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  • 1
    ISSN: 1432-0983
    Keywords: Physarum is mutants Cell cycle Synchronization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary A screening procedure for cell cycle mutants among is mutants of Physarum has been developed for unsynchronized microplasmodia. The synchronization of the microplasmodia and the ratio of pre- to post-mitotic nuclei were evaluated after a transient shift-up to the non-permissive temperature. In contrast with wild type and is mutants not blocked in a cell cycle event, putative cell cycle mutants were synchronized. Among them, three strains which showed a reduction of DNA synthesis had an abnormally increased ratio of pre- to post-mitotic nuclei. Thus, this methodology seems to be efficient and more rapid than the previously published procedures for detecting cell-cycle mutants of Physarum.
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  • 2
    ISSN: 1432-0843
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The action of two epimers of a new vinblastine derivative that differ in their in vivo antitumor activity and their cytotoxicity was studied in vitro in brain microtubule proteins. These two compounds, called S-12363 and S-12362, could not be distinguished from one another or from other active vinca alkaloids by their ability to prevent microtubule assembly. However, they differed strongly both from one another and from vincristine and vinblastine in their ability to induce the formation of tubulin paracrystals and in the stability of the paracrystals following temperature shifts from 0° to 37°C and vice versa. The most potent drugs, S-12363, induced considerable tubulin aggregation, which was even more pronounced than that observed in the presence of vincristine. Previous results have shown that S-12363, in contrast to vincristine, induces no neurotoxic effects. This observation is in disagreement with a direct relationship between tubulin aggregation and neurotoxicity.
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  • 3
    ISSN: 1617-4623
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary Physarum synchronous plasmodia were submitted to temperature shifts during the cell cycle and the onset of mitosis was followed at both temperatures. After 22 to 31 or 32° shifts, delays in mitosis onset, dependent upon protein synthesis, were observed at 32° and found to increase as the time separating the shift from the control mitosis decreases. The modification of a general metabolic process or the inactivation of a catalytic heat sensitive substance cannot account for such a result. The proposed model postulates a substance acting in a stoichiometric way, which can occur under three structural forms: two active forms synthesized at low and high temperatures respectively and an inactive one which comes from the transformation of the low temperature active form placed at high temperature. The constant delays observed after some shifts (29 to 32°) suggest that this substance is acting through a polymeric structure which would be necessary for the mitotic process and the initiation of the following DNA synthesis.
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  • 4
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1399-3054
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The cytoskeleton is involved in major developmental events in plant cell growth and differentiation. Nucleation events play a key role in the dynamic and organization of the microtubule (Mt) cytoskeleton. Among many proteins involved in Mt nucleation, γ-tubulin has been identified as an essential component of the Mt organizing centers (MTOC). In protoplasts, somatic embryogenesis induction has been correlated with remodeling of Mt cytoskeleton. We have investigated the specific developmental expression of γ-tubulin in Helianthus annuus. Two γ-tubulin isoforms have been detected by immunoblotting, with bands at 52 and 58 kDa. The larger γ-tubulin (58 kDa) is present in all the sunflower tissues tested and is associated with the nucleus. The smaller γ-tubulin (52 kDa), differing from the former at the carboxy-terminal end, is only present in meristematic and dedifferentiated cells and is not bound to the nucleus. This first demonstration of the presence of two γ-tubulins in plant cells is discussed in terms of distinct roles in the nucleation and organization of Mts.
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  • 6
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
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  • 7
    ISSN: 0886-1544
    Keywords: maytansine ; vinblastine ; diphenylpyridazone ; colchicine ; taxol ; tubulin ; microtubule ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: We have investigated the effects of the microtubule poison rhazinilam on microtubule assembly in vivo and in vitro. In mammalian cells, rhazinilam mimics the effects of taxol and leads to microtubule bundles, multiple asters, and microtubule cold stability. In vitro, rhazinilam protected preassembled microtubules from cold-induced disassembly, but not from calcium ion-induced disassembly. Moreover, both at 0°C and at 37°C, rhazinilam induced the formation of anomalous tubulin assemblies (spirals). This process was prevented by maytansine and vinblastine, but not by colchicine. Preferential saturable and stoichiometric binding of radioactive rhazinilam to tubulin in spirals was observed with a dissociation constant of 5 μM. This binding was abolished in the presence of vinblastine and maytansine. In contrast, specific binding of radioactive rhazinilam to tubulin assembled in microtubules was undetectable. These results demonstrate that rhazinilam alters microtubule stability differently than taxol, and that the overall similar effects of rhazinilam and taxol on the cellular cytoskeleton are the consequence of two distinct mechanisms of action at the molecular level. © 1994 Wiley-Liss, Inc.
    Additional Material: 6 Ill.
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  • 8
    ISSN: 0886-1544
    Keywords: peptide antibodies ; protein processing ; axonemes ; microtubule associated proteins ; UV photocleavage ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Dyneins are multi-subunit enzymes that transduce chemical energy into the mechanical energy that makes cilia and flagella beat and moves organelles towards the minus end of microtubules. The ATPase activity is borne by heavy chains, and recent molecular analysis indicates that dynein heavy chain genes form an ancient multigene family: the similarity between the same isoform of two distantly related species is greater than that between different isoforms of the same species. We have exploited sequence identities between a Paramecium axonemal dynein heavy chain gene cloned in our laboratory and sequences of dynein heavy chains from other species to prepare antibodies against active-site peptides capable of recognizing dynein heavy chains regardless of species or isoform. One of the antibodies is perfectly specific for the larger product of V1 photolysis (HUV1) and thus incorporates a unique property of the hydrolytic ATP binding site of all known dynein heavy chains, the capacity for photocleavage in the presence of micromolar vanadate. Our characterization of these reagents suggests that they will be useful for biochemical and in situ studies of known dyneins as well as identification of potential new members of the family. © 1994 Wiley-Liss, Inc.
    Additional Material: 3 Ill.
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  • 9
    ISSN: 0886-1544
    Keywords: microtubule-associated proteins ; cell cycle ; phosphorylation ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Microtubule-interacting proteins have been studied in the lower eukaryote Physarum polycephalum. We show for the first time 1) the presence in Physarum amoebal crude extracts of at least six polypeptides that bind specifically to amoebal microtubules, 2) the binding between these proteins and mammalian microtubules, 3) the heat stability of two of these polypeptides (125 and 235 kDa), 4) the functional properties of a fraction containing a heat-soluble 125 kDa polypeptide, and 5) the phosphorylation of the 125 kDa polypeptide during two distinct periods of the cell cycle in Physarum synchronous plasmodia, first at late S/early G2 phase and second at late G2/prophase.
    Additional Material: 8 Ill.
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  • 10
    ISSN: 0886-1544
    Keywords: tubulin structure ; microtubule ; antibody ; microtubule poison ; Life and Medical Sciences ; Cell & Developmental Biology
    Source: Wiley InterScience Backfile Collection 1832-2000
    Topics: Biology , Medicine
    Notes: Polyclonal antibodies have been raised against the peptide 28-38 of the β-subunit of the tubulin heterodimer in order to study the accessibility of this region in the tubulin heterodimer and in various tubulin assemblies. These antibodies were specific for all β'-tubulin subunits, except for β-tubulin isotypes, and did not recognize the α-tubulin subunit. The 28-38 region does not play a role in the interaction between the α-and β-subunits since it was accessible to the antibodies on the native heterodimer. The accessibility of the antibodies was not modified by several microtubular poisons. In contrast, in all tubulin assemblies obtained in the presence of microtubule associated proteins, the region 28-38 was not available to the antibodies. These antibodies did not react with microtubules or tubulin spirals assembled either from microtubule proteins or from pure tubulin when these tubulin assemblies were probed in the absence of free tubulin after centrifugation on glass coverslips. In addition, antibodies failed to interact with the microtubule cytoskeleton in cultured Ptk2 cells indicating that the 28-38 region of β-tubulin is also protected in cellular structures. These observations suggest that the 28-38 region of the β-tubulin subunit is either located in a zone of interaction between two successive tubulin dimers within a protofilament or hidden by an allosteric conformational change which occurs during tubulin assembly. © 1992 Wiley-Liss, Inc.
    Additional Material: 7 Ill.
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