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84931558427
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Tubulin is actually the generic name of several nearly identical globular proteins individually referred to with the prefix alpha, beta, or gamma. Most tubulin in nature exists as a heterodimer of one alpha-tubulin and one beta-tubulin molecule (molecular weight app 110 000 daltons). For the purposes of this paper, the name tubulin refers to this heterodimer. The dimer is approximately 40-Å wide and 80-Å long.
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0014382446
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alpha and beta tubulin each associate with a molecule of GTP: alpha tubulin binds GTP nonexchangeably while beta tubulin binds GTP exchangeably with an affinity that depends on the concentration of Mg2+.
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(1968)
Biochemistry
, vol.7
, pp. 4466
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Weisenberg, R.C.1
Borisy, G.G.2
Taylor, E.W.3
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4
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84931558430
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The attraction between tubulin dimers comes from weak intermolecular interactions such as hydrophobic and van der Waals interactions.
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5
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0022483059
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The microtubule has a crystalline organization. Tubulin dimers align head to tail in parallel protofilaments, lining the wall of the microtubule. There are typically 13 protofilaments. Neighboring protofilaments are offset by app 9 Å, creating a pattern of three intertwined helices. The microtubule is a polar structure: one end (known as the minus end) exposes only alpha tubulin and the other (the plus end) exposes only beta.
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(1986)
J. Cell. Biol.
, vol.102
, pp. 1067
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Mandelkow, E.M.1
Schultheiss, R.2
Rapp, R.3
Müller, M.4
Mandelkow, E.5
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19
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Certain proteins, known as microtubule-associated proteins (MAP's), bind to microtubules in the cell and modify dynamic instability.
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We use axoneme fragments to nucleate microtubules. Axonemes are the backbone structure of flagella [5]. They are a bundle of 11 microtubules, 9 so-called doublet microtubules in a circle around two single microtubules, stabilized and held together by other proteins. Thus each axoneme fragment contains 22 nucleating sites, 11 plus ends on one side, and 11 minus ends on the other [4]. Our particular axonemes come from the sperm of sea urchins from the laboratory of Professor E. D. Salmon. A protocol for isolating axoneme fragments is given in Ref. [10(c)].
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It should be noted that there is no significant effect of the glass surface on microtubule growth, because growth is a slow process as compared to diffusion. Solving the diffusion equation for typical tubulin concentrations and microtubule growth rates leads to a characteristic depletion length lD= ω /4 π DC app 10 Å, where omega is the number of monomers sticking to the microtubule end per unit time (1625/min), D is the diffusion constant for tubulin dimers (4 times 10-7 cm2/sec), and C is the concentration of tubulin dimers ( app 10 μ M).
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We use a type E thermocouple with 13-mum wires and a platinum RTD from Omega Engineering.
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B. D. Hames in Gel Electrophoresis of Proteins: A Practical Approach, 2nd ed., edited by B. D. Hames and D. Rickwood (Oxford University Press, Oxford, 1990).
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The nucleation sites are arranged such that 11 sites are close together [14]. While competition between sites is not a factor [15] when more than four microtubules are growing on the same axoneme end, shorter microtubules are not visible among the stalks of the longer ones.
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84931558439
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We determined that the distributions were static by splitting the lengths into two one-hour intervals and comparing the histograms.
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84931558441
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R. C. Williams in The Cytoskeleton: A Practical Approach, edited by K. L. Carraway and C. A. C. Carraway (Oxford University Press, New York, 1992).
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