors form cross-links between MTs within interpolar MT bundles. These bipolar KLP61F MT-MT cross-links should be capable of organizing parallel MTs into bundles within half spindles and sliding antiparallel MTs apart in the spindle midzone. Thus we propose that bipolar kinesin motors and MTs interact by a "sliding filament mechanism" during the formation and function of the mitotic spindle.
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Affiliation(s)
- D J Sharp
- Section of Molecular and Cellular Biology, University of California Davis, Davis, California 95616, USA
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320
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Chial HJ, Rout MP, Giddings TH, Winey M. Saccharomyces cerevisiae Ndc1p is a shared component of nuclear pore complexes and spindle pole bodies. J Cell Biol 1998; 143:1789-800. [PMID: 9864355 PMCID: PMC2175219 DOI: 10.1083/jcb.143.7.1789] [Citation(s) in RCA: 118] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/1998] [Revised: 11/12/1998] [Indexed: 11/22/2022] Open
Abstract
We report a novel connection between nuclear pore complexes (NPCs) and spindle pole bodies (SPBs) revealed by our studies of the Saccharomyces cerevisiae NDC1 gene. Although both NPCs and SPBs are embedded in the nuclear envelope (NE) in yeast, their known functions are quite distinct. Previous work demonstrated that NDC1 function is required for proper SPB duplication (Winey, M., M.A. Hoyt, C. Chan, L. Goetsch, D. Botstein, and B. Byers. 1993. J. Cell Biol. 122:743-751). Here, we show that Ndc1p is a membrane protein of the NE that localizes to both NPCs and SPBs. Indirect immunofluorescence microscopy shows that Ndc1p displays punctate, nuclear peripheral localization that colocalizes with a known NPC component, Nup49p. Additionally, distinct spots of Ndc1p localization colocalize with a known SPB component, Spc42p. Immunoelectron microscopy shows that Ndc1p localizes to the regions of NPCs and SPBs that interact with the NE. The NPCs in ndc1-1 mutant cells appear to function normally at the nonpermissive temperature. Finally, we have found that a deletion of POM152, which encodes an abundant but nonessential nucleoporin, suppresses the SPB duplication defect associated with a mutation in the NDC1 gene. We show that Ndc1p is a shared component of NPCs and SPBs and propose a shared function in the assembly of these organelles into the NE.
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Affiliation(s)
- H J Chial
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado-Boulder, Boulder, Colorado 80309-0347, USA
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321
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Salmon ED, Yeh E, Shaw S, Skibbens B, Bloom K. High-resolution video and digital-enhanced differential interference contrast light microscopy of cell division in budding yeast. Methods Enzymol 1998; 298:317-31. [PMID: 9751891 DOI: 10.1016/s0076-6879(98)98028-4] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Affiliation(s)
- E D Salmon
- Department of Cell Biology, Duke University Medical Center, Durham, North Carolina 27710, USA
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322
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Maney T, Hunter AW, Wagenbach M, Wordeman L. Mitotic centromere-associated kinesin is important for anaphase chromosome segregation. J Cell Biol 1998; 142:787-801. [PMID: 9700166 PMCID: PMC2148171 DOI: 10.1083/jcb.142.3.787] [Citation(s) in RCA: 235] [Impact Index Per Article: 9.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023] Open
Abstract
Mitotic centromere-associated kinesin (MCAK) is recruited to the centromere at prophase and remains centromere associated until after telophase. MCAK is a homodimer that is encoded by a single gene and has no associated subunits. A motorless version of MCAK that binds centromeres but not microtubules disrupts chromosome segregation during anaphase. Antisense-induced depletion of MCAK results in the same defect. MCAK overexpression induces centromere-independent bundling and eventual loss of spindle microtubule polymer suggesting that centromere-associated bundling and/or depolymerization activity is required for anaphase. Live cell imaging indicates that MCAK may be required to coordinate the onset of sister centromere separation.
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Affiliation(s)
- T Maney
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98195, USA
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323
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Gull K, Alsford S, Ersfeld K. Segregation of minichromosomes in trypanosomes: implications for mitotic mechanisms. Trends Microbiol 1998; 6:319-23. [PMID: 9746942 DOI: 10.1016/s0966-842x(98)01314-6] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/08/2023]
Abstract
In addition to 11 pairs of housekeeping chromosomes, the genome of Trypanosoma brucei contains approximately 100 minichromosomes that are probably involved in the ability of the parasite to evade the host's immune response. This minichromosomal population is segregated on the mitotic spindle. How this is achieved provides insight into potential segregation mechanisms for small DNA molecules in eukaryotic microorganisms.
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Affiliation(s)
- K Gull
- School of Biological Sciences, University of Manchester, UK.
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324
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Abstract
Spindle poles are discernible by light microscopy as the sites where microtubules converge at the ends of both mitotic and meiotic spindles. In most cell types centrosomes are present at spindle poles due to their dominant role in microtubule nucleation. However, in some specialized cell types microtubules converge into spindle poles in the absence of centrosomes. Thus, spindle poles in centrosomal and acentrosomal cell types are structurally different, and it is this structural dichotomy that has created confusion as to the mechanism by which microtubules are organized into spindle poles. This review summarizes a series of recent articles that begin to resolve this confusion by demonstrating that spindle poles are organized through a common mechanism by a conserved group of non-centrosomal proteins in the presence or absence of centrosomes.
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Affiliation(s)
- D A Compton
- Department of Biochemistry, Dartmouth Medical School, Room 411, Hanover, NH 03755, USA.
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325
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Wigge PA, Jensen ON, Holmes S, Souès S, Mann M, Kilmartin JV. Analysis of the Saccharomyces spindle pole by matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. J Cell Biol 1998; 141:967-77. [PMID: 9585415 PMCID: PMC2132767 DOI: 10.1083/jcb.141.4.967] [Citation(s) in RCA: 265] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
A highly enriched spindle pole preparation was prepared from budding yeast and fractionated by SDS gel electrophoresis. Forty-five of the gel bands that appeared enriched in this fraction were analyzed by high-mass accuracy matrix-assisted laser desorption/ ionization (MALDI) peptide mass mapping combined with sequence database searching. This identified twelve of the known spindle pole components and an additional eleven gene products that had not previously been localized to the spindle pole. Immunoelectron microscopy localized eight of these components to different parts of the spindle. One of the gene products, Ndc80p, shows homology to human HEC protein (Chen, Y., D.J. Riley, P-L. Chen, and W-H. Lee. 1997. Mol. Cell Biol. 17:6049-6056) and temperature-sensitive mutants show defects in chromosome segregation. This is the first report of the identification of the components of a large cellular organelle by MALDI peptide mapping alone.
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MESH Headings
- Amino Acid Sequence
- Chromosomes, Fungal/physiology
- Chromosomes, Fungal/ultrastructure
- Cloning, Molecular
- Cytoskeletal Proteins
- Databases, Factual
- Humans
- Kinetochores
- Microscopy, Immunoelectron
- Models, Biological
- Molecular Sequence Data
- Mutagenesis, Site-Directed
- Neoplasm Proteins/chemistry
- Nuclear Proteins/analysis
- Nuclear Proteins/biosynthesis
- Nuclear Proteins/chemistry
- Peptide Library
- Peptide Mapping
- Saccharomyces cerevisiae/physiology
- Saccharomyces cerevisiae/ultrastructure
- Saccharomyces cerevisiae Proteins
- Schizosaccharomyces
- Sequence Alignment
- Sequence Homology, Amino Acid
- Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization/methods
- Spindle Apparatus/physiology
- Spindle Apparatus/ultrastructure
- Temperature
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Affiliation(s)
- P A Wigge
- Medical Research Council (MRC) Laboratory of Molecular Biology, Cambridge CB2 2QH, United Kingdom
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326
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Huyett A, Kahana J, Silver P, Zeng X, Saunders WS. The Kar3p and Kip2p motors function antagonistically at the spindle poles to influence cytoplasmic microtubule numbers. J Cell Sci 1998; 111 ( Pt 3):295-301. [PMID: 9427678 DOI: 10.1242/jcs.111.3.295] [Citation(s) in RCA: 59] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Microtubules provide the substrate for intracellular trafficking by association with molecular motors of the kinesin and dynein superfamilies. Motor proteins are generally thought to function as force generating units for transport of various cargoes along the microtubule polymer. Recent work suggests additional roles for motor proteins in changing the structure of the microtubule network itself. We report here that in the budding yeast Saccharomyces cerevisiae microtubule motors have antagonistic effects on microtubule numbers and lengths. As shown previously, loss of the Kar3p motor stimulates cytoplasmic microtubule growth while loss of Kip2p leads to a sharp reduction in cytoplasmic microtubule numbers. Loss of both the Kip2p and Kar3p motors together in the same cell produces an intermediate phenotype, suggesting that these two motors act in opposition to control cytoplasmic microtubule density. A Kip2p-GFP fusion from single gene expression is most concentrated at the spindle poles, as shown previously for an epitope tagged Kar3p-HA, suggesting both of these motors act from the minus ends of the microtubules to influence microtubule numbers.
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Affiliation(s)
- A Huyett
- Department of Biological Sciences, University of Pittsburgh, Pittsburgh, PA 15260, USA
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327
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Meluh PB, Koshland D. Budding yeast centromere composition and assembly as revealed by in vivo cross-linking. Genes Dev 1997; 11:3401-12. [PMID: 9407032 PMCID: PMC524546 DOI: 10.1101/gad.11.24.3401] [Citation(s) in RCA: 159] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The centromere-kinetochore complex is a specialized chromatin structure that mediates bipolar attachment of replicated chromosomes to the mitotic spindle, thereby ensuring proper sister chromatid separation during anaphase. The manner in which this important multimeric structure is specified and assembled within chromatin is unknown. Using in vivo cross-linking followed by immunoprecipitation, we show that the Mif2 protein of the budding yeast Saccharomyces cerevisiae, previously implicated in centromere function by genetic criteria, resides specifically at centromeric loci in vivo. This provides definitive evidence for structural conservation between yeast and mammalian centromeres, as Mif2p shares homology with CENP-C, a mammalian centromere protein. Ndc10p and Cbf1p, previously implicated in centromere function by genetic and in vitro biochemical assays, were also found to interact with centromeric DNA in vivo. By examining Mif2p, Ndc10p, and Cbf1p association with centromeric DNA derivatives, we demonstrate the existence of centromeric subcomplexes that may correspond to assembly intermediates. Based on these observations, we provide a simple model for centromere assembly. Finally, given the sensitivity of this technique, its application to other sequence-specific protein-DNA complexes within the cell, such as origins of replication and enhancer-promoter regions, could be of significant value.
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Affiliation(s)
- P B Meluh
- Howard Hughes Medical Institute, Carnegie Institution of Washington, Department of Embryology, Baltimore, Maryland 21210, USA.
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328
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Winey M, Yarar D, Giddings TH, Mastronarde DN. Nuclear pore complex number and distribution throughout the Saccharomyces cerevisiae cell cycle by three-dimensional reconstruction from electron micrographs of nuclear envelopes. Mol Biol Cell 1997; 8:2119-32. [PMID: 9362057 PMCID: PMC25696 DOI: 10.1091/mbc.8.11.2119] [Citation(s) in RCA: 183] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/1997] [Accepted: 08/12/1997] [Indexed: 02/05/2023] Open
Abstract
The number of nuclear pore complexes (NPCs) in individual nuclei of the yeast Saccharomyces cerevisiae was determined by computer-aided reconstruction of entire nuclei from electron micrographs of serially sectioned cells. Nuclei of 32 haploid cells at various points in the cell cycle were modeled and found to contain between 65 and 182 NPCs. Morphological markers, such as cell shape and nuclear shape, were used to determine the cell cycle stage of the cell being examined. NPC number was correlated with cell cycle stage to reveal that the number of NPCs increases steadily, beginning in G1-phase, suggesting that NPC assembly occurs continuously throughout the cell cycle. However, accumulation of nuclear envelope observed during the cell cycle, indicated by nuclear surface area, is not continuous at the same rate, such that the density of NPCs per unit area of nuclear envelope peaks in apparent S-phase cells. Analysis of the nuclear envelope reconstructions also revealed no preferred NPC-to-NPC distance. However, NPCs were found in large clusters over regions of the nuclear envelope. Interestingly, clusters of NPCs were most pronounced in early mitotic nuclei and were found to be associated with the spindle pole bodies, but the functional significance of this association is unknown.
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Affiliation(s)
- M Winey
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder 80309-0347, USA
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329
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Carminati JL, Stearns T. Microtubules orient the mitotic spindle in yeast through dynein-dependent interactions with the cell cortex. J Biophys Biochem Cytol 1997; 138:629-41. [PMID: 9245791 PMCID: PMC2141630 DOI: 10.1083/jcb.138.3.629] [Citation(s) in RCA: 409] [Impact Index Per Article: 15.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Proper orientation of the mitotic spindle is critical for successful cell division in budding yeast. To investigate the mechanism of spindle orientation, we used a green fluorescent protein (GFP)-tubulin fusion protein to observe microtubules in living yeast cells. GFP-tubulin is incorporated into microtubules, allowing visualization of both cytoplasmic and spindle microtubules, and does not interfere with normal microtubule function. Microtubules in yeast cells exhibit dynamic instability, although they grow and shrink more slowly than microtubules in animal cells. The dynamic properties of yeast microtubules are modulated during the cell cycle. The behavior of cytoplasmic microtubules revealed distinct interactions with the cell cortex that result in associated spindle movement and orientation. Dynein-mutant cells had defects in these cortical interactions, resulting in misoriented spindles. In addition, microtubule dynamics were altered in the absence of dynein. These results indicate that microtubules and dynein interact to produce dynamic cortical interactions, and that these interactions result in the force driving spindle orientation.
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Affiliation(s)
- J L Carminati
- Department of Biological Sciences, Stanford University, Stanford, California 94305-5020, USA
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330
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Straight AF, Marshall WF, Sedat JW, Murray AW. Mitosis in living budding yeast: anaphase A but no metaphase plate. Science 1997; 277:574-8. [PMID: 9228009 DOI: 10.1126/science.277.5325.574] [Citation(s) in RCA: 307] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Chromosome movements and spindle dynamics were visualized in living cells of the budding yeast Saccharomyces cerevisiae. Individual chromosomal loci were detected by expression of a protein fusion between green fluorescent protein (GFP) and the Lac repressor, which bound to an array of Lac operator binding sites integrated into the chromosome. Spindle microtubules were detected by expression of a protein fusion between GFP and Tub1, the major alpha tubulin. Spindle elongation and chromosome separation exhibited biphasic kinetics, and centromeres separated before telomeres. Budding yeast did not exhibit a conventional metaphase chromosome alignment but did show anaphase A, movement of the chromosomes to the poles.
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Affiliation(s)
- A F Straight
- Department of Physiology, Box 0444, School of Medicine, University of California at San Francisco, San Francisco, CA 94143-0444, USA
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331
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He X, Patterson TE, Sazer S. The Schizosaccharomyces pombe spindle checkpoint protein mad2p blocks anaphase and genetically interacts with the anaphase-promoting complex. Proc Natl Acad Sci U S A 1997; 94:7965-70. [PMID: 9223296 PMCID: PMC21538 DOI: 10.1073/pnas.94.15.7965] [Citation(s) in RCA: 216] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/20/1997] [Accepted: 05/16/1997] [Indexed: 02/04/2023] Open
Abstract
The spindle checkpoint monitors mitotic spindle integrity and the attachment of kinetochores to the spindle. Upon sensing a defect the checkpoint blocks cell cycle progression and thereby prevents chromosome missegregation. Previous studies in budding yeast show that the activated spindle checkpoint inhibits the onset of anaphase by an unknown mechanism. One possible target of the spindle checkpoint is anaphase promoting complex (APC), which controls all postmetaphase events that are blocked by spindle checkpoint activation. We have isolated mad2, a spindle checkpoint component in fission yeast, and shown that mad2 overexpression activates the checkpoint and causes a cell cycle arrest at the metaphase-to-anaphase transition. In addition to the observation that mad2-induced arrest can be partially relieved by mitosis-promoting factor inactivation, we present genetic evidence consistent with the hypothesis that the spindle checkpoint imposes a cell cycle arrest by inhibiting APC-dependent proteolysis.
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Affiliation(s)
- X He
- Verna and Marrs McLean Department of Biochemistry, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030, USA
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332
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Guacci V, Hogan E, Koshland D. Centromere position in budding yeast: evidence for anaphase A. Mol Biol Cell 1997; 8:957-72. [PMID: 9201708 PMCID: PMC305706 DOI: 10.1091/mbc.8.6.957] [Citation(s) in RCA: 89] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Although general features of chromosome movement during the cell cycle are conserved among all eukaryotic cells, particular aspects vary between organisms. Understanding the basis for these variations should provide significant insight into the mechanism of chromosome movement. In this context, establishing the types of chromosome movement in the budding yeast Saccharomyces cerevisiae is important since the complexes that mediate chromosome movement (microtubule organizing centers, spindles, and kinetochores) appear much simpler in this organism than in many other eukaryotic cells. We have used fluorescence in situ hybridization to begin an analysis of chromosome movement in budding yeast. Our results demonstrate that the position of yeast centromeres changes as a function of the cell cycle in a manner similar to other eukaryotes. Centromeres are skewed to the side of the nucleus containing the spindle pole in G1; away from the poles in mid-M and clustered near the poles in anaphase and telophase. The change in position of the centromeres relative to the spindle poles supports the existence of anaphase A in budding yeast. In addition, an anaphase A-like activity independent of anaphase B was demonstrated by following the change in centromere position in telophase-arrested cells upon depolymerization and subsequent repolymerization of microtubules. The roles of anaphase A activity and G1 centromere positioning in the segregation of budding yeast chromosomes are discussed. The fluorescence in situ hybridization methodology and experimental strategies described in this study provide powerful new tools to analyze mutants defective in specific kinesin-like molecules, spindle components, and centromere factors, thereby elucidating the mechanism of chromosome movement.
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Affiliation(s)
- V Guacci
- Department of Embryology, Carnegie Institution of Washington, Baltimore, Maryland 21210, USA
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333
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Affiliation(s)
- B Winsor
- Institut de Biologie Moléculaire et Cellulaire, UPR 9005 du CNRS, Strasbourg, France
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334
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Abstract
Cell duplication is characteristic of life. The coordination of cell growth with cell duplication and, specifically, the ordered steps necessary for this process are termed the cell cycle. Central to this process is the faithful replication and segregation of the chromosomes. The cycle consists of four phases: G1, where the decision to enter the cell cycle, which is known as Start, is made; S phase, during which the DNA is replicated; G2, during which controls assuring the completion of S phase operate; and M, or the mitotic phase, which is characterized by chromosome segregation, nuclear division, and cytokinesis. The budding yeast Saccharomyces cerevisiae has been developed into a model genetic system for the study of the cell division cycle (Hartwell et al. ["73] Genetics, 74:267-286). Here I review the basic processes by which chromosomes are segregated, with an emphasis on the physical structures fundamental to this process.
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Affiliation(s)
- S G Sobel
- Department of Cell Biology, Yale University, New Haven, Connecticut 06536-0812, USA
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335
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Abstract
In many cell types the formation of microtubules from tubulin subunits is initiated at defined nucleation sites at the centrosome. These sites contain the conserved gamma-tubulin which is in association with additional not very will characterised proteins, identified as components of a gamma-tubulin ring complex from Xenopus egg extracts or from suppressor screens in the yeast Saccharomyces cerevisiae. In this review we discuss two recently proposed models of how the gamma-tubulin complex assists in the assembly of tubulin to form microtubules. These models propose different roles for gamma-tubulin and the other proteins in the complex in tubulin assembly. While the structure and composition of a microtubule nucleation site is becoming clearer, it is still unknown how the cell-cycle dependent regulation of microtubule nucleation sites is achieved and whether they disassemble after microtubule formation in order to allow microtubule fluxes towards the centrosome which have been observed in mitotic cells.
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Affiliation(s)
- G Pereira
- Max-Planck Institut für Biochemie, Genzentrum, Martinsried, Germany
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336
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Abstract
Activation of a facultative, dicentric chromosome provides a unique opportunity to introduce a double strand DNA break into a chromosome at mitosis. Time lapse video enhanced-differential interference contrast analysis of the cellular response upon dicentric activation reveals that the majority of cells initiates anaphase B, characterized by pole-pole separation, and pauses in mid-anaphase for 30-120 min with spindles spanning the neck of the bud before completing spindle elongation and cytokinesis. The length of the spindle at the delay point (3-4 microm) is not dependent on the physical distance between the two centromeres, indicating that the arrest represents surveillance of a dicentric induced aberration. No mid-anaphase delay is observed in the absence of the RAD9 checkpoint gene, which prevents cell cycle progression in the presence of damaged DNA. These observations reveal RAD9-dependent events well past the G2/M boundary and have considerable implications in understanding how chromosome integrity and the position and state of the mitotic spindle are monitored before cytokinesis.
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Affiliation(s)
- S S Yang
- Department of Biology, University of North Carolina, Chapel Hill 27599-3280, USA
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337
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O'Toole ET, Mastronarde DN, Giddings TH, Winey M, Burke DJ, McIntosh JR. Three-dimensional analysis and ultrastructural design of mitotic spindles from the cdc20 mutant of Saccharomyces cerevisiae. Mol Biol Cell 1997; 8:1-11. [PMID: 9017591 PMCID: PMC276055 DOI: 10.1091/mbc.8.1.1] [Citation(s) in RCA: 47] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The three-dimensional organization of mitotic microtubules in a mutant strain of Saccharomyces cerevisiae has been studied by computer-assisted serial reconstruction. At the nonpermissive temperature, cdc20 cells arrested with a spindle length of approximately 2.5 microns. These spindles contained a mean of 81 microtubules (range, 56-100) compared with 23 in wild-type spindles of comparable length. This increase in spindle microtubule number resulted in a total polymer length up to four times that of wild-type spindles. The spindle pole bodies in the cdc20 cells were approximately 2.3 times the size of wild-type, thereby accommodating the abnormally large number of spindle microtubules. The cdc20 spindles contained a large number of interpolar microtubules organized in a "core bundle." A neighbor density analysis of this bundle at the spindle midzone showed a preferred spacing of approximately 35 nm center-to-center between microtubules of opposite polarity. Although this is evidence of specific interaction between antiparallel microtubules, mutant spindles were less ordered than the spindle of wild-type cells. The number of noncore microtubules was significantly higher than that reported for wild-type, and these microtubules did not display a characteristic metaphase configuration. cdc20 spindles showed significantly more cross-bridges between spindle microtubules than were seen in the wild type. The cross-bridge density was highest between antiparallel microtubules. These data suggest that spindle microtubules are stabilized in cdc20 cells and that the CDC20 gene product may be involved in cell cycle processes that promote spindle microtubule disassembly.
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Affiliation(s)
- E T O'Toole
- Boulder Laboratory for 3-D Fine Structure, Department of Molecular, Cellular, and Developmental Biology, University of Colorado 80309-0347, USA
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338
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Abstract
Much of our understanding of the molecular basis of mitotic spindle function has been achieved within the past decade. Studies utilizing genetically tractable organisms have made important contributions to this field and these studies form the basis of this review. We focus upon three areas of spindle research: spindle poles, centromeres, and spindle motors. The structure and duplication mechanisms of spindle poles are considered as well as their roles in organizing spindle microtubules. Centromeres vary considerably in their size and complexity. We describe recent progress in our understanding of the relatively simple centromeres of the yeast Saccharomyces cerevisiae and the complex centromeres that are more typical of eukaryotic cells. Microtubule-based motor proteins that generate the characteristic spindle movements have been identified in recent years and can be grouped into families defined by conserved primary sequence and mitotic function.
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Affiliation(s)
- M A Hoyt
- Department of Biology, Johns Hopkins University, Baltimore, Maryland 21218, USA
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339
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Kilmartin JV, Goh PY. Spc110p: assembly properties and role in the connection of nuclear microtubules to the yeast spindle pole body. EMBO J 1996; 15:4592-602. [PMID: 8887551 PMCID: PMC452189] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Spc110p is an essential component of the budding yeast spindle pole body (SPB). It binds calmodulin and contains a long central coiled-coil rod which acts as a spacer element between the central plaque of the SPB and the ends of the nuclear or spindle microtubules. This suggests that the essential function of Spc110p is to connect the nuclear microtubules to the SPB. To confirm this, we examined the phenotype of ts alleles of SPC110, one of which contains a mutation in the calmodulin binding site and was suppressed by overexpression of calmodulin. The alleles fail to form a functional mitotic spindle because spindle microtubules are not properly connected to the SPB. We also examined the phenotype of the toxic overexpression of either the wild-type or a truncated version of Spc110p containing a deletion of most of the coiled-coil domain. Both of these proteins form large ordered spheroidal polymers in the nucleus. The polymerization of the truncated Spc110p appears to be initiated inside the SPB from the position where Spc110p is normally located, and as the polymer grows in size it severs the connection between the nuclear microtubules and the SPB. The polymers were purified and are composed of Spc110p and calmodulin. A model for the structure of the polymer is proposed.
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340
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Hardwick KG, Weiss E, Luca FC, Winey M, Murray AW. Activation of the budding yeast spindle assembly checkpoint without mitotic spindle disruption. Science 1996; 273:953-6. [PMID: 8688079 DOI: 10.1126/science.273.5277.953] [Citation(s) in RCA: 267] [Impact Index Per Article: 9.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
The spindle assembly checkpoint keeps cells with defective spindles from initiating chromosome segregation. The protein kinase Mps1 phosphorylates the yeast protein Mad1p when this checkpoint is activated, and the overexpression of Mps1p induces modification of Mad1p and arrests wild-type yeast cells in mitosis with morphologically normal spindles. Spindle assembly checkpoint mutants overexpressing Mps1p pass through mitosis without delay and can produce viable progeny, which demonstrates that the arrest of wild-type cells results from inappropriate activation of the checkpoint in cells whose spindle is fully functional. Ectopic activation of cell-cycle checkpoints might be used to exploit the differences in checkpoint status between normal and tumor cells and thus improve the selectivity of chemotherapy.
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Affiliation(s)
- K G Hardwick
- Department of Physiology, University of California, San Francisco, CA 94143-0444, USA
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341
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Chibana H, Tanaka K. Analysis of the cell cycle in the budding yeast Candida albicans by positioning of chromosomes by fluorescence in situ hybridization (FISH) with repetitive sequences. Genes Cells 1996; 1:727-40. [PMID: 9077442 DOI: 10.1111/j.1365-2443.1996.tb00013.x] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
BACKGROUND In the budding yeasts, including Saccharomyces cerevisiae, in which individual chromosomes cannot be visualized by microscopy, the mitotic phases in the cell cycle have not been correlated with the chromosome behaviour. We used various repetitive sequences, namely, rDNA, telomeric sequences and RPSs, which are localized in limited regions in almost all chromosomes, as probes for fluorescence in situ hybridization (FISH) to analyse the cell cycle phases in a pathogenic yeast Candida albicans. The positioning of the FISH signals was analysed quantitatively in relation to the length of spindle microtubules in the nuclear domain. RESULTS RPSs were randomly distributed in the interphase nucleus, and they formed aggregates with the development of the spindle. DNA synthesis was complete before RPSs came closest to the spindle. As the spindle elongated, they were scattered along the spindle and then separated into two clusters at the spindle poles at the end of anaphase. rDNA was localized in the nucleolar domain, and telomere signals were randomly distributed throughout mitosis. CONCLUSION By estimating quantitatively the proportions of mitotic cells with particular configurations of both microtubules and chromosomes in a population of rapidly proliferating cells, we were able to define various stages in the progression of mitosis. The S phase and pro-to-prometaphase were overlapping and the G2 phase was lacking. Unexpectedly, the pole-to-pole elongation of the spindle (anaphase B) was predominating and was followed by movement of chromosomes to the poles (anaphase A).
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Affiliation(s)
- H Chibana
- Laboratory of Medical Mycology, Nagoya University School of Medicine, Showa-ku, Japan
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342
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McDonald K, O'Toole ET, Mastronarde DN, Winey M, Richard McIntosh J. Mapping the three-dimensional organization of microtubules in mitotic spindles of yeast. Trends Cell Biol 1996; 6:235-9. [PMID: 15157462 DOI: 10.1016/0962-8924(96)40003-4] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Affiliation(s)
- K McDonald
- Electron Microscope Laboratory, 26 Giannini Hall, University of California, Berkeley, CA 94720-3330, USA
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343
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Aitchison JD, Blobel G, Rout MP. Nup120p: a yeast nucleoporin required for NPC distribution and mRNA transport. J Cell Biol 1995; 131:1659-75. [PMID: 8557736 PMCID: PMC2120676 DOI: 10.1083/jcb.131.6.1659] [Citation(s) in RCA: 129] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
To extend our understanding of the mechanism by which the nuclear pore complex (NPC) mediates macromolecular transport across the nuclear envelope we have focused on defining the composition and molecular organization of the yeast NPC. Peptide sequence analysis of a polypeptide with a M(r) of approximately 100,000 present in a highly enriched yeast NPC fraction identified a novel yeast nucleoporin we term Nup120p. Nup120p corresponds to the open reading frame (ORF) YKL057c identified by the yeast genome sequencing project. The ORF predicts a protein with a calculated molecular mass of 120.5 kD containing two leucine zipper motifs, a short coiled-coil region and limited primary sequence similarity to Nup133p. Nup120p was localized to the NPC using a protein A-tagged chimera in situ by indirect immunofluorescence microscopy. Deletion of the NUP120 gene caused clustering of NPCs at one side of the nuclear envelope, moderate nucleolar fragmentation and slower cell growth. Transfer of nup120 delta cells to 37 degrees C resulted in the nuclear accumulation of poly(A)+ mRNA, extensive fragmentation of the nucleolus, spindle defects, and cell death.
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Affiliation(s)
- J D Aitchison
- Laboratory of Cell Biology, Howard Hughes Medical Institute, Rockefeller University, New York 10021-6399, USA
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344
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Pellman D, Bagget M, Tu YH, Fink GR, Tu H. Two microtubule-associated proteins required for anaphase spindle movement in Saccharomyces cerevisiae. J Cell Biol 1995; 130:1373-85. [PMID: 7559759 PMCID: PMC2120566 DOI: 10.1083/jcb.130.6.1373] [Citation(s) in RCA: 131] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
In many eucaryotic cells, the midzone of the mitotic spindle forms a distinct structure containing a specific set of proteins. We have isolated ASE1, a gene encoding a component of the Saccharomyces cerevisiae spindle midzone. Strains lacking both ASE1 and BIK1, which encodes an S. cerevisiae microtubule-associated protein, are inviable. The analysis of the phenotype of a bik1 ase1 conditional double mutant suggests that BIK1 and ASE1 are not required for the assembly of a bipolar spindle, but are essential for anaphase spindle elongation. The steady-state levels of Ase1p are regulated in a manner that is consistent with a function during anaphase: they are low in G1, accumulate to maximal levels after S phase and then drop as cells exit mitosis. Components of the spindle midzone may therefore be required in vivo for anaphase spindle movement. Additionally, anaphase spindle movement may depend on a dedicated set of genes whose expression is induced at G2/M.
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Affiliation(s)
- D Pellman
- Whitehead Institute for Biomedical Research, Cambridge, Massachusetts 02142, USA
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