51
|
Lavoie BD, Hogan E, Koshland D. In vivo dissection of the chromosome condensation machinery: reversibility of condensation distinguishes contributions of condensin and cohesin. J Cell Biol 2002; 156:805-15. [PMID: 11864994 PMCID: PMC2173308 DOI: 10.1083/jcb.200109056] [Citation(s) in RCA: 143] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/18/2001] [Revised: 01/18/2002] [Accepted: 01/20/2002] [Indexed: 12/30/2022] Open
Abstract
The machinery mediating chromosome condensation is poorly understood. To begin to dissect the in vivo function(s) of individual components, we monitored mitotic chromosome structure in mutants of condensin, cohesin, histone H3, and topoisomerase II (topo II). In budding yeast, both condensation establishment and maintenance require all of the condensin subunits, but not topo II activity or phospho-histone H3. Structural maintenance of chromosome (SMC) protein 2, as well as each of the three non-SMC proteins (Ycg1p, Ycs4p, and Brn1p), was required for chromatin binding of the condensin complex in vivo. Using reversible condensin alleles, we show that chromosome condensation does not involve an irreversible modification of condensin or chromosomes. Finally, we provide the first evidence of a mechanistic link between condensin and cohesin function. A model discussing the functional interplay between cohesin and condensin is presented.
Collapse
Affiliation(s)
- Brigitte D Lavoie
- Department of Medical Genetics and Microbiology, University of Toronto, Toronto, ON M5S 1A8, Canada.
| | | | | |
Collapse
|
52
|
Bhalla N, Biggins S, Murray AW. Mutation of YCS4, a budding yeast condensin subunit, affects mitotic and nonmitotic chromosome behavior. Mol Biol Cell 2002; 13:632-45. [PMID: 11854418 PMCID: PMC65655 DOI: 10.1091/mbc.01-05-0264] [Citation(s) in RCA: 147] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
The budding yeast YCS4 gene encodes a conserved regulatory subunit of the condensin complex. We isolated an allele of this gene in a screen for mutants defective in sister chromatid separation or segregation. The phenotype of the ycs4-1 mutant is similar to topoisomerase II mutants and distinct from the esp1-1 mutant: the topological resolution of sister chromatids is compromised in ycs4-1 despite normal removal of cohesins from mitotic chromosomes. Consistent with a role in sister separation, YCS4 function is required to localize DNA topoisomerase I and II to chromosomes. Unlike its homologs in Xenopus and fission yeast, Ycs4p is associated with chromatin throughout the cell cycle; the only change in localization occurs during anaphase when the protein is enriched at the nucleolus. This relocalization may reveal the specific challenge that segregation of the transcriptionally hyperactive, repetitive array of rDNA genes can present during mitosis. Indeed, segregation of the nucleolus is abnormal in ycs4-1 at the nonpermissive temperature. Interrepeat recombination in the rDNA array is specifically elevated in ycs4-1 at the permissive temperature, suggesting that the Ycs4p plays a role at the array aside from its segregation. Furthermore, ycs4-1 is defective in silencing at the mating type loci at the permissive temperature. Taken together, our data suggest that there are mitotic as well as nonmitotic chromosomal abnormalities associated with loss of condensin function in budding yeast.
Collapse
Affiliation(s)
- Needhi Bhalla
- Department of Cell Biology and Physiology, University of California, San Francisco, San Francisco, California 94143, USA
| | | | | |
Collapse
|
53
|
Ouspenski II, Cabello OA, Brinkley BR. Chromosome condensation factor Brn1p is required for chromatid separation in mitosis. Mol Biol Cell 2000; 11:1305-13. [PMID: 10749931 PMCID: PMC14848 DOI: 10.1091/mbc.11.4.1305] [Citation(s) in RCA: 86] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
This work describes BRN1, the budding yeast homologue of Drosophila Barren and Xenopus condensin subunit XCAP-H. The Drosophila protein is required for proper chromosome segregation in mitosis, and Xenopus protein functions in mitotic chromosome condensation. Mutant brn1 cells show a defect in mitotic chromosome condensation and sister chromatid separation and segregation in anaphase. Chromatid cohesion before anaphase is properly maintained in the mutants. Some brn1 mutant cells apparently arrest in S-phase, pointing to a possible function for Brn1p at this stage of the cell cycle. Brn1p is a nuclear protein with a nonuniform distribution pattern, and its level is up-regulated at mitosis. Temperature-sensitive mutations of BRN1 can be suppressed by overexpression of a novel gene YCG1, which is homologous to another Xenopus condensin subunit, XCAP-G. Overexpression of SMC2, a gene necessary for chromosome condensation, and a homologue of the XCAP-E condensin, does not suppress brn1, pointing to functional specialization of components of the condensin complex.
Collapse
Affiliation(s)
- I I Ouspenski
- Department of Molecular Biology, Baylor College of Medicine, Houston, Texas 77030, USA
| | | | | |
Collapse
|
54
|
Lavoie BD, Tuffo KM, Oh S, Koshland D, Holm C. Mitotic chromosome condensation requires Brn1p, the yeast homologue of Barren. Mol Biol Cell 2000; 11:1293-304. [PMID: 10749930 PMCID: PMC14847 DOI: 10.1091/mbc.11.4.1293] [Citation(s) in RCA: 113] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
In vitro studies suggest that the Barren protein may function as an activator of DNA topoisomerase II and/or as a component of the Xenopus condensin complex. To better understand the role of Barren in vivo, we generated conditional alleles of the structural gene for Barren (BRN1) in Saccharomyces cerevisiae. We show that Barren is an essential protein required for chromosome condensation in vivo and that it is likely to function as an intrinsic component of the yeast condensation machinery. Consistent with this view, we show that Barren performs an essential function during a period of the cell cycle when chromosome condensation is established and maintained. In contrast, Barren does not serve as an essential activator of DNA topoisomerase II in vivo. Finally, brn1 mutants display additional phenotypes such as stretched chromosomes, aberrant anaphase spindles, and the accumulation of cells with >2C DNA content, suggesting that Barren function influences multiple aspects of chromosome transmission and dynamics.
Collapse
Affiliation(s)
- B D Lavoie
- Department of Embryology, Howard Hughes Medical Institute, Carnegie Institution of Washington, Baltimore, Maryland 21210, USA.
| | | | | | | | | |
Collapse
|
55
|
Chen C, Merrill BJ, Lau PJ, Holm C, Kolodner RD. Saccharomyces cerevisiae pol30 (proliferating cell nuclear antigen) mutations impair replication fidelity and mismatch repair. Mol Cell Biol 1999; 19:7801-15. [PMID: 10523669 PMCID: PMC84846 DOI: 10.1128/mcb.19.11.7801] [Citation(s) in RCA: 87] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
To understand the role of POL30 in mutation suppression, 11 Saccharomyces cerevisiae pol30 mutator mutants were characterized. These mutants were grouped based on their mutagenic defects. Many pol30 mutants harbor multiple mutagenic defects and were placed in more than one group. Group A mutations (pol30-52, -104, -108, and -126) caused defects in mismatch repair (MMR). These mutants exhibited mutation rates and spectra reminiscent of MMR-defective mutants and were defective in an in vivo MMR assay. The mutation rates of group A mutants were enhanced by a msh2 or a msh6 mutation, indicating that MMR deficiency is not the only mutagenic defect present. Group B mutants (pol30-45, -103, -105, -126, and -114) exhibited increased accumulation of either deletions alone or a combination of deletions and duplications (4 to 60 bp). All deletion and duplication breakpoints were flanked by 3 to 7 bp of imperfect direct repeats. Genetic analysis of one representative group B mutant, pol30-126, suggested polymerase slippage as the likely mutagenic mechanism. Group C mutants (pol30-100, -103, -105, -108, and -114) accumulated base substitutions and exhibited synergistic increases in mutation rate when combined with msh6 mutations, suggesting increased DNA polymerase misincorporation as a mutagenic defect. The synthetic lethality between a group A mutant, pol30-104, and rad52 was almost completely suppressed by the inactivation of MSH2. Moreover, pol30-104 caused a hyperrecombination phenotype that was partially suppressed by a msh2 mutation. These results suggest that pol30-104 strains accumulate DNA breaks in a MSH2-dependent manner.
Collapse
Affiliation(s)
- C Chen
- Ludwig Institute for Cancer Research, University of California-San Diego School of Medicine, La Jolla, California 92093, USA
| | | | | | | | | |
Collapse
|
56
|
Verkade HM, Bugg SJ, Lindsay HD, Carr AM, O'Connell MJ. Rad18 is required for DNA repair and checkpoint responses in fission yeast. Mol Biol Cell 1999; 10:2905-18. [PMID: 10473635 PMCID: PMC25529 DOI: 10.1091/mbc.10.9.2905] [Citation(s) in RCA: 121] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
To survive damage to the genome, cells must respond by activating both DNA repair and checkpoint responses. Using genetic screens in the fission yeast Schizosaccharomyces pombe, we recently isolated new genes required for DNA damage checkpoint control. We show here that one of these strains defines a new allele of the previously described rad18 gene, rad18-74. rad18 is an essential gene, even in the absence of extrinsic DNA damage. It encodes a conserved protein related to the structural maintenance of chromosomes proteins. Point mutations in rad18 lead to defective DNA repair pathways responding to both UV-induced lesions and, as we show here, double-stranded breaks. Furthermore, rad18p is required to maintain cell cycle arrest in the presence of DNA damage, and failure of this leads to highly aberrant mitoses. A gene encoding a BRCT-containing protein, brc1, was isolated as an allele-specific high-copy suppressor of rad18-74. brc1 is required for mitotic fidelity and for cellular viability in strains with rad18 mutations but is not essential for DNA damage responses. Mutations in rad18 and brc1 are synthetically lethal with a topoisomerase II mutant (top2-191), indicating that these proteins play a role in chromatin organization. These studies show a role for chromatin organization in the maintenance or activation of responses to DNA damage.
Collapse
Affiliation(s)
- H M Verkade
- Trescowthick Research Laboratories, Peter MacCallum Cancer Institute, Melbourne, Victoria 8006, Australia
| | | | | | | | | |
Collapse
|
57
|
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.
Collapse
Affiliation(s)
- J H Kim
- Department of Microbiology and Institute for Cellular and Molecular Biology, The University of Texas, Austin, Texas 78712, USA
| | | | | |
Collapse
|
58
|
Pâques F, Haber JE. Multiple pathways of recombination induced by double-strand breaks in Saccharomyces cerevisiae. Microbiol Mol Biol Rev 1999; 63:349-404. [PMID: 10357855 PMCID: PMC98970 DOI: 10.1128/mmbr.63.2.349-404.1999] [Citation(s) in RCA: 1649] [Impact Index Per Article: 66.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The budding yeast Saccharomyces cerevisiae has been the principal organism used in experiments to examine genetic recombination in eukaryotes. Studies over the past decade have shown that meiotic recombination and probably most mitotic recombination arise from the repair of double-strand breaks (DSBs). There are multiple pathways by which such DSBs can be repaired, including several homologous recombination pathways and still other nonhomologous mechanisms. Our understanding has also been greatly enriched by the characterization of many proteins involved in recombination and by insights that link aspects of DNA repair to chromosome replication. New molecular models of DSB-induced gene conversion are presented. This review encompasses these different aspects of DSB-induced recombination in Saccharomyces and attempts to relate genetic, molecular biological, and biochemical studies of the processes of DNA repair and recombination.
Collapse
Affiliation(s)
- F Pâques
- Rosenstiel Center and Department of Biology, Brandeis University, Waltham, Massachusetts 02454-9110, USA
| | | |
Collapse
|
59
|
Gangloff S, de Massy B, Arthur L, Rothstein R, Fabre F. The essential role of yeast topoisomerase III in meiosis depends on recombination. EMBO J 1999; 18:1701-11. [PMID: 10075939 PMCID: PMC1171256 DOI: 10.1093/emboj/18.6.1701] [Citation(s) in RCA: 107] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
Yeast cells mutant for TOP3, the gene encoding the evolutionary conserved type I-5' topoisomerase, display a wide range of phenotypes including altered cell cycle, hyper-recombination, abnormal gene expression, poor mating, chromosome instability and absence of sporulation. In this report, an analysis of the role of TOP3 in the meiotic process indicates that top3Delta mutants enter meiosis and complete the initial steps of recombination. However, reductional division does not occur. Deletion of the SPO11 gene, which prevents recombination between homologous chromosomes in meiosis I division, allows top3Delta mutants to form viable spores, indicating that Top3 is required to complete recombination successfully. A topoisomerase activity is involved in this process, since expression of bacterial TopA in yeast top3Delta mutants permits sporulation. The meiotic block is also partially suppressed by a deletion of SGS1, a gene encoding a helicase that interacts with Top3. We propose an essential role for Top3 in the processing of molecules generated during meiotic recombination.
Collapse
Affiliation(s)
- S Gangloff
- CEA de Fontenay-aux-roses, UMR 217 CNRS-CEA, BP 6, 92265 Fontenay-aux-roses.
| | | | | | | | | |
Collapse
|
60
|
Hartsuiker E, Bähler J, Kohli J. The role of topoisomerase II in meiotic chromosome condensation and segregation in Schizosaccharomyces pombe. Mol Biol Cell 1998; 9:2739-50. [PMID: 9763441 PMCID: PMC25549 DOI: 10.1091/mbc.9.10.2739] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Topoisomerase II is able to break and rejoin double-strand DNA. It controls the topological state and forms and resolves knots and catenanes. Not much is known about the relation between the chromosome segregation and condensation defects as found in yeast top2 mutants and the role of topoisomerase II in meiosis. We studied meiosis in a heat-sensitive top2 mutant of Schizosaccharomyces pombe. Topoisomerase II is not required until shortly before meiosis I. The enzyme is necessary for condensation shortly before the first meiotic division but not for early meiotic prophase condensation. DNA replication, prophase morphology, and dynamics of the linear elements are normal in the top2 mutant. The top2 cells are not able to perform meiosis I. Arrested cells have four spindle pole bodies and two spindles but only one nucleus, suggesting that the arrest is nonregulatory. Finally, we show that the arrest is partly solved in a top2 rec7 double mutant, indicating that topoisomerase II functions in the segregation of recombined chromosomes. We suggest that the inability to decatenate the replicated DNA is the primary defect in top2. This leads to a loss of chromatin condensation shortly before meiosis I, failure of sister chromatid separation, and a nonregulatory arrest.
Collapse
Affiliation(s)
- E Hartsuiker
- Institute of General Microbiology, University of Bern, 3012 Bern, Switzerland.
| | | | | |
Collapse
|
61
|
Borde V, Duguet M. DNA topoisomerase II sites in the histone H4 gene during the highly synchronous cell cycle of Physarum polycephalum. Nucleic Acids Res 1998; 26:2042-49. [PMID: 9547257 PMCID: PMC147523 DOI: 10.1093/nar/26.9.2042] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The nearly perfect synchrony of nuclear division in a plasmodium of Physarum polycephalum provides a powerful system to analyze topoisomerase II cleavage sites in the course of the cell cycle. The histone H4 locus, whose schedule of replication and transcription is precisely known, was chosen for this analysis. Drug-induced topoisomerase II sites are clustered downstream of the histone H4 gene and appear highly dependent on cell cycle stage. They were only detected in mitosis and at the very beginning of S phase, precisely at the time of replication of the histone H4 region. The sites, which were absent in G2 phase, reappeared at the next mitosis. Remarkably, DNase I hypersensitive sites occurred in nearly the same location, but their schedule was totally different: they were absent in mitosis and present in G2. This schedule follows H4 transcription, which peaks in mid-S phase and in the second part of G2 phase and is off during mitosis. These results suggest that topoisomerase II may not be involved in transcription, but plays a role in remodeling chromatin structure, both during chromosome condensation in prophase/metaphase to allow their decatenation and during chromosome decondensation after metaphase to allow replication fork passage throughout the region.
Collapse
Affiliation(s)
- V Borde
- Laboratoire d'Enzymologie des Acides Nucléiques, Institut de Génétique et Microbiologie, URA 2225 CNRS, Bât. 400, Université de Paris Sud, Centre d'Orsay, 91405 Orsay Cedex, France
| | | |
Collapse
|
62
|
Fiorentino DF, Crabtree GR. Characterization of Saccharomyces cerevisiae dna2 mutants suggests a role for the helicase late in S phase. Mol Biol Cell 1997; 8:2519-37. [PMID: 9398673 PMCID: PMC25725 DOI: 10.1091/mbc.8.12.2519] [Citation(s) in RCA: 50] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/1996] [Accepted: 09/29/1997] [Indexed: 02/05/2023] Open
Abstract
The TOR proteins, originally identified as targets of the immunosuppressant rapamycin, contain an ATM-like "lipid kinase" domain and are required for early G1 progression in eukaryotes. Using a screen to identify Saccharomyces cerevisiae mutants requiring overexpression of Tor1p for viability, we have isolated mutations in a gene we call ROT1 (requires overexpression of Tor1p). This gene is identical to DNA2, encoding a helicase required for DNA replication. As with its role in cell cycle progression, both the N-terminal and C-terminal regions, as well as the kinase domain of Tor1p, are required for rescue of dna2 mutants. Dna2 mutants are also rescued by Tor2p and show synthetic lethality with tor1 deletion mutants under specific conditions. Temperature-sensitive (Ts) dna2 mutants arrest irreversibly at G2/M in a RAD9- and MEC1-dependent manner, suggesting that Dna2p has a role in S phase. Frequencies of mitotic recombination and chromosome loss are elevated in dna2 mutants, also supporting a role for the protein in DNA synthesis. Temperature-shift experiments indicate that Dna2p functions during late S phase, although dna2 mutants are not deficient in bulk DNA synthesis. These data suggest that Dna2p is not required for replication fork progression but may be needed for a later event such as Okazaki fragment maturation.
Collapse
MESH Headings
- Adenosine Triphosphatases/chemistry
- Adenosine Triphosphatases/genetics
- Adenosine Triphosphatases/metabolism
- Amino Acid Sequence
- Cell Cycle Proteins/genetics
- Cell Cycle Proteins/metabolism
- Cloning, Molecular
- DNA Helicases/chemistry
- DNA Helicases/genetics
- DNA Helicases/metabolism
- DNA Replication/genetics
- DNA, Fungal/biosynthesis
- DNA, Fungal/chemistry
- DNA, Fungal/genetics
- DNA, Fungal/metabolism
- Fungal Proteins/chemistry
- Fungal Proteins/genetics
- Fungal Proteins/metabolism
- Gene Expression
- Genes, Essential/genetics
- Genes, Fungal/genetics
- Genes, Fungal/physiology
- Genes, Suppressor/genetics
- Intracellular Signaling Peptides and Proteins
- Molecular Sequence Data
- Mutation/genetics
- Phenotype
- Phosphatidylinositol 3-Kinases
- Phosphotransferases (Alcohol Group Acceptor)/chemistry
- Phosphotransferases (Alcohol Group Acceptor)/genetics
- Phosphotransferases (Alcohol Group Acceptor)/metabolism
- Protein Binding
- Protein Serine-Threonine Kinases
- Recombination, Genetic/genetics
- S Phase/genetics
- Saccharomyces cerevisiae/cytology
- Saccharomyces cerevisiae/enzymology
- Saccharomyces cerevisiae/genetics
- Saccharomyces cerevisiae Proteins
- Sequence Deletion/genetics
- Temperature
Collapse
Affiliation(s)
- D F Fiorentino
- Department of Developmental Biology, Howard Hughes Medical Institute, Stanford University School of Medicine, Stanford, California 94305, USA
| | | |
Collapse
|
63
|
Holden JA, Rahn MP, Jolles CJ, Vorobyev SV, Bronstein IB. Immunohistochemical detection of DNA topoisomerase I in formalin fixed, paraffin wax embedded normal tissues and in ovarian carcinomas. Mol Pathol 1997; 50:247-53. [PMID: 9497914 PMCID: PMC379640 DOI: 10.1136/mp.50.5.247] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
AIMS To determine, by in situ immunohistochemistry, whether ovarian carcinomas have increased expression of DNA topoisomerase I. METHODS Paraffin wax blocks obtained from 15 samples of normal human tissues and from 14 cases of ovarian cancer were cut on to glass slides and immunohistochemically stained for topoisomerase I. The primary antibody was a mouse monoclonal that recognises topoisomerase I in western blots. Colour was detected using a peroxidase system with diaminobenzidine as the chromogen. The expression of topoisomerase I in the tissues and tumours was graded subjectively from 0 to 3+ based on the colour intensity of the immunostain. RESULTS In normal tissues, topoisomerase I expression was strongest in the mucosal lymphocytes in the gastrointestinal tract and in the germinal centres of the tonsil. Weak topoisomerase I staining was found in the columnar epithelium of the gastrointestinal tract and in squamous mucosa. In the series of ovarian carcinomas, raised topoisomerase I was observed in 43% (6 of 14) of the tumours. Of the tumours with raised topoisomerase I, only three contained a population of rapidly cycling cells. Therefore, 21% of our series of ovarian carcinomas (3 of 14) had raised topoisomerase I expression and were proliferating rapidly. CONCLUSIONS Topoisomerase I expression in formalin fixed, paraffin wax embedded human tissues can be evaluated by immunohistochemical staining. Increases in topoisomerase I occur in some cases of ovarian cancer.
Collapse
Affiliation(s)
- J A Holden
- Department of Pathology, University of Utah Health Sciences Center, Salt Lake City 84132, USA
| | | | | | | | | |
Collapse
|
64
|
Keller BA, Patel S, Fisher LM. Molecular cloning and expression of the Candida albicans TOP2 gene allows study of fungal DNA topoisomerase II inhibitors in yeast. Biochem J 1997; 324 ( Pt 1):329-39. [PMID: 9164874 PMCID: PMC1218434 DOI: 10.1042/bj3240329] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
Candida albicans topoisomerase II, encoded by the TOP2 gene, mediates chromosome segregation by a double-strand DNA break mechanism and is a potential target for anti-fungal therapy. In this paper, we report the characterization of the C. albicans TOP2 gene and its use to develop a yeast system that allows the identification and study of anti-fungal topoisomerase II inhibitors in vivo. The gene, specifying a 1461-residue polypeptide with only 40% identity with human topoisomerase IIalpha and beta isoforms, was isolated from C. albicans on a 6.3 kb EcoRI fragment that mapped to chromosome 4. It was used to construct a plasmid in which TOP2 expresses a recombinant enzyme (residues 57-1461 of C. albicans topoisomerase II fused to the first five residues of Saccharomyces cerevisiae topoisomerase II) under the control of a galactose-inducible promoter. The plasmid rescued the lethal phenotype of a temperature-sensitive S. cerevisiae DNA topoisomerase II mutant allowing growth at 35 degrees C. Yeast cells, bearing ISE2 permeability and rad52 double-strand-break-repair mutations the growth of which at 35 degrees C was dependent on C. albicans topoisomerase II, were killed by the known topoisomerase II inhibitors amsacrine and doxorubicin. Parallel experiments in yeast expressing human topoisomerase IIalpha allowed the relative sensitivities of the fungal and host topoisomerases to be examined in the same genetic background. To compare the killing in vivo with drug inhibition in vitro, the recombinant C. albicans topoisomerase II protein was expressed and purified to near-homogeneity from S. cerevisiae yielding a 160 kDa polypeptide that displayed the expected ATP-dependent DNA-relaxation and DNA-decatenation activities. The enzyme, whether examined in vitro or complementing in S. cerevisiae, was comparably sensitive to amsacrine and doxorubicin. Our results suggest that potential topoisomerase II-targeting anti-fungal inhibitors can be identified and studied in S. cerevisiae.
Collapse
Affiliation(s)
- B A Keller
- Molecular Genetics Group, Department of Cellular and Molecular Sciences, St. George's Hospital Medical School, University of London, Cranmer Terrace, London SW17 0RE, U.K
| | | | | |
Collapse
|
65
|
Wang X, Watt PM, Louis EJ, Borts RH, Hickson ID. Pat1: a topoisomerase II-associated protein required for faithful chromosome transmission in Saccharomyces cerevisiae. Nucleic Acids Res 1996; 24:4791-7. [PMID: 8972867 PMCID: PMC146302 DOI: 10.1093/nar/24.23.4791] [Citation(s) in RCA: 52] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Saccharomyces cerevisiae top2 mutants deficient in topoisomerase II activity are defective in chromosome segregation during both mitotic and meiotic cell divisions. To identify proteins that act in concert with topoisomerase II during chromosome segregation in S.cerevisiae, we have used a two-hybrid cloning approach. We report the isolation of the PAT1 gene (for protein associated with topoisomerase II), which encodes a novel 90 kDa proline- and glutamine-rich protein that interacts with a highly conserved, leucine-rich region of topoisomerase II in vivo. Strains lacking Pat1p exhibit a slow growth rate and a phenotype reminiscent of conditional top2 mutants grown at the semi-permissive temperature; most notably, a reduced fidelity of chromosome segregation during both mitosis and meiosis. These findings indicate that the PAT1 gene is necessary for accurate chromosome transmission during cell division in eukaryotic cells and suggest that the interaction of Pat1p and topoisomerase II is an important component of this function.
Collapse
Affiliation(s)
- X Wang
- Institute of Molecular Medicine, John Radcliffe Hospital, Oxford, UK
| | | | | | | | | |
Collapse
|
66
|
Sandri MI, Isaacs RJ, Ongkeko WM, Harris AL, Hickson ID, Broggini M, Vikhanskaya F. p53 regulates the minimal promoter of the human topoisomerase IIalpha gene. Nucleic Acids Res 1996; 24:4464-70. [PMID: 8948636 PMCID: PMC146283 DOI: 10.1093/nar/24.22.4464] [Citation(s) in RCA: 70] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
DNA topoisomerase IIalpha is an essential enzyme for chromosome segregation during mitosis. Consistent with a cell division-specific role, the expression of the topoisomerase IIalpha gene is strongly influenced by the proliferation status of cells. The p53 protein is one of the most important regulators of cell cycle progression in mammals, with an apparent dual role in the induction of cell cycle arrest following cytotoxic insults and in the regulation of the apoptotic cell death pathway. We have analysed whether p53 plays a role in regulating expression of the human topoisomerase IIalpha gene. We show that wild-type, but not mutant, p53 is able to decrease substantially the activity of the full length topoisomerase IIalpha gene promoter. Using a series of constructs comprising various deleted or mutated versions of the promoter lacking critical cis-acting elements, we show that this p53-specific regulation of the topoisomerase IIalpha promoter is independent of all characterised transcription factor binding sites and is directed at the minimal gene promoter. We conclude that expression of wild-type p53 induces downregulation of the human topoisomerase IIalpha promoter by acting on the basal transcription machinery. These findings implicate topoisomerase II as one of the downstream targets for p53-dependent regulation of cell cycle progression in human cells.
Collapse
Affiliation(s)
- M I Sandri
- Imperial Cancer Research Fund, University of Oxford, John Radcliffe Hospital, UK
| | | | | | | | | | | | | |
Collapse
|
67
|
Rattner JB, Hendzel MJ, Furbee CS, Muller MT, Bazett-Jones DP. Topoisomerase II alpha is associated with the mammalian centromere in a cell cycle- and species-specific manner and is required for proper centromere/kinetochore structure. J Biophys Biochem Cytol 1996; 134:1097-107. [PMID: 8794854 PMCID: PMC2120978 DOI: 10.1083/jcb.134.5.1097] [Citation(s) in RCA: 106] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
A study of the distribution of Topoisomerase II alpha (Topo II) in cells of six tissue culture cell lines, human (HeLa), mouse (L929), rat, Indian muntjac, rat kangaroo (PTK-2), and wallaby revealed the following features: (1) There is a cell cycle association of a specific population of Topo II with the centromere. (2) The centromere is distinguished from the remainder of the chromosome by the intensity of its Topo II reactivity. (3) The first appearance of a detectable population of Topo II at the centromere varies between species but is correlated with the onset of centromeric heterochromatin condensation. (4) Detectable centromeric Topo II declines at the completion of cell division. (5) The distribution pattern of Topo II within the centromere is species- and stage-specific and is conserved only within the kinetochore domain. In addition, we report that the Topo II inhibitor ICRF-193 can prevent the normal accumulation of Topo II at the centromere. This results in the disruption of chromatin condensation sub-adjacent to the kinetochore as well as the perturbation of kinetochore structure. Taken together, our studies indicate that the distribution of Topo II at the centromere is unlike that reported for the remainder of the chromosome and is essential for proper formation of centromere/kinetochore structure.
Collapse
Affiliation(s)
- J B Rattner
- Department of Anatomy, University of Calgary, Alberta Canada
| | | | | | | | | |
Collapse
|
68
|
Biersack H, Jensen S, Gromova I, Nielsen IS, Westergaard O, Andersen AH. Active heterodimers are formed from human DNA topoisomerase II alpha and II beta isoforms. Proc Natl Acad Sci U S A 1996; 93:8288-93. [PMID: 8710863 PMCID: PMC38663 DOI: 10.1073/pnas.93.16.8288] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
DNA topoisomerase II is a nuclear enzyme essential for chromosome dynamics and DNA metabolism. In mammalian cells, two genetically and biochemically distinct topoisomerase II forms exist, which are designated topoisomerase II alpha and topoisomerase II beta. In our studies of human topoisomerase II, we have found that a substantial fraction of the enzyme exists as alpha/beta heterodimers in HeLa cells. The ability to form heterodimers was verified when human topoisomerases II alpha and II beta were coexpressed in yeast and investigated in a dimerization assay. Analysis of purified heterodimers shows that these enzymes maintain topoisomerase II specific catalytic activities. The natural existence of an active heterodimeric subclass of topoisomerase II merits attention whenever topoisomerases II alpha and II beta function, localization, and cell cycle regulation are investigated.
Collapse
Affiliation(s)
- H Biersack
- Department of Molecular and Structural Biology, University of Aarhus, Denmark
| | | | | | | | | | | |
Collapse
|
69
|
Jensen S, Andersen AH, Kjeldsen E, Biersack H, Olsen EH, Andersen TB, Westergaard O, Jakobsen BK. Analysis of functional domain organization in DNA topoisomerase II from humans and Saccharomyces cerevisiae. Mol Cell Biol 1996; 16:3866-77. [PMID: 8668204 PMCID: PMC231383 DOI: 10.1128/mcb.16.7.3866] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The functional domain structure of human DNA topoisomerase IIalpha and Saccharomyces cerevisiae DNA topoisomerase II was studied by investigating the abilities of insertion and deletion mutant enzymes to support mitotic growth and catalyze transitions in DNA topology in vitro. Alignment of the human topoisomerase IIalpha and S. cerevisiae topoisomerase II sequences defined 13 conserved regions separated by less conserved or differently spaced sequences. The spatial tolerance of the spacer regions was addressed by insertion of linkers. The importance of the conserved regions was assessed through deletion of individual domains. We found that the exact spacing between most of the conserved domains is noncritical, as insertions in the spacer regions were tolerated with no influence on complementation ability. All conserved domains, however, are essential for sustained mitotic growth of S. cerevisiae and for enzymatic activity in vitro. A series of topoisomerase II carboxy-terminal truncations were investigated with respect to the ability to support viability, cellular localization, and enzymatic properties. The analysis showed that the divergent carboxy-terminal region of human topoisomerase IIalpha is dispensable for catalytic activity but contains elements that specifically locate the protein to the nucleus.
Collapse
Affiliation(s)
- S Jensen
- Department of Molecular Biology, University of Aarhus, Denmark
| | | | | | | | | | | | | | | |
Collapse
|
70
|
Abstract
In the course of anaphase, the chromosomal DNA is submitted to the traction of the spindle. Several physical problems are associated with this action. In particular, the sister chromatids are generally topologically intertwined at the onset of anaphase, and the removal of the intertwinings results from a coupling between the enzymatic action of type II DNA topoisomerases and the force exerted by the spindle. We propose a physical analysis of some of these problems: 1) We compare the maximum force the spindle can produce with the force required to break a DNA molecule, and define the conditions compatible with biological safety during anaphase. 2) We show that the behavior of the sister chromatids in the absence of type II DNA topoisomerases can be described by two distinct models: a chain pullout model accounts for the experimental observations made in the budding yeast, and a model of the mechanical rupture of rubbers accounts for the nondisjunction in standard cases. 3) Using the fluctuation-dissipation theorem, we introduce an effective protein friction associated with the strand-passing activity of type II DNA topoisomerases. We show that this friction can be used to describe the situation in which one chromosome passes entirely through another one. Possible experiments that could test these theoretical analyses are discussed.
Collapse
Affiliation(s)
- G Jannink
- Laboratoire Léon Brillouin (CEA-CNRS), Departement de Biologie Cellulaire et Moléculaire, CEA/Saclay, Gif-sur-Yvette, France
| | | | | |
Collapse
|
71
|
Smith MM, Yang P, Santisteban MS, Boone PW, Goldstein AT, Megee PC. A novel histone H4 mutant defective in nuclear division and mitotic chromosome transmission. Mol Cell Biol 1996; 16:1017-26. [PMID: 8622646 PMCID: PMC231084 DOI: 10.1128/mcb.16.3.1017] [Citation(s) in RCA: 68] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
The histone proteins are essential for the assembly and function of th e eukaryotic chromosome. Here we report the first isolation of a temperature-sensitive lethal histone H4 mutant defective in mitotic chromosome transmission Saccharomyces cerevisiae. The mutant requires two amino acid substitutions in histone H4: a lethal Thr-to-Ile change at position 82, which lies within one of the DNA-binding surfaces of the protein, and a substitution of Ala to Val at position 89 that is an intragenic suppressor. Genetic and biochemical evidence shows that the mutant histone H4 is temperature sensitive for function but not for synthesis, deposition, or stability. The chromatin structure of 2 micrometer circle minichromosomes is temperature sensitive in vivo, consistent with a defect in H4-DNA interactions. The mutant also has defects in transcription, displaying weak Spt- phenotypes. At the restrictive temperature, mutant cells arrest in the cell cycle at nuclear division, with a large bud, a single nucleus with 2C DNA content, and a short bipolar spindle. At semipermissive temperatures, the frequency of chromosome loss is elevated 60-fold in the mutant while DNA recombination frequencies are unaffected. High-copy CSE4, encoding an H3 variant related to the mammalian CENP-A kinetochore antigen, was found to suppress the temperature sensitivity of the mutant without suppressing the Spt- transcription defect. These genetic, biochemical, and phenotypic results indicate that this novel histone H4 mutant defines one or more chromatin-dependent steps in chromosome segregation.
Collapse
Affiliation(s)
- M M Smith
- Department of Microbiology, University of Virginia Cancer Center, Charlottesville, 22908, USA
| | | | | | | | | | | |
Collapse
|
72
|
Abstract
The distribution of topoisomerase II (Topo II) has been studied using immunofluorescence on cytocentrifuged preparations of mammalian chromosomes. Immunolabelling of Topo II is affected by choice of fixative, by barriers to accessibility and by the lability of the enzyme. Chromosomes still embedded in cytoplasm remain unlabelled, while in contrast Topo II can easily be lost from some sites in chromosomes free of cytoplasm. The definitive distribution of Topo II consists of a line along the centre of each chromatid, corresponding to the chromosome core or scaffold, and quantities of Topo II elsewhere in the chromosomes which vary during the course of mitosis. A strong reaction for Topo II can be seen throughout prophase chromosomes, consistent with a role in condensation and/or segregation of the chromosome arms at this stage. At metaphase, Topo II is restricted to the centromeric regions, the only parts of the chromosomes that still have to be separated at this stage, while in anaphase, after segregation has occurred, this centromeric concentration of Topo II is lost. The distribution and quantity of Topo II in mammalian chromosomes is thus wholly consistent with the known functions of this enzyme in chromosome condensation and segregation.
Collapse
Affiliation(s)
- A T Sumner
- MRC Human Genetics Unit, Western General Hospital, Edinburgh, UK
| |
Collapse
|
73
|
Duplantier B, Jannink G, Sikorav JL. Anaphase chromatid motion: involvement of type II DNA topoisomerases. Biophys J 1995; 69:1596-605. [PMID: 8534830 PMCID: PMC1236390 DOI: 10.1016/s0006-3495(95)80032-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
Sister chromatids are topologically intertwined at the onset of anaphase: their segregation during anaphase is known to require strand-passing activity by type II DNA topoisomerase. We propose that the removal of the intertwinings involves at the same time the traction of the mitotic spindle and the activity of topoisomerases. This implies that the velocity of the chromatids is compatible with the kinetic constraints imposed by the enzymatic reaction. We show that the greatest observed velocities (about 0.1 microns s-1) are close to the theoretical upper bound compatible with both the diffusion rate (calculated here within a probabilistic model) and the measured reaction rate of the enzyme.
Collapse
Affiliation(s)
- B Duplantier
- Service de Physique Théorique, CEA/Saclay, Gif-sur-Yvette, France
| | | | | |
Collapse
|
74
|
Giménez-Abián JF, Clarke DJ, Mullinger AM, Downes CS, Johnson RT. A postprophase topoisomerase II-dependent chromatid core separation step in the formation of metaphase chromosomes. J Cell Biol 1995; 131:7-17. [PMID: 7559788 PMCID: PMC2120606 DOI: 10.1083/jcb.131.1.7] [Citation(s) in RCA: 79] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Metaphase chromatids are believed to consist of loops of chromatin anchored to a central scaffold, of which a major component is the decatenatory enzyme DNA topoisomerase II. Silver impregnation selectively stains an axial element of metaphase and anaphase chromatids; but we find that in earlier stages of mitosis, silver staining reveals an initially single, folded midline structure, which separates at prometaphase to form two chromatid axes. Inhibition of topoisomerase II prevents this separation, and also prevents the contraction of chromatids that occurs when metaphase is arrested. Immunolocalization of topoisomerase II alpha reveals chromatid cores analogous to those seen with silver staining. We conclude that the chromatid cores in early mitosis form a single structure, constrained by DNA catenations, which must separate before metaphase chromatids can be resolved.
Collapse
|
75
|
Garrett-Engele P, Moilanen B, Cyert MS. Calcineurin, the Ca2+/calmodulin-dependent protein phosphatase, is essential in yeast mutants with cell integrity defects and in mutants that lack a functional vacuolar H(+)-ATPase. Mol Cell Biol 1995; 15:4103-14. [PMID: 7542741 PMCID: PMC230649 DOI: 10.1128/mcb.15.8.4103] [Citation(s) in RCA: 154] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
Calcineurin is a conserved Ca2+/calmodulin-dependent protein phosphatase that plays a critical role in Ca(2+)-mediated signaling in many cells. Yeast cells lacking functional calcineurin (cna1 cna2 or cnb1 mutants) display growth defects under specific environmental conditions, for example, in the presence of high concentrations of Na+, Li+, Mn2+, or OH- but are indistinguishable from wild-type cells under standard culture conditions. To characterize regulatory pathways that may overlap with calcineurin, we performed a synthetic lethal screen to identify mutants that require calcineurin on standard growth media. The characterization of one such mutant, cnd1-8, is presented. The CND1 gene was cloned, and sequence analysis predicts that it encodes a novel protein 1,876 amino acids in length with multiple membrane-spanning domains. CND1 is identical to the gene identified previously as FKS1, ETG1, and CWH53, cnd1 mutants are sensitive to FK506 and cyclosporin A and exhibit slow growth that is improved by the addition of osmotic stabilizing agents. This osmotic agent-remedial growth defect and microscopic evidence of spontaneous cell lysis in cnd1 cultures suggest that cell integrity is compromised in these mutants. Mutations in the genes for yeast protein kinase C (pkc1) and a MAP kinase (mpk1/slt2) disrupt a Ca(2+)-dependent signaling pathway required to maintain a normal cell wall and cell integrity. We show that pkc1 and mpk1/slt2 growth defects are more severe in the absence of calcineurin function and less severe in the presence of a constitutively active form of calcineurin. These observations suggest that calcineurin and protein kinase C perform independent but physiologically related functions in yeast cells. We show that several mutants that lack a functional vacuolar H(+)-ATPase (vma) require calcineurin for vegetative growth. We discuss possible roles for calcineurin in regulating intracellular ion homeostasis and in maintaining cell integrity.
Collapse
Affiliation(s)
- P Garrett-Engele
- Department of Biological Sciences, Stanford University, California 94305-5020
| | | | | |
Collapse
|
76
|
The yeast type I topoisomerase Top3 interacts with Sgs1, a DNA helicase homolog: a potential eukaryotic reverse gyrase. Mol Cell Biol 1994. [PMID: 7969174 DOI: 10.1128/mcb.14.12.8391] [Citation(s) in RCA: 389] [Impact Index Per Article: 13.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
We have previously shown that cells mutant for TOP3, a gene encoding a prokaryotic-like type I topoisomerase in Saccharomyces cerevisiae, display a pleiotropic phenotype including slow growth and genome instability. We identified a mutation, sgs1 (slow growth suppressor), that suppresses both the growth defect and the increased genomic instability of top3 mutants. Here we report the independent isolation of the SGS1 gene in a screen for proteins that interact with Top3. DNA sequence analysis reveals that the putative Sgs1 protein is highly homologous to the helicase encoded by the Escherichia coli recQ gene. These results imply that Sgs1 creates a deleterious topological substrate that Top3 preferentially resolves. The interaction of the Sgs1 helicase homolog and the Top3 topoisomerase is reminiscent of the recently described structure of reverse gyrase from Sulfolobus acidocaldarius, in which a type I DNA topoisomerase and a helicase-like domain are fused in a single polypeptide.
Collapse
|
77
|
Gangloff S, McDonald JP, Bendixen C, Arthur L, Rothstein R. The yeast type I topoisomerase Top3 interacts with Sgs1, a DNA helicase homolog: a potential eukaryotic reverse gyrase. Mol Cell Biol 1994; 14:8391-8. [PMID: 7969174 PMCID: PMC359378 DOI: 10.1128/mcb.14.12.8391-8398.1994] [Citation(s) in RCA: 290] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
We have previously shown that cells mutant for TOP3, a gene encoding a prokaryotic-like type I topoisomerase in Saccharomyces cerevisiae, display a pleiotropic phenotype including slow growth and genome instability. We identified a mutation, sgs1 (slow growth suppressor), that suppresses both the growth defect and the increased genomic instability of top3 mutants. Here we report the independent isolation of the SGS1 gene in a screen for proteins that interact with Top3. DNA sequence analysis reveals that the putative Sgs1 protein is highly homologous to the helicase encoded by the Escherichia coli recQ gene. These results imply that Sgs1 creates a deleterious topological substrate that Top3 preferentially resolves. The interaction of the Sgs1 helicase homolog and the Top3 topoisomerase is reminiscent of the recently described structure of reverse gyrase from Sulfolobus acidocaldarius, in which a type I DNA topoisomerase and a helicase-like domain are fused in a single polypeptide.
Collapse
Affiliation(s)
- S Gangloff
- Department of Genetics and Development, College of Physicians and Surgeons, Columbia University, New York, New York 10032
| | | | | | | | | |
Collapse
|
78
|
Affiliation(s)
- P M Watt
- Institute of Molecular Medicine, University of Oxford, John Radcliffe Hospital, U.K
| | | |
Collapse
|
79
|
DBF8, an essential gene required for efficient chromosome segregation in Saccharomyces cerevisiae. Mol Cell Biol 1994. [PMID: 8065366 DOI: 10.1128/mcb.14.9.6350] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
To investigate chromosome segregation in Saccharomyces cerevisiae, we examined a collection of temperature-sensitive mutants that arrest as large-budded cells at restrictive temperatures (L. H. Johnston and A. P. Thomas, Mol. Gen. Genet. 186:439-444, 1982). We characterized dbf8, a mutation that causes cells to arrest with a 2c DNA content and a short spindle. DBF8 maps to chromosome IX near the centromere, and it encodes a 36-kDa protein that is essential for viability at all temperatures. Mutational analysis reveals that three dbf8 alleles are nonsense mutations affecting the carboxy-terminal third of the encoded protein. Since all of these mutations confer temperature sensitivity, it appears that the carboxyl-terminal third of the protein is essential only at a restrictive temperature. In support of this conclusion, an insertion of URA3 at the same position also confers a temperature-sensitive phenotype. Although they show no evidence of DNA damage, dbf8 mutants exhibit increased rates of chromosome loss and nondisjunction even at a permissive temperature. Taken together, our data suggest that Dbf8p plays an essential role in chromosome segregation.
Collapse
|
80
|
Gerhold D, Thiyagarajan M, Kmiec EB. The topoisomerase I gene from Ustilago maydis: sequence, disruption and mutant phenotype. Nucleic Acids Res 1994; 22:3773-8. [PMID: 7937091 PMCID: PMC308361 DOI: 10.1093/nar/22.18.3773] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
The Ustilago maydis genomic TOP1 gene encoding DNA topoisomerase I was cloned by amplifying a gene fragment using the polymerase chain reaction, and using this fragment to search a genomic DNA library by hybridization. The predicted peptide sequence exhibited 30-40% identity to other eukaryotic TOP1 genes, yet differed in several features. First, an unusually long acidic region was identified near the amino terminus (28/29 residues are acidic), which resembles other nucleolar peptide motifs. Second, an atypical carboxy-terminal 'tail', absent in other TOP1 genes, followed the active site tyrosine residue. A top1 gene disruption mutant was constructed by replacing the genomic TOP1 gene, with a top1::HygR null allele. This mutant lost the abundant topoisomerase I activity evident in wild-type U.maydis, and displayed a subtle coloration phenotype evident during cell senescence.
Collapse
Affiliation(s)
- D Gerhold
- Department of Pharmacology, Jefferson Cancer Institute, Thomas Jefferson University, Philadelphia, PA 19107
| | | | | |
Collapse
|
81
|
Houman F, Holm C. DBF8, an essential gene required for efficient chromosome segregation in Saccharomyces cerevisiae. Mol Cell Biol 1994; 14:6350-60. [PMID: 8065366 PMCID: PMC359161 DOI: 10.1128/mcb.14.9.6350-6360.1994] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
To investigate chromosome segregation in Saccharomyces cerevisiae, we examined a collection of temperature-sensitive mutants that arrest as large-budded cells at restrictive temperatures (L. H. Johnston and A. P. Thomas, Mol. Gen. Genet. 186:439-444, 1982). We characterized dbf8, a mutation that causes cells to arrest with a 2c DNA content and a short spindle. DBF8 maps to chromosome IX near the centromere, and it encodes a 36-kDa protein that is essential for viability at all temperatures. Mutational analysis reveals that three dbf8 alleles are nonsense mutations affecting the carboxy-terminal third of the encoded protein. Since all of these mutations confer temperature sensitivity, it appears that the carboxyl-terminal third of the protein is essential only at a restrictive temperature. In support of this conclusion, an insertion of URA3 at the same position also confers a temperature-sensitive phenotype. Although they show no evidence of DNA damage, dbf8 mutants exhibit increased rates of chromosome loss and nondisjunction even at a permissive temperature. Taken together, our data suggest that Dbf8p plays an essential role in chromosome segregation.
Collapse
Affiliation(s)
- F Houman
- Department of Cellular and Developmental Biology, Harvard University, Cambridge, Massachusetts 02138
| | | |
Collapse
|
82
|
Bigioni M, Zunino F, Capranico G. Base mutation analysis of topoisomerase II-idarubicin-DNA ternary complex formation. Evidence for enzyme subunit cooperativity in DNA cleavage. Nucleic Acids Res 1994; 22:2274-81. [PMID: 8036155 PMCID: PMC523684 DOI: 10.1093/nar/22.12.2274] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023] Open
Abstract
Antitumor drugs, such as anthracyclines, interfere with mammalian DNA topoisomerase II by forming a ternary complex, DNA-drug-enzyme, in which DNA strands are cleaved and covalently linked to the enzyme. In this work, a synthetic 36-bp DNA oligomer derived from SV40 and mutated variants were used to determine the effects of base mutations on DNA cleavage levels produced by murine topoisomerase II with and without idarubicin. Although site competition could affect cleavage levels, mutation effects were rather similar among several cleavage sites. The major sequence determinants of topoisomerase II DNA cleavage without drugs are up to five base pairs apart from the strand cut, suggesting that DNA protein contacts involving these bases are particularly critical for DNA site recognition. Cleavage sites with adenines at positions -1 were detected without idarubicin only under conditions favouring enzyme binding to DNA, showing that these sites are low affinity sites for topoisomerase II DNA cleavage and/or binding. Moreover, the results indicated that the sequence 5'-(A)TA/(A)-3' (the slash indicates the cleaved bond, parenthesis indicate conditioned preference) from -3 to +1 positions constitutes the complete base sequence preferred by anthracyclines. An important finding was that mutations that improve the fit to the above consensus on one strand can also increase cleavage on the opposite strand, suggesting that a drug molecule may effectively interact with one enzyme subunit only and trap the whole dimeric enzyme. These findings documented that DNA recognition by topoisomerase II may occur at one or the other strand, and not necessarily at both of them, and that the two subunits can act cooperatively to cleave a double helix.
Collapse
Affiliation(s)
- M Bigioni
- Division of Experimental Oncology B, Istituto Nazionale per lo Studio e la Cura dei Tumori, Milan, Italy
| | | | | |
Collapse
|
83
|
Abstract
A set of carboxy-terminal deletion mutants of Saccharomyces cerevisiae DNA topoisomerase II were constructed for studying the functions of the carboxyl domain in vitro and in vivo. The wild-type yeast enzyme is a homodimer with 1,429 amino acid residues in each of the two polypeptides; truncation of the C terminus to Ile-1220 has little effect on the function of the enzyme in vitro or in vivo, whereas truncations extending beyond Gln-1138 yield completely inactive proteins. Several mutant enzymes with C termini in between these two residues were found to be catalytically active but unable to complement a top2-4 temperature-sensitive mutation. Immunomicroscopy results suggest that the removal of a nuclear localization signal in the C-terminal domain is likely to contribute to the physiological dysfunction of these proteins; the ability of these mutant proteins to relax supercoiled DNA in vivo shows, however, that at least some of the mutant proteins are present in the nuclei in a catalytically active form. In contrast to the ability of the catalytically active mutant proteins to relax supercoiled intracellular DNA, all mutants that do not complement the temperature-dependent lethality and high frequency of chromosomal nondisjunction of top2-4 were found to lack decatenation activity in vivo. The plausible roles of the DNA topoisomerase II C-terminal domain, in addition to providing a signal for nuclear localization, are discussed in the light of these results.
Collapse
|
84
|
Abstract
A set of carboxy-terminal deletion mutants of Saccharomyces cerevisiae DNA topoisomerase II were constructed for studying the functions of the carboxyl domain in vitro and in vivo. The wild-type yeast enzyme is a homodimer with 1,429 amino acid residues in each of the two polypeptides; truncation of the C terminus to Ile-1220 has little effect on the function of the enzyme in vitro or in vivo, whereas truncations extending beyond Gln-1138 yield completely inactive proteins. Several mutant enzymes with C termini in between these two residues were found to be catalytically active but unable to complement a top2-4 temperature-sensitive mutation. Immunomicroscopy results suggest that the removal of a nuclear localization signal in the C-terminal domain is likely to contribute to the physiological dysfunction of these proteins; the ability of these mutant proteins to relax supercoiled DNA in vivo shows, however, that at least some of the mutant proteins are present in the nuclei in a catalytically active form. In contrast to the ability of the catalytically active mutant proteins to relax supercoiled intracellular DNA, all mutants that do not complement the temperature-dependent lethality and high frequency of chromosomal nondisjunction of top2-4 were found to lack decatenation activity in vivo. The plausible roles of the DNA topoisomerase II C-terminal domain, in addition to providing a signal for nuclear localization, are discussed in the light of these results.
Collapse
Affiliation(s)
- P R Caron
- Department of Biochemistry and Molecular Biology, Harvard University, Cambridge, Massachusetts 02138
| | | | | |
Collapse
|
85
|
Guacci V, Hogan E, Koshland D. Chromosome condensation and sister chromatid pairing in budding yeast. J Biophys Biochem Cytol 1994; 125:517-30. [PMID: 8175878 PMCID: PMC2120001 DOI: 10.1083/jcb.125.3.517] [Citation(s) in RCA: 264] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
We have developed a fluorescent in situ hybridization (FISH) method to examine the structure of both natural chromosomes and small artificial chromosomes during the mitotic cycle of budding yeast. Our results suggest that the pairing of sister chromatids: (a) occurs near the centromere and at multiple places along the chromosome arm as has been observed in other eukaryotic cells; (b) is maintained in the absence of catenation between sister DNA molecules; and (c) is independent of large blocks of repetitive DNA commonly associated with heterochromatin. Condensation of a unique region of chromosome XVI and the highly repetitive ribosomal DNA (rDNA) cluster from chromosome XII were also examined in budding yeast. Interphase chromosomes were condensed 80-fold relative to B form DNA, similar to what has been observed in other eukaryotes, suggesting that the structure of interphase chromosomes may be conserved among eukaryotes. While additional condensation of budding yeast chromosomes were observed during mitosis, the level of condensation was less than that observed for human mitotic chromosomes. At most stages of the cell cycle, both unique and repetitive sequences were either condensed or decondensed. However, in cells arrested in late mitosis (M) by a cdc15 mutation, the unique DNA appeared decondensed while the repetitive rDNA region appeared condensed, suggesting that the condensation state of separate regions of the genome may be regulated differently. The ability to monitor the pairing and condensation of sister chromatids in budding yeast should facilitate the molecular analysis of these processes as well as provide two new landmarks for evaluating the function of important cell cycle regulators like p34 kinases and cyclins. Finally our FISH method provides a new tool to analyze centromeres, telomeres, and gene expression in budding yeast.
Collapse
Affiliation(s)
- V Guacci
- Department of Embryology, Carnegie Institution of Washington, Baltimore, Maryland 21210
| | | | | |
Collapse
|
86
|
Gangloff S, Lieber MR, Rothstein R. Transcription, topoisomerases and recombination. EXPERIENTIA 1994; 50:261-9. [PMID: 8143800 DOI: 10.1007/bf01924009] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/29/2023]
Abstract
Transcription, DNA topoisomerases and genetic recombination are interrelated for several structural reasons. Transcription can affect DNA topology, resulting in effects on recombination. It can also affect the chromatin structure in which the DNA resides. Topoisomerases can affect DNA and/or chromatin structure influencing the recombination potential at a given site. Here we briefly review the extent to which homologous direct repeat recombination and site-specific recombination in eukaryotes are affected by transcription and topoisomerases. In some cases, transcription or the absence of topoisomerases have little or no effect on recombination. In others, they are important components in the recombinational process. The common denominator of any effects of transcription and topoisomerases on recombination is their shared role in altering DNA topology.
Collapse
Affiliation(s)
- S Gangloff
- Department of Genetics & Development, College of Physicians & Surgeons, Columbia University, New York, New York 10032
| | | | | |
Collapse
|
87
|
Abstract
To elucidate yeast chromosome structure and behavior, we examined the breakage of entangled chromosomes in DNA topoisomerase II mutants by hybridization to chromosomal DNA resolved by pulsed-field gel electrophoresis. Our study reveals that large and small chromosomes differ in the nature and distribution of their intertwinings. Probes to large chromosomes (450 kb or larger) detect chromosome breakage, but probes to small chromosomes (380 kb or smaller) reveal no breakage products. Examination of chromosomes with one small arm and one large arm suggests that the two arms behave independently. The acrocentric chromosome XIV breaks only on the long arm, and its preferred region of breakage is approximately 200 kb from the centromere. When the centromere of chromosome XIV is relocated, the preferred region of breakage shifts accordingly. These results suggest that large chromosomes break because they have long arms and small chromosomes do not break because they have small arms. Indeed, a small metacentric chromosome can be made to break if it is rearranged to form a telocentric chromosome with one long arm or a ring with an "infinitely" long arm. These results suggest a model of chromosomal intertwining in which the length of the chromosome arm prevents intertwinings from passively resolving off the end of the arm during chromosome segregation.
Collapse
|
88
|
Abstract
To elucidate yeast chromosome structure and behavior, we examined the breakage of entangled chromosomes in DNA topoisomerase II mutants by hybridization to chromosomal DNA resolved by pulsed-field gel electrophoresis. Our study reveals that large and small chromosomes differ in the nature and distribution of their intertwinings. Probes to large chromosomes (450 kb or larger) detect chromosome breakage, but probes to small chromosomes (380 kb or smaller) reveal no breakage products. Examination of chromosomes with one small arm and one large arm suggests that the two arms behave independently. The acrocentric chromosome XIV breaks only on the long arm, and its preferred region of breakage is approximately 200 kb from the centromere. When the centromere of chromosome XIV is relocated, the preferred region of breakage shifts accordingly. These results suggest that large chromosomes break because they have long arms and small chromosomes do not break because they have small arms. Indeed, a small metacentric chromosome can be made to break if it is rearranged to form a telocentric chromosome with one long arm or a ring with an "infinitely" long arm. These results suggest a model of chromosomal intertwining in which the length of the chromosome arm prevents intertwinings from passively resolving off the end of the arm during chromosome segregation.
Collapse
Affiliation(s)
- R M Spell
- Department of Cellular and Developmental Biology, Harvard University, Cambridge, Massachusetts 02138
| | | |
Collapse
|
89
|
Esposito MS, Ramirez RM, Bruschi CV. Recombinators, recombinases and recombination genes of yeasts. Curr Genet 1994; 25:1-11. [PMID: 8082158 DOI: 10.1007/bf00712959] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Affiliation(s)
- M S Esposito
- Life Sciences Division, Lawrence Berkeley Laboratory, University of California, Berkeley 94720
| | | | | |
Collapse
|
90
|
Strunnikov AV, Larionov VL, Koshland D. SMC1: an essential yeast gene encoding a putative head-rod-tail protein is required for nuclear division and defines a new ubiquitous protein family. J Biophys Biochem Cytol 1993; 123:1635-48. [PMID: 8276886 PMCID: PMC2290909 DOI: 10.1083/jcb.123.6.1635] [Citation(s) in RCA: 240] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/29/2023] Open
Abstract
The smc1-1 mutant was identified initially as a mutant of Saccharomyces cerevisiae that had an elevated rate of minichromosome nondisjunction. We have cloned the wild-type SMC1 gene. The sequence of the SMC1 gene predicts that its product (Smc1p) is a 141-kD protein, and antibodies against Smc1 protein detect a protein with mobility of 165 kD. Analysis of the primary and putative secondary structure of Smc1p suggests that it contains two central coiled-coil regions flanked by an amino-terminal nucleoside triphosphate (NTP)-binding head and a conserved carboxy-terminal tail. These analyses also indicate that Smc1p is an evolutionary conserved protein and is a member of a new family of proteins ubiquitous among prokaryotes and eukaryotes. The SMC1 gene is essential for viability. Several phenotypic characteristics of the mutant alleles of smc1 gene indicate that its product is involved in some aspects of nuclear metabolism, most likely in chromosome segregation. The smc1-1 and smc1-2 mutants have a dramatic increase in mitotic loss of a chromosome fragment and chromosome III, respectively, but have no increase in mitotic recombination. Depletion of SMC1 function in the ts mutant, smc1-2, causes a dramatic mitosis-related lethality. Smc1p-depleted cells have a defect in nuclear division as evidenced by the absence of anaphase cells. This phenotype of the smc1-2 mutant is not RAD9 dependent. Based upon the facts that Smc1p is a member of a ubiquitous family, and it is essential for yeast nuclear division, we propose that Smc1p and Smc1p-like proteins function in a fundamental aspect of prokaryotic and eukaryotic cell division.
Collapse
Affiliation(s)
- A V Strunnikov
- Carnegie Institution of Washington, Department of Embryology, Baltimore, Maryland 21210
| | | | | |
Collapse
|
91
|
Abstract
Although the processes of mitosis and meiosis are similar, there is evidence for fundamental regulatory differences between the two. To examine these differences, we have compared the meiotic phenotype of DNA topoisomerase II mutants with their previously described mitotic phenotype (C. Holm, T. Goto, J. Wang, and D. Botstein, Cell 41:553-563, 1985). top2 mutants in meiosis show no defects in the latest detectable stages of recombination, yet they arrest prior to spindle establishment at meiosis I. Fluorescence and electron microscopy reveal that top2 mutants exhibit wild-type levels of meiotic chromosome condensation and form morphologically normal synaptonemal complex but are delayed in the exit from pachytene. Arrested cells retain viability and form colonies if transferred to mitotic medium. Our results suggest that the top2 meiotic arrest is regulatory in nature. This arrest may have evolved to ensure the resolution of fortuitous tangles between nonhomologous chromosomes.
Collapse
|
92
|
Abstract
Although the processes of mitosis and meiosis are similar, there is evidence for fundamental regulatory differences between the two. To examine these differences, we have compared the meiotic phenotype of DNA topoisomerase II mutants with their previously described mitotic phenotype (C. Holm, T. Goto, J. Wang, and D. Botstein, Cell 41:553-563, 1985). top2 mutants in meiosis show no defects in the latest detectable stages of recombination, yet they arrest prior to spindle establishment at meiosis I. Fluorescence and electron microscopy reveal that top2 mutants exhibit wild-type levels of meiotic chromosome condensation and form morphologically normal synaptonemal complex but are delayed in the exit from pachytene. Arrested cells retain viability and form colonies if transferred to mitotic medium. Our results suggest that the top2 meiotic arrest is regulatory in nature. This arrest may have evolved to ensure the resolution of fortuitous tangles between nonhomologous chromosomes.
Collapse
Affiliation(s)
- D Rose
- Department of Cellular and Developmental Biology, Harvard University, Cambridge, Massachusetts 02138
| | | |
Collapse
|
93
|
Gudkov AV, Zelnick CR, Kazarov AR, Thimmapaya R, Suttle DP, Beck WT, Roninson IB. Isolation of genetic suppressor elements, inducing resistance to topoisomerase II-interactive cytotoxic drugs, from human topoisomerase II cDNA. Proc Natl Acad Sci U S A 1993; 90:3231-5. [PMID: 8386368 PMCID: PMC46273 DOI: 10.1073/pnas.90.8.3231] [Citation(s) in RCA: 106] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Many cytotoxic anticancer drugs act at topoisomerase II (topo II) by stabilizing cleavable complexes with DNA formed by this enzyme. Several cell lines, selected for resistance to topo II-interactive drugs, show decreased expression or activity of topo II, suggesting that such a decrease may be responsible for drug resistance. In the present study, etoposide resistance was used as the selection strategy to isolate genetic suppressor elements (GSEs) from a retroviral library expressing random fragments of human topo II (alpha form) cDNA. Twelve GSEs were isolated, encoding either peptides corresponding to short segments of the topo II alpha molecule (2.4-6.5% of the protein) or 163- to 220-bp-long antisense RNA sequences. Expression of a GSE encoding antisense RNA led to decreased cellular expression of the topo II alpha protein. Both types of GSE induced resistance to several topo II poisons but not to drugs that do not act at topo II. These results provide direct evidence that inhibition of topo II results in resistance to topo II-interactive drugs, indicate structural domains of topo II capable of independent functional interactions, and demonstrate that expression selection of random fragments constitutes an efficient approach to the generation of GSEs in mammalian cells.
Collapse
MESH Headings
- Antineoplastic Agents/pharmacology
- Base Sequence
- Cloning, Molecular
- DNA Topoisomerases, Type II/genetics
- DNA, Neoplasm/genetics
- DNA, Neoplasm/isolation & purification
- Drug Resistance/genetics
- Etoposide/pharmacology
- Gene Library
- Genes, Suppressor
- HeLa Cells
- Humans
- Leukemia, Myelogenous, Chronic, BCR-ABL Positive
- Molecular Sequence Data
- Oligodeoxyribonucleotides
- Plasmids
- Polymerase Chain Reaction/methods
- RNA, Antisense/genetics
- Retroviridae/genetics
- Topoisomerase II Inhibitors
- Tumor Cells, Cultured
Collapse
Affiliation(s)
- A V Gudkov
- Department of Genetics, University of Illinois, Chicago 60612-7309
| | | | | | | | | | | | | |
Collapse
|
94
|
Runge KW, Zakian VA. Saccharomyces cerevisiae linear chromosome stability (lcs) mutants increase the loss rate of artificial and natural linear chromosomes. Chromosoma 1993; 102:207-17. [PMID: 8458255 DOI: 10.1007/bf00387735] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023]
Abstract
We isolated mutants of Saccharomyces cerevisiae that lose a 100 kb linear yeast artificial chromosome (YAC) at elevated rates. Mutations in two of these LCS (linear chromosome stability) genes had little or no effect on the loss rate of a circular YAC that had the same centromere and origin of replication as present on the linear YAC. Moreover, mutations in these LCS genes also increased the loss rate of an authentic linear yeast chromosome, chromosome III, but had only small effects on the loss rate of a circular derivative of chromosome III. As these mutants preferentially destabilize linear chromosomes, they may affect chromosome stability through interactions at telomeres. Telomeres are thought to be essential for the protection and complete replication of chromosome ends. The cytological properties of telomeres suggest that these structures may play additional roles in chromosome function. The lengths of the terminal C1-3A repeats at the ends of yeast chromosomes were unaltered in the linear preferential lcs mutants, suggesting that these mutants do not affect the replication or protection of telomeric DNA. Thus, the linear-preferential lcs mutants may identify a role for telomeres in chromosome stability that is distinct from their function in the replication and protection of chromosomal termini.
Collapse
Affiliation(s)
- K W Runge
- Fred Hutchinson Cancer Research Center, Seattle, WA 98104
| | | |
Collapse
|
95
|
Abstract
Although rare, a recessive temperature-sensitive calmodulin mutant has been isolated in Saccharomyces cerevisiae. The mutant carries two mutations in CMD1, isoleucine 100 is changed to asparagine and glutamic acid 104 is changed to valine. Neither mutation alone conferred temperature sensitivity. A single mutation that allowed production of an intact but defective protein was not identified. At the nonpermissive temperature, the temperature-sensitive mutant displayed multiple defects. Bud formation and growth was delayed, but this defect was not responsible for the temperature-sensitive lethality. Cells synchronized in G1 progressed through the cell cycle and retained viability until the movement of the nucleus to the neck between the mother cell and the large bud. After nuclear movement, less than 5% of the cells survived the first mitosis and could form colonies when returned to permissive conditions. The duplicated DNA was dispersed along the spindle, extending from mother to daughter cell. Cells synchronized in G2/M lost viability immediately upon the shift to the nonpermissive temperature. At a semipermissive temperature, the mutant showed approximately a 10-fold increase in the rate of chromosome loss compared to a wild-type strain. The mitotic phenotype is very similar to yeast mutants that are defective in chromosome disjunction. The mutant also showed defects in cytokinesis.
Collapse
Affiliation(s)
- T N Davis
- Department of Biochemistry, University of Washington, Seattle
| |
Collapse
|
96
|
Shamu CE, Murray AW. Sister chromatid separation in frog egg extracts requires DNA topoisomerase II activity during anaphase. J Cell Biol 1992; 117:921-34. [PMID: 1315785 PMCID: PMC2289485 DOI: 10.1083/jcb.117.5.921] [Citation(s) in RCA: 181] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
We have produced metaphase spindles and induced them to enter anaphase in vitro. Sperm nuclei were added to frog egg extracts, allowed to replicate their DNA, and driven into metaphase by the addition of cytoplasm containing active maturation promoting factor (MPF) and cytostatic factor (CSF), an activity that stabilizes MPF. Addition of calcium induces the inactivation of MPF, sister chromatid separation and anaphase chromosome movement. DNA topoisomerase II inhibitors prevent chromosome segregation at anaphase, demonstrating that the chromatids are catenated at metaphase and that decatenation occurs at the start of anaphase. Topoisomerase II activity towards exogenous substrates does not increase at the metaphase to anaphase transition, showing that chromosome separation at anaphase is not triggered by a bulk activation of topoisomerase II.
Collapse
Affiliation(s)
- C E Shamu
- Department of Biochemistry and Biophysics, University of California, San Francisco 94143
| | | |
Collapse
|
97
|
Abstract
We purified fission yeast DNA topoisomerase II (topo II) to apparent homogeneity. It consists of a single 165-kDa polypeptide in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and, upon treatment with a bifunctional reagent, doubles its molecular weight. Limited proteolysis of intact topo II by papain produces a 125-kDa core, which lacks the N-terminal 75 and the C-terminal approximately 260 amino acids but still contains regions similar to those of bacterial or phage T4 topo II subunits. The core retains relaxing and unknotting activities. Further digestion inactivates the core, cleaving it at the middle of the GyrB-like domain and at the beginning of the GyrA-like domain. Therefore, papain appears to cleave spatially distinct subdomains of topo II. We made top2 mutant genes deleted of the C-terminal 286 or N-terminal 74 amino acids, which can substitute for the wild-type top2+ gene in mitosis and meiosis. However, a mutant containing deletions of both termini cannot rescue the top2 null mutant, despite the fact that the product is enzymatically active. Therefore, the top2 product of the doubly truncated gene may not fulfill all of the in vivo requirements for top2+ function.
Collapse
|
98
|
Shiozaki K, Yanagida M. A functional 125-kDa core polypeptide of fission yeast DNA topoisomerase II. Mol Cell Biol 1991; 11:6093-102. [PMID: 1658625 PMCID: PMC361784 DOI: 10.1128/mcb.11.12.6093-6102.1991] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
We purified fission yeast DNA topoisomerase II (topo II) to apparent homogeneity. It consists of a single 165-kDa polypeptide in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and, upon treatment with a bifunctional reagent, doubles its molecular weight. Limited proteolysis of intact topo II by papain produces a 125-kDa core, which lacks the N-terminal 75 and the C-terminal approximately 260 amino acids but still contains regions similar to those of bacterial or phage T4 topo II subunits. The core retains relaxing and unknotting activities. Further digestion inactivates the core, cleaving it at the middle of the GyrB-like domain and at the beginning of the GyrA-like domain. Therefore, papain appears to cleave spatially distinct subdomains of topo II. We made top2 mutant genes deleted of the C-terminal 286 or N-terminal 74 amino acids, which can substitute for the wild-type top2+ gene in mitosis and meiosis. However, a mutant containing deletions of both termini cannot rescue the top2 null mutant, despite the fact that the product is enzymatically active. Therefore, the top2 product of the doubly truncated gene may not fulfill all of the in vivo requirements for top2+ function.
Collapse
Affiliation(s)
- K Shiozaki
- Department of Biophysics, Faculty of Science, Kyoto University, Japan
| | | |
Collapse
|
99
|
Downes CS, Mullinger AM, Johnson RT. Inhibitors of DNA topoisomerase II prevent chromatid separation in mammalian cells but do not prevent exit from mitosis. Proc Natl Acad Sci U S A 1991; 88:8895-9. [PMID: 1656458 PMCID: PMC52617 DOI: 10.1073/pnas.88.20.8895] [Citation(s) in RCA: 125] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
DNA topoisomerase II (EC 5.99.1.3) is necessary for chromosome condensation and disjunction in yeast but not for other functions. In mammalian cells, it has been reported to be necessary for progression toward mitosis but not for transit through mitosis. We have found, on the contrary, that specific inhibition of topoisomerase II (but not of topoisomerase I) interferes with mammalian mitotic progression. Metaphase is prolonged, and anaphase separation of chromatids is completely inhibited, in cells given high concentrations of topoisomerase II inhibitors; nevertheless these cells attempt cleavage, sometimes generating nucleate and anucleate daughters. Lower concentrations of inhibitors interfere with anaphase and produce abnormalities of segregation. DNA topoisomerase II activity is therefore necessary for mammalian chromatid separation, but it is not tightly coupled to the control of other mitotic events.
Collapse
Affiliation(s)
- C S Downes
- Department of Zoology, University of Cambridge, United Kingdom
| | | | | |
Collapse
|
100
|
Abstract
Changes in the morphology of human and murine chromosomes during the different stages of mitosis have been examined by scanning electron microscopy. Two important findings have emerged from this study. The first is that prophase chromosomes do not become split into pairs of chromatids until late prophase or early metaphase. This entails two distinct processes of condensation, the earlier one starting as condensations of chromosomes into chromomeres which then fuse to form a cylindrical body. After this cylindrical body has split in two longitudinally, further condensation occurs by mechanisms that probably include coiling of the chromatids as well as other processes. The second finding is that the centromeric heterochromatin does not split in two at the same time as the rest of the chromosome, but remains undivided until anaphase. It is proposed that the function of centromeric heterochromatin is to hold the chromatids together until anaphase, when they are separated by the concerted action of topoisomerase II acting on numerous similar sites provided by the repetitive nature of the satellite DNA in the heterochromatin. A lower limit to the size of blocks of centromeric heterochromatin is placed by the need for adequate mechanical strength to hold the chromatids together, and a higher limit by the necessity for rapid splitting of the heterochromatin at anaphase. Beyond these limits malsegregation will occur, leading to aneuploidy. Because the centromere remains undivided until anaphase, it cannot undergo the later stage of condensation found in the chromosome arms after separation into chromatids, and therefore the centromere remains as a constriction.
Collapse
Affiliation(s)
- A T Sumner
- MRC Human Genetics Unit, Western General Hospital, Edinburgh, UK
| |
Collapse
|