Centrosomes Isolated from Spisula solidissima Oocytes Contain Rings and an Unusual Stoichiometric Ratio of α/β Tubulin |
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| Authors: | Jacalyn M Vogel Tim Stearns Conly L Rieder and Robert E Palazzo |
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| Institution: | *The Department of Physiology and Cell Biology, University of Kansas, Lawrence, Kansas 66045, and the Marine Biological Laboratory, Woods Hole, Massachusetts 02543; ?Department of Biological Sciences, Stanford University, Palo Alto, California 94305; and §Wadsworth Center for Laboratories and Research, Albany, New York 12201-0509 |
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| Abstract: | Centrosome-dependent microtubule nucleation involves the interaction of tubulin subunits with pericentriolar material. To study the biochemical and structural basis of centrosome-dependent microtubule nucleation, centrosomes capable of organizing microtubules into astral arrays were isolated from parthenogenetically activated Spisula solidissima oocytes. Intermediate voltage electron microscopy tomography revealed that each centrosome was composed of a single centriole surrounded by pericentriolar material that was studded with ring-shaped structures ~25 nm in diameter and <25 nm in length. A number of proteins copurified with centrosomes including: (a) proteins that contained M-phase–specific phosphoepitopes (MPM-2), (b) α-, β-, and γ-tubulins, (c) actin, and (d) three low molecular weight proteins of <20 kD. γ-Tubulin was not an MPM-2 phosphoprotein and was the most abundant form of tubulin in centrosomes. Relatively little α- or β-tubulin copurified with centrosomes, and the ratio of α- to β-tubulin in centrosomes was not 1:1 as expected, but rather 1:4.6, suggesting that centrosomes contain β-tubulin that is not dimerized with α-tubulin. |
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